FOAM STABILITY.

Abstract

The present invention relates to a beer containing reduced amounts of AcHFA. Beer with reduced amounts of AcHFA has been found to have improved foam stability. The invention provides beer with reduced amounts of AcHFA, as well as methods for removing AcHFA from beer during or after fermentation, or for removing an AcHFA precursor from wort.

Description

FOAM STABILITY The invention relates to a beer with improved foam stability, as well as methods for improving beer foam stability. Background. Beer is one of the most popular alcoholic beverages worldwide. It is prepared by fermenting an aqueous matrix containing sugar derived from grains, using yeast, which converts the sugars into ethanol (alcohol). The beer production process is generally known, and a knowledgeable person is able to brew beer based on common knowledge (see, for example, The Brewers Handbook (second edition), by Ted Goldammer (2008, Apex Publications) and the information disclosed here). Beer is commonly made from grains such as barley, although other types of grains, including wheat and sorghum, can also be used. Beer is typically produced through a process that includes the following basic steps: mashing a mixture of grains and water to produce a mash; separating the mash into wort and spent grain; boiling the wort to produce boiled wort; fermenting the boiled wort with live yeasts (such as Saccharomyces pastorianus or Saccharomyces cerevisiae) to produce fermented wort; subjecting the fermented wort to one or more additional process steps (e.g., maturation and filtration) to produce beer; and packaging the beer in a sealed container, such as a bottle, can, or keg. In an exemplary process for producing a barley malt beer, the barley is malted, meaning it is germinated and then dried (baked) to produce malt. This process is important for the formation of flavor and color compounds, as well as enzymes that are crucial for further flavor development and starch breakdown. The malt is then milled and steeped in water (mashing). The mash is heated to facilitate starch breakdown. Subsequent filtration produces wort, which is a more or less clarified aqueous solution of fermentable sugars, also containing various flavors and aromas, and many other compounds. Both desirable and undesirable flavor compounds are present in the wort. The wort is boiled to sterilize it, precipitate proteins, and concentrate it. Hops are optionally added for bitterness and flavor. After the precipitate is removed, this mixture undergoes fermentation. Fermentation converts fermentable sugars into ethanol and carbon dioxide, and also produces various new flavor compounds. Simultaneously, the yeast used in fermentation carries out many other chemical conversions. After fermentation, the beer can be filtered and / or stored to optimize its appearance and flavor. frCALnn / Lznz / E / Yi An important aspect of beer is the head. The head is a layer of foam on top of the beer. This foam comes from carbon dioxide present in the beer due to fermentation and / or post-fermentation additions, but which essentially dissolves in the beer as a result of the high pressure in the beer container (e.g., a can or a bottle). Releasing the beer from the container, for example, into a glass, causes carbon dioxide bubbles to form, which rise through the liquid to the top of the glass, creating foam. A distinctive characteristic of beer foam is its stability. Unlike other yeast-fermented sparkling beverages (e.g., champagne), beer foam is stable. This is due, among other things, to proteins and hop acids isomerized in the beer, which, during the formation and rise of the carbon dioxide bubbles through the beer, are positioned at the interface between the bubbles and the liquid. Upon reaching the top of the liquid, these components stabilize the beer foam bubbles. As a result, the foam layer remains intact for an extended period. An intact and stable foam layer is considered an important aspect of a pleasant beer. However, the foam stabilization is short-lived. Within minutes of pouring, the foam layer thins, and eventually, no foam remains. This process can happen faster than the time it takes for the consumer to finish the beer. This means the beer is enjoyed less over time due to the disappearing foam layer. For slow drinkers, the foam may have disappeared even before they finish the beer. The present invention provides beers that have improved foam stability and methods for improving beer foam stability. Summary of the invention. The present invention relates to a beer containing reduced amounts of AcHFA. Beer with reduced amounts of AcHFA has been found to have improved foam stability. The invention provides beer with reduced amounts of AcHFA, as well as methods for removing AcHFA from beer during or after fermentation, or for removing an AcHFA precursor from wort. Brief description of the Figures. Figure 1: Comparison of foam stability before and after an adsorption process with methylcellulose ester adsorbent. Figures 2a-2b: The effect of AcHFA addition on beer foam stability with hops (2a) and without hops (2b). frCRLnn / Lznz / E / Yii Figures 3a-3b: The effect of AcHFA removal from hoppy (3a) and non-hoppy (3b) beer. Figure 4: Removal of AcHFA from beer by a variety of adsorbents. Figure 5: The activity of two adsorbents in the removal of AcHFA from beer. Figure 6: Installation of an adsorbent filter in an industrial-scale brewing process. Figure 7a: ATF-1 mutations in yeast. Figure 7b: Ethanol production of ATF-1 deficient yeast (strain a), ATF-2 deficient yeast (strain b), and yeast deficient in both ATF-1 and ATF-2 (strain c), compared to unmodified yeast (WT). Figures 8a and 8b: Exemplary configurations for removing AcHFA from beer on a relevant factory scale. Figure 9: Greater foam stability in beer produced using a relevant factory scale. Detailed description of the invention. The invention provides a beer comprising less than 2 mg / L of AcHFA, where AcHFA is a C12-C22 fatty acid comprising a carboxylic acid group and a linear CI 1-C21 alkyl group, where said alkyl group may be partially unsaturated, and where said alkyl group is substituted with at least one hydroxy group and at least one acetate group. Preferably, the beer comprises less than 1.5 mg / L of AcHFA, preferably less than 1.0 mg / L, more preferably less than 0.5 mg / L, even more preferably less than 0.25 mg / L, and even more preferably less than 0.1 mg / L. Therefore, the invention relates to beer comprising certainly less than 10 mg / l, such as less than 9 mg / l, less than 8 mg / l, less than 7 mg / l, less than 6 mg / l, less than 5 mg / l, less than 4 mg / l of AcHFA, or less than 3 mg / l. AcHFA has now been found to form during the regular fermentation of wort by yeast, through the action of the enzyme acetyltransferase (ATF). It has been found to be normally present in beer obtained by fermentation at a level of at least 2 mg / L, sometimes at least 3 mg / L, or even at least 4 mg / L, or at least 5 mg / L, or at least 6 mg / L, or at least 7 mg / L, or at least 8 mg / L, or at least 9 mg / L, or at least 10 mg / L. Consequently, AcHFA may be present in beer obtained by fermentation in quantities exceeding 1 mg / L, certainly exceeding 0.5 mg / L, and more certainly exceeding 0.25 mg / L. The inventors discovered that AcHFA is a negative foaming factor: it has a negative effect on foam stability. By adapting the frCELnn / Lznz / B / Yi fermentation process to decrease the amount of AcHFA in the final beer, foam stability can be increased by at least 10%, up to 40%. AcHFA (“hydroxyacetylated fatty acid”) is a C12-C22 fatty acid comprising a carboxylic acid group and a linear C11-C21 alkyl group, the alkyl group of which may be partially unsaturated, and which alkyl group is substituted with at least one hydroxy group and at least one acetate group. An acetate group (HiCCOa-) is abbreviated (as is common in the art) as ~OAc. AcHFA can be defined as structure 1: frCR Lnn / Lznz / E / Yi where n = is an integer that varies from 4-9, and where each , A, B, C and / or D can be equal or different, and where either a) is a single link, in which case: One of A and B is H, OH or OAc, and the other of A and B is H; One of C and D is H, OH or OAc, and the other of C and D is H; or b) is a double bond, in which case: one of A and B is H, while the other of A and B is not present (which means that the other of A and B is nothing), and one of C and D is H, while the other of C and D is not present (which means that the other of A and B is nothing); provided that in structure 1, at least one of all A, B, C, D is OH, and at least one of all A, B, C, D is OAc. As is commonly known, the double bond can have either a cis or trans configuration, although the cis configuration is preferred. Furthermore, as is common for organic acids, the acid group can be in its neutral form (as represented; -CO2H), but it can also be in ionic form (~CO2), or in salt form ((~CO2)XM), where M can be any metal ion, and preferably a metal ion available in beer, such as, for example, an ion of Na, K, Ca, Mg, Fe, Cu, Zn, or Mn, and where x = 1 if M is monovalent (Na or K), and where x can be 1, 2, or 3 for ions of higher valency. Carbon atoms bearing OH or OAc can independently have either the R or S configuration, although, preferably, adjacent carbon atoms bearing both an OH and an OAc group have either the R configuration, or both have the S configuration (RR and 55).Alternatively, one carbon atom of adjacent carbon atoms that bears an OH group and an OAc group has a 5 configuration, and the other carbon of the two adjacent carbon atoms has an R configuration (RS or SR). Preferably, AcHFA comprises a hydroxy group and an acetate group located on adjacent carbon atoms, optionally between multiple hydroxy and / or acetate groups. More preferably, AcHFA is a C16-C20 fatty acid (n = 6-8 in structure 1), and more preferably, a C18 fatty acid (n = 7 in structure 1). Much more preferably, AcHFA comprises one or two double bonds, and more preferably, one double bond. The double bonds are preferably located at the 6th, 9th, 12th, or 15th carbon atom, counting from the carboxylic acid group. More preferably, a double bond is located at the 9th carbon atom. In highly preferred embodiments, AcHFA is represented by structure 2: frCELnn / Lznz / B / Yi where: n = 1, 2, or 3, preferably 2 or 3, most preferably 3; m = 1 or 2, preferably 2; One of A and B is OH, and the other of A and B is OAc. Furthermore, for structure 2, the double bond can have either a cis or trans configuration (represented by the line format , which indicates that the orientation of a carbon-carbon single bond extending from a carbon-carbon double bond can be in either direction), although the cis configuration is preferred. The acid group in structure 2 can be in its neutral form, as shown, but it can also be in ionic form or as a salt, as defined above. In highly preferred embodiments, AcHFA is represented by structure 3: where one of A and B is OH, and the other of A and B is OAc. In these embodiments, AcHFA is (cis or trans', RR, SS, RS or SR) 12-acetoxy-13-hydroxyoctadec-9-enoic acid (3a), or (cis or trans', RR, SS, RS or SR) 13-acetoxy-12-hydroxyoctadec-9-enoic acid (3b): frCR Lnn / Lznz / E / Yi AcHFA has been found to occur naturally in beer, because it is formed during fermentation by the yeast enzyme acetyltransferase (ATF). An AcHFA precursor is a dihydroxy fatty acid, such as, for example, structures 1-3 defined above, where the AcHFA precursor has an OH group at each location where there is an OAc group in AcHFA. Yeast ATF enzymes acetylate (at least) one OH group to convert the AcHFA precursor to AcHFA. Furthermore, beer with reduced AcHFA content, compared to regular beer, has been found to have improved foaming properties. In particular, reducing the amount of AcHFA increases the stability of the beer's foam. In this context, beer foam stability is measured according to standards established by the NTBEM Institute and is expressed in seconds (s). Therefore, beer foam stability indicates the amount of time, in seconds, that the foam layer remains stable under standardized test conditions. The NIBEM methodology is generally known and can be found as EBC 9.42.1 analytical method. The test is performed at 20°C at atmospheric pressure. Foam stability is measured as the time elapsed from the preparation of the foam under standardized conditions (including a period during which the foam is allowed to drain) until the foam layer has decreased in height by 3 cm. Beer can refer to any type of beer, including, but not limited to, ale, porter, stout, lager, and bock. Beer is preferably a malt-based beer, that is, a beer prepared from the fermentation of wort made from malt. Preferably, beer is lager, which is a beer obtained by fermentation at 7–15°C using a bottom-fermenting yeast, followed by pressing at a low temperature. Lager includes, for example, pilsner. More preferably, a beer as described herein is a pilsner. A pilsner is a pale lager. In the present context, beer should be understood in a broad sense, encompassing both regular beer (containing alcohol) and low- or zero-alcohol (NA) beer. Therefore, beer in this context is preferably beer with an ethanol content of 0–15% by volume (ABV), preferably 1–15% by volume. Beer may be enriched with hops (hopped beer) or may not contain hops (hopped beer). Hopped beer includes beer brewed using modified hops, such as Rho hops. In a preferred embodiment, the beer is a regular beer. “Regular beer,” in this context, is beer brewed in a regular manner, obtained by a fermentation process that produces more than 1% ethanol by volume. Therefore, regular beer, as defined herein, has an ethanol content of more than 1% by volume, and preferably less than 15% by volume. The ethanol content of a regular beer is preferably from 2 to 15% by volume, more preferably from 2.5 to 12% by volume, and more preferably from 3.5 to 9% by volume. The regular beer is preferably a lager, as described above, and more preferably a pilsner. The expert in the technique is able to obtain regular beer, including regular lager and pilsner, for example, by the methods described in The Brewers Handbook (second edition), by Ted Goldammer (2008, Apex Publishers), or by the methods described in this document.Alternatively, regular beer can be obtained commercially. In another preferred embodiment, beer is a zero or low alcohol beer (NA beer). In this text, zero or low alcohol beer is a beer having an ethanol content of 1.0% by volume (ABV) or less, preferably 0.5% by volume or less, and more preferably 0.2% by volume or less. Therefore, NA beer is a beer having an ethanol content of 0-1.0% by volume, such as preferably 0-0.5% by volume. An NA beer can be obtained, for example, by dealcoholizing regular beer (a dealcoholized beer) or by restricted ethanol fermentation of the wort (a restricted fermentation beer). frCRLnn / Lznz / E / Yii One method for obtaining non-alcoholic beer as defined here is to subject a regularly brewed beer to a dealcoholization step, such as a rectification step, a reverse osmosis step, a dialysis step, or a freeze-concentration step, to remove ethanol from the fermented beer. These techniques are described, for example, in Brányik et al., J. Food. Ing. 108 (2012) 493-506, or in Mangindaan et al., Trends in Food Science & Technology, 71 (2018) 36-45. Another method for obtaining NA beer is to prepare the beer through a restricted fermentation process, which yields a restricted fermentation beer. A restricted fermentation beer is another type of NA beer as defined herein. A restricted fermentation beer is defined as a fermented beer obtained by the restricted ethanol fermentation of the wort. Restricted ethanol fermentation of the wort is fermentation that does not produce a significant net ethanol formation; that is, restricted fermentation as defined herein produces 1% by volume or less, preferably 0.5% by volume or less, and more preferably 0.2% by volume or less. Therefore, a restricted fermentation beer has an ethanol content of 1.0% by volume or less, preferably 0.5% by volume or less, and more preferably 0.2% by volume or less. Restricted must fermentation is a process in which the product obtained directly from fermentation has an ethanol content of 1.0% by volume or less, preferably 0.5% by volume or less, and more preferably 0.2% by volume or less. Those skilled in the art are familiar with various restricted fermentation techniques that do not produce a significant net ethanol yield. Examples include restricted ethanol fermentation of must characterized by: • a temperature below 7°C, preferably -1-4°C, such as -0.5-2.5°C, preferably for a period of 8-72 hours, more preferably 12-48 hours (“cold contact fermented beer”); and / or • a short fermentation time (e.g., less than 2 hours), the fermentation of which was rapidly stopped by temperature inactivation, such as by rapid cooling to -0.5-1°C, optionally followed by subsequent pasteurization (“stop-fermented beer”); and / or • fermentation by a yeast strain that produces low quantities of ethanol under the applied fermentation conditions, such as, for example, a yeast strain that produces less than 0.2 g of ethanol per gram of fermentable sugar in the wort, preferably less than 0.1 g of ethanol per gram of fermentable sugar.Suitable strains (e.g., Crabtree-negative strains) are known in the art, and the amount of ethanol produced under varying fermentation conditions can be determined by routine experiments (yeast-restricted beer); and / or fermentation using a first ethanol-producing yeast strain, in the presence of a sufficient quantity of a second ethanol-consuming yeast strain, such as Saccharomyces roux, to consume substantially all the ethanol produced by the first yeast strain; and / or wort with a fermentable sugar content such that a maximum of 1.0% by volume of alcohol is produced after fermentation is complete. In this case, the wort generally has a fermentable sugar content of less than 17.5 g / L, preferably less than 12 g / L, and more preferably less than 8 g / L (sugar-free wort beer). A restricted fermentation beer has not been subjected to a dealcoholization step to achieve the ethanol content of 1.0% by volume or less, preferably 0.5% by volume or less, more preferably 0.2% by volume or less. A person skilled in the art is aware of various suitable techniques for dealcoholizing a fermented beer (see above with reference to Brányik et al. and Mangindaan et al.), and none of these techniques has been applied to achieve the ethanol content. However, a restricted fermentation beer in the present context may optionally be subjected to a dealcoholization step to reduce the ethanol content obtained from fermentation from the 1.0% by volume or less, preferably 0.5% by volume or less, more preferably 0.2% by volume or less, to a lower ethanol content.However, preferably, a restricted fermentation beer as defined herein has not undergone any dealcoholization steps. A restricted fermentation beer in the present context is preferably a sugar-free wort beer, a restricted beer with yeast, a stopped fermentation beer, or a cold-contact fermented beer. In highly preferred embodiments, "beer" in this context means regular beer, restricted-fermentation beer, or a mixture of the two, preferably regular beer, cold-contact fermented beer, or a mixture of the two. More preferably, in this context, "beer" means regular beer having an ethanol content of 1-15% by volume, as defined above. In order to optimally benefit from the increased foam stability, a beer of the invention preferably has a low sugar content. The total sugar content of a beer of the invention, defined as the total of glucose, fructose, sucrose, maltose, and maltotriose, is preferably 0.05–5 g / 100 ml, more preferably 0.1–1 g / 100 ml, and even more preferably 0.15–0.5 g / 100 ml. This is because it has been found that in beer with a relatively low total sugar content, the foam-stabilizing effect of reduced amounts of AcHFA is stronger. frCRLnn / Lznz / E / Yii For similar reasons, a beer of the invention preferably has relatively high levels of free amino nitrogen (FAN). FAN contributes to foam stability, and the beer of the invention therefore preferably has an FAN content of 50-160 mg / L, preferably 90-140 mg / L, and more preferably 110-135 mg / L. Iso-alpha acids also have a positive effect on beer foam stability. Therefore, a beer of the invention preferably has a total iso-alpha acids content of 255 mg / L, preferably 5-45 mg / L, more preferably 10-30 mg / L, and more preferably 13-25 mg / L. Iso-alpha acids, in this context, are defined as the soft resin fraction of lupulin, which is produced in female hop cones. Alpha acids include, for example, humulone, cohumulone, and adhumulone. In order to obtain beer with a reduced amount of AcHFA as defined herein, three options are disclosed: removing AcHFA from the beer during or after fermentation, preventing AcHFA formation by using an ATF-deficient yeast for fermentation, and removing an AcHFA precursor from the fermenting mixture. The invention therefore discloses a method for increasing beer foam stability, comprising a wort fermentation step to obtain such beer, wherein: a) Fermentation is achieved using a yeast deficient in acetyltransferase (ATF); and / or b) the beer is brought into contact with an adsorbent capable of adsorbing AcHFA during or after fermentation; and / or c) the must has been subjected to a step of removal of an AcHFA precursor by an adsorbent capable of adsorbing the AcHFA precursor. ATF-deficient yeast. In a preferred embodiment, fermentation is achieved using an acetyltransferase (ATF)-deficient yeast (including any ATF ortholog), where such yeast is preferably S. cerevisiae. Such yeast can be obtained by genetic modification of the yeast (preferably S. cerevisiae), such as by replacement or alteration of the genes encoding ATF (knockout). An ATF-deficient yeast, in the present context, means that in yeast types where multiple copies of an ATF gene exist, preferably all copies of that ATF gene are knocked out. There are two genes associated with acetyltransferase activity: ATF-1 and ATF-2 (in S. cerevisiae). The ATF-1 gene has the gene identification number 854559 (NCBI database), and the ATF-2 gene has the gene identification number 853088 (NCBI database). In other yeast strains suitable for fermentation, the ATF genes of orthologs can be located using common knowledge. As mentioned, in ATF-1-deficient yeast, all copies of the frCR Lnn / Lznz / E / Yii ATF-1 gene are preferentially knocked out. In ATF-2-deficient yeast, all copies of the ATF-2 gene are preferentially knocked out. In one embodiment, the ATF-deficient yeast is ATF-1 deficient. ATF-1 deficiency results in approximately a 50–90%, and preferably approximately a 65–85%, reduction in AcHFA formation. In another embodiment, the ATF-deficient yeast is ATF-2 deficient. ATF-2 deficiency results in approximately a 10–40%, and preferably approximately a 30–10%, reduction in AcHFA formation. In preferred embodiments, the ATF-deficient yeast is at least ATF-1 deficient and, preferably, also ATF-2 deficient. In highly preferred embodiments, the ATF-deficient yeast is both ATF-1 and ATF-2 deficient. The use of a yeast that is deficient in both ATF-1 and ATF-2 achieves complete prevention of AcHFA formation during fermentation. ATF-deficient yeast can be obtained by commonly known methods, such as mutagenesis, preferably random mutagenesis, or by genetic engineering. Mutagenesis, as used herein, refers to a process by which at least one mutation is generated in the DNA of at least one yeast cell or its spore, thereby altering the genetic information of the yeast cells or spores. Thus, mutagenesis can result in ATF-deficient yeast as described above. As used herein, the term mutation refers to any change in the DNA of the yeast cell or spore, and includes, without limitation, point mutation, insertion or deletion of one or more nucleotides, substitution of one or more nucleotides, frameshift mutation, and single- or double-stranded DNA break, such as a chromosomal break or a subtelomeric break, and any combination thereof. Preferably, the mutation is located in an ATF gene, so as to produce ATF-deficient yeast as described above. Mutagenesis can be performed using any method known to the art, including conventional random mutagenesis methods such as radiation and chemical treatment, and recombinant DNA technologies such as site-directed mutagenesis or targeted mutagenesis. Therefore, in one embodiment, at least one yeast cell or spore of at least the first yeast species is subjected to treatment with UV irradiation, X-ray irradiation, gamma-ray irradiation, or a mutagenic agent, or genetic engineering. Genetic engineering is well known in the field and refers to the alteration of the genome of yeast cells or spores using biotechnology, so as to introduce an alteration of the DNA of a yeast cell or spore. frCR Lnn / Lznz / E / Yii “Random mutagenesis” refers to mutagenesis techniques in which the exact site of mutation is unpredictable and can occur anywhere on the chromosome of yeast cells or spores. Generally, these methods involve the use of chemical agents or radiation to induce at least one mutation. Random mutagenesis can also be achieved using error-prone PCR (polymerase chain reaction), where PCR is performed under conditions of low DNA polymerase copying accuracy, resulting in a relatively high mutation rate in the PCR product. Site-directed mutagenesis can be achieved using oligonucleotide-directed mutagenesis to generate site-specific mutations in a DNA sequence of interest.Targeted mutagenesis refers to mutagenesis methods that alter a specific or targeted gene in vivo, producing a change in genetic structure directed to a specific site, such as by programmable RNA-guided nucleases, such as TALEN, CRISPRCas, zinc finger nuclease, or meganuclease technology. In a preferred embodiment, mutagenesis is carried out in the method of the invention by subjecting at least one yeast cell or spore to treatment with radiation, such as UV irradiation, X-ray irradiation, gamma-ray irradiation, or a mutagenic agent, preferably a chemical agent such as NTG (N-methyl-N'-nitro-N-nitrosoguanidine) or EMS (ethylmethanesulfonate). Adsorption of AcHFA, or an AcHFA precursor. In a further preferred embodiment, the fermented beer is contacted with an adsorbent capable of adsorbing AcHFA. Additionally, the AcHFA precursor can be removed from the wort prior to fermentation by contacting the wort with an adsorbent capable of adsorbing the AcHFA precursor. It has been found that the same adsorbents can be used to remove the AcHFA precursor from wort and to remove AcHFA from beer during or after fermentation. That is, the AcHFA precursor and AcHFA itself are substantially adsorbed onto the same adsorbents. Suitable adsorbents include activated carbon, a hydrophobic adsorbent, a hydrophilic adsorbent, and a zeolite. Preferably, these adsorbents are applied during or after fermentation (preferably after fermentation) to adsorb AcHFA from the beer. To improve foam stability in hop-free beer, the beer can be contacted with any adsorbent suitable for adsorbing AcHFA (or a precursor thereof). Therefore, in preferred embodiments, the beer does not contain hops. Optionally, hops can be added to the beer later to further improve foam stability and achieve other advantages (flavor). Hop-containing beer contains iso-alpha acids, which have an additional stabilizing effect on the beer foam. frCELnn / Lznz / B / Yi To improve foam stability in hoppy beer, the beer is preferably contacted with an adsorbent that does not substantially adsorb iso-alpha acids. Iso-alpha acids are derived from hops during wort boiling and are known to have a foam-stabilizing effect. Those skilled in the art will appreciate that any adsorbent can be used for hoppy beer, provided it has a net effect on foam stability. This may depend on the amount of hops used and / or the amount of AcHFA formed during fermentation. In preferred embodiments, hoppy beer may be further spiked with hops after the AcHFA removal stage is complete. Activated carbon is well known in the art and can be used as an adsorbent to remove AcHFA and obtain a beer with reduced AcHFA according to the invention. However, a disadvantage of activated carbon is that it is not very efficient at removing AcHFA. Furthermore, activated carbon significantly adsorbs iso-alpha acids, which is a disadvantage in the treatment of hoppy beer. Another disadvantage is that activated carbon discolors the beer, resulting in an excessively pale beverage that is unappealing to consumers. Hydrophobic adsorbents include hydrophobic polymeric adsorbents, preferably polymeric adsorbents comprising aromatic and / or acyl groups. A person skilled in the art can readily determine, based on common knowledge and the methods described herein, which adsorbents are suitable for reducing AcHFA (or its precursor) from beer (or wort). One advantage of hydrophobic polymeric adsorbents is their high efficiency in removing AcHFA (or an AcHFA precursor). Furthermore, beer color is retained, and these adsorbents adsorb relatively little, or even none, of iso-alpha acids. Consequently, hydrophobic polymeric adsorbents, such as polystyrene / divinylbenzene (PS / DVB), for example, PLRP-S (marketed by Agilent), are preferred. Hydrophilic adsorbents are preferably hydrophilic polymeric adsorbents. A highly preferred hydrophilic adsorbent is a mixed cellulose ester adsorbent, for example, MCE (MF-Millipore™ membrane filters, Merck). This is the most efficient adsorbent among those evaluated, leaving the beer's color intact and not adsorbing iso-alpha acids. Furthermore, it can be regenerated, which, particularly for industrial beer production, leads to lower production costs and less waste material. Other preferred adsorbents are, for example, Supelclean™ adsorbents, such as, preferably, Supelclean LC C18, Supelclean LC C8, Supelclean LC Ph, Supelclean LC CN, or Supelclean LC SCX, more preferably, Supelclean LC C18, Supelclean LC C8, or Supelclean LC Ph, frCELnn / Lznz / B / Yi, and more preferably, Supelclean LC C18 and Supelclean LC C8. These adsorbents are preferred for the same reasons as those described above for MCE and PLRP-S. A zeolite, in the present context, is preferably a hydrophobic zeolite. This is a silicate-based molecular sieve containing S₁O₂ and Al₂O₃ in a molar ratio (S₁O₂:Al₂O₃) of at least 15. The term molecular sieve, as used herein, refers to a microporous material having pores with a diameter of no more than 2 nm. The term silicate-based means that the material contains at least 67% silicate by weight. A zeolite is therefore a microporous aluminosilicate. Zeolite adsorbents in the present context can be either natural or synthetic zeolites. It should be understood that hydrophobic silicate-based molecular sieves containing SIO2 and not Al2O3 satisfy the condition that the molecular sieve contains SIO2 and Al2O3 in the molar ratio of at least 15 (in which case, the zeolite is a microporous silicate, rather than a microporous aluminosilicate). According to a preferred embodiment, the adsorbent is a hydrophobic zeolite. The hydrophobic zeolite used in the present process preferably has a molar ratio of SiO2 / Al2O3 of at least 40, more preferably at least 100, even more preferably at least 200, and most preferably at least 250. The average pore size diameter of the hydrophobic zeolite is preferably in the range of 0.2–1.2 nanometers, more preferably 0.3–1.0 nanometers, even more preferably 0.4–0.8 nanometers, and most preferably 0.45–0.70 nanometers. The pore size diameter of the hydrophobic zeolite can be determined by analyzing the nitrogen adsorption isotherms at 77 K using the De Boer t-chart method. The surface area of ​​the hydrophobic zeolite is preferably at least 100 m² / g, more preferably 150 to 2000 m² / g, and most preferably 200 to 1000 m² / g. The surface area of ​​the hydrophobic molecular sieve can be determined by the BET method. The hydrophobic zeolite preferably has a mass-weighted average particle size in the range of 1 to 2000 micrometers, more preferably in the range of 10 to 800 micrometers, and most preferably from 100 to 300 micrometers. The particle size distribution of the hydrophobic molecular sieve can be determined using a set of sieves with different mesh sizes. The hydrophobic zeolite is preferably selected from ZMS-5 zeolite, Y-type zeolite, beta zeolite, silicalite, all-silica ferrierite, mordenite, and combinations thereof. More preferably, the hydrophobic zeolite is selected from ZMS-5 zeolite, Y-type zeolite, beta zeolite, and combinations thereof. More preferably, the hydrophobic zeolite is ZMS-5 zeolite. frCRLnn / Lznz / E / Yii The adsorbents for use as described in this document may be applied as known in the art. For the removal of AcHFA during fermentation, the fermentation mixture can be brought into contact with the adsorbent, for example, by passing the mixture over a column packed with the adsorbent, or by adding the adsorbent as a particulate material to the fermentation mixture and subsequently removing the adsorbent by filtration, cyclone, or other suitable technique. For the removal of AcHFA after fermentation, the fermented beer can be contacted with the adsorbent, for example, by passing the beer over a column packed with the adsorbent, or by adding the adsorbent as a particulate material to the beer and subsequently removing the adsorbent by filtration, cyclone, or another suitable technique. In preferred embodiments, the fermented beer is introduced into a holding tank, where it is contacted with the adsorbent for a period of, for example, 20 minutes to 24 hours, preferably 0.5 to 5 hours, to adsorb AcHFA. The AcHFA can then be removed by filtration. Alternatively, the beer can be continuously filtered over a filter loaded with the adsorbent. For the removal of an AcHFA precursor, the wort can be contacted with the adsorbent before fermentation, for example, by passing the wort over a column packed with the adsorbent, or by adding the adsorbent as a particulate material to the wort and subsequently removing the adsorbent by filtration, cyclone, or another suitable technique. Preferably, the wort is contacted as sweet wort, before arming. The skilled individual is familiar with numerous techniques for adsorbing an unwanted component from a liquid mixture, and any of these techniques can be applied to obtain beer with a reduced amount of AcHFA as defined here. Suitable techniques are described, for example, in C. Judson King, Separation Processes (2nd edition) McGraw-Hill, Inc. 1980. The wort, fermentation mixture, or beer is brought into contact with the adsorbent for a sufficient time to adsorb AcHFA, or its precursor. Those skilled in the art can easily determine this time based on common knowledge and the methods described here. Preferably, the contact time is from 5 minutes to 48 hours, more preferably from 0.5 to 24 hours, and even more preferably from 1 to 20 hours. Skilled workers can also easily determine the amount of adsorbent to use, based on common knowledge and the methods described in this document. Preferably, the adsorbent is used at a dosage of 0.001–10 g / L, more preferably 0.01–5 g / L, and most preferably 0.05–2.5 g / L. frCRLnn / Lznz / E / Yu Depending on the type and nature of the beer, the type and amount of adsorbent, and the contact time, the amount of AcHFA can be substantially reduced, as can be easily determined by an expert. The amount of AcHFA can be reduced by at least 50%, preferably by at least 75%, and more preferably by at least 80%. In some embodiments, the amount of AcHFA can be reduced to 90% or even 95% or more. In preferred embodiments where the AcHFA is removed from the beer by adsorption, the amount of AcHFA is reduced to less than 60% of the initial amount, more preferably to less than 20% of the initial amount, and more preferably to less than 5% of the initial amount. The effect of reducing AcHFA is that foam stability increases by at least 10 seconds, preferably at least 15 seconds, and more preferably at least 20 seconds. Foam stability can be increased to 40 seconds, or even 50 seconds or more. In highly preferred embodiments, the invention relates to a method for increasing beer foam stability, comprising contacting fermented beer with an adsorbent capable of adsorbing AcHFA. The adsorbent and the method of contacting the beer with the adsorbent are as defined above. This results in beer with increased foam stability, as described above. For the sake of clarity and concise description, the features are described herein as part of the same or separate embodiments; however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the described features. The invention will now be further illustrated by the following non-limiting examples. Methods. Analysis of AcHFA. The AcHFA content in beer can be analyzed by LC-MS (liquid chromatography-mass spectrometry). The LC-MS system consisted of a Waters TQ-S mass spectrometer and a Waters Acquity UPLC system. The mobile phase consisted of: A: Milli-Q water + 0.1% (v / v) formic acid B: acetontril + 0.1% (v / v) formic acid The analytical column was a 15 cm * 2.1 mm DI UPLC BEH C18 (1.7 µm) column. AcHFA was separated from the other matrix constituents with the following gradient: T 0 min: 95% A, 5% B T 13 min: 70% A, 30% B T 17 min: 5% A, 95% B frCRLnn / Lznz / E / Yi T25 min: 95% A, 5% B The flow rate was set to 0.25 mL / min, and the column temperature was adjusted to 50°C. The UPLC system was connected to the MS via an electrospray interface (ESI) operating in negative ion mode. MRM data were recorded for the following transition: m / z 355 > 295. The cone voltage was set to 40 volts. The collision energy was set to 15 eV. AcHFA was detected as the compound represented by structure 3. The amount of AcHFA was expressed in arbitrary units (au), which are derived from the peak area of ​​the chromatogram to provide quantitative results. Determination of sugar content in beer. Sugar content was measured using ultra-performance liquid chromatography (UPLC). UPLC can be performed effectively at 65°C. A suitable eluent is an acetonitrile / water mixture, for example, in a 75 / 25 volume ratio. The detector typically used is a refractive index (RI) detector. The sugar content of a sample was determined by comparing the UPLC curve of the sample with calibration curves from standard samples with known sugar concentrations. The samples for UPLC were prepared as follows. A beer or wort sample was diluted by a factor of 5 by adding a 50 / 50 acetonitrile / water mixture (equal parts by volume). If present, CO2 was removed before dilution (e.g., by swirling or shaking the sample). After dilution, the sample was filtered to obtain a clear solution. The filtered sample was injected into the UPLC at 65°C using the aforementioned eluent. Determination of free amino nitrogen (FAN). The amount of free amino nitrogen (such as amino acids, small peptides, and ammonia) was measured according to the nitrogen method using the o-phthaldialdehyde assay (OPA). The OPA method was performed using a photometric analyzer (e.g., the Galleiy™ Plus photometric analyzer). According to the OPA method, a test sample is treated with ortho-phthaldialdehyde (OPA) and N-acetylcysteine ​​(NAC). This treatment results in the decomposition of primary amino groups present in the test sample through the formation of isoindoles. The isoindole content is then determined using the photometric analyzer at a wavelength of 340 nm. The free amino nitrogen (expressed in mg FAN / L) can be calculated based on the measured isoindole content.If necessary, the beer or wort sample is first subjected to centrifugation to clarify the sample, and / or a CO2 removal stage (e.g., by stirring or shaking the sample) before analysis. Determination of ethanol in beer. The ethanol content was measured using a photometric analyzer (e.g., the Gallery™ Plus photometric analyzer). The test sample was subjected to an enzymatic method in which the ethanol present in the sample was converted to acetaldehyde using alcohol dehydrogenase (ADH). The acetaldehyde content was then determined using the photometric analyzer at a wavelength of 340 nm. The ethanol content could be calculated based on the acetaldehyde content. If necessary, the beer or wort sample was first subjected to centrifugation to clarify the sample, and / or a CO₂ removal step (e.g., by stirring or shaking), before analysis. Determination of alpha acids in beer. Iso-alpha acids were quantitatively determined using EBC 9.47 2010: reduced iso-acids and isoα-acids (Rho, Tetra, Hexa) in beer by HPLC (high performance liquid chromatography). Determination of foam stability. Foam stability is determined in accordance with standards set by the NIBEM Institute, EBC 9.42.1. Degassing and recarbonation.. All experiments with AcHFA adsorption from beer were performed on regular beer that had been degassed. Before measuring foam stability, the beer was recarbonated. The degassed beer was obtained as follows: Approximately 200 ml of bottled beer (4°C) were carefully transferred (avoiding foaming) to clean 500 mL laboratory bottles. The bottles containing the samples were placed in a water bath at 20°C and gently shaken (40 rpm) for 40 minutes. Next, the agitation speed was increased to 120 rpm, and agitation continued for 30 minutes to degas the beer. Throughout the degassing process, the headspace of the bottles was continuously flushed with nitrogen gas to prevent oxidation of the beer. Recarbonation was achieved on a laboratory scale as follows. Stainless steel Millipore vessels (Millipore model, catalog no. xx6700p05) were prepared for use as regular beer kegs. The kegs were cleaned and flooded with CO2 to remove air before adding the beer. Beer samples of approximately 1–2 liters were transferred to the kegs, and the samples were subjected to 2500 kPa (2.5 bar) of CO2 pressure while being agitated at 100 rpm for 30 minutes. The entire procedure was performed at 20°C. CO2 pressure was used to dispense the beer using a lance positioned approximately 0.7 cm from the bottom of the vessel. The foam was then prepared by connecting the Nibem foam dispenser to the keg (pressurized with CO2), similar to the process used for bottled beer. Foam stability was determined according to Nibem's described method. Example 1. Removing AcHFA from beer achieves foam stabilization. The degassed beer was incubated with 0.1 g / L commercial methyl cellulose ester adsorbent (MCE, MF-Millipore™ membrane filters, Merck) for 16 hours at room temperature. The beer was then filtered through a 0.2 µm filter and recarbonated. The results show that adsorbing AcHFA onto MCE and subsequently removing AcHFA from the beer results in a beer with greater foam stability. Blank beer underwent the same procedure, except for the adsorption step. After treatment, the AcHFA content in the treated beer was reduced to 6.3% of the amount in the regular beer. The blank beer had a foam stability (NIBEM) of 253 seconds, while the MCE-treated beer had a foam stability of 296 seconds. Therefore, removing more than 90% of the AcHFA resulted in a 17% increase in foam stability. The AcHFA removal process has been shown to efficiently remove AcHFA from both hopped and unhopped beer (data not shown). Furthermore, MCE has been found not to significantly adsorb iso-alpha acids, and the beer color remains unaffected. This is advantageous, as the presence of iso-alpha acids has an additional stabilizing effect on beer foam. Therefore, MCE is a highly preferred adsorbent. Example 2. AcHFA is a negative foaming factor. Regular degassed beer was obtained as described in Example 1. The beer in this case was a full malt beer without hops. The degassed beer was incubated for 16 hours at room temperature with 0.2 g / L of PLRP-S (Agilent) to achieve complete AcHFA removal and obtain an AcHFA-free, hop-free beer. The adsorbent was filtered and isolated, then washed with acetonitrile to obtain crude AcHFA. The crude AcHFA was fractionated on a reversed-phase HPLC column (C18) using a water-to-acetonitrile gradient. The resulting fractions were evaluated for their effect on foam stability by addition to beer, and the negative foam fractions were collected and analyzed by LC-MS and characterized by NMR as AcHFA according to the definition in the description. Thus, pure AcHFA was isolated and characterized. To the degassed beer with hops and degassed beer without hops, with regular amounts of AcHFA obtained by conventional fermentation, an additional amount of pure AcHFA was added. frCRLnn / Lznz / E / Yii After gentle homogenization and recarbonation as described in Example 1, the foam stability was determined as described. The amount of AcHFA added is shown in Table 1 and represented in Figures 2a and 2b. Table 1. frCRLnn / Lznz / E / Yu Beer foam stability (sec) Beer foam stability (sec) Hopped beer 271 Unhopped beer 202 + 0.25 mg / L AcHFA 270 + 1.5 mg / L AcHFA 198 + 0.5 mg / L AcHFA 268 + 2.0 mg / L AcHFA 194 + 1.0 mg / L AcHFA 263 + 4.0 mg / L AcHFA 162 + 2.0 mg / L AcHFA 251 + 4.0 mg / L AcHFA 233 The results show that as the amount of AcHFA in regular beer increases, the beer's foam stability decreases rapidly. Therefore, it has been concluded that AcHFA is a negative foam factor, and that beer with lower amounts of AcHFA has greater foam stability. Example 3. Beer with a reduced amount of AcHFA has greater foam stability. In another experiment, hoppy beer without AcHFA and unhopped beer without AcHFA were obtained by incubation for 16 hours at room temperature with PLRP-S (Agilent) at 0.2 g / L to achieve complete AcHFA removal. Before the addition of AcHFA to the hoppy beer, the loss of iso-alpha acids during the adsorption stage was compensated for by the addition of 20 mg / L of iso-alpha acids (IAA, B-hop, Hopsteiner). Both AcHFA beers were subsequently degassed. AcHFA was added in varying amounts to AcHFA-free beers. After gentle homogenization and recarbonation as described above, foam stability was determined. The results are shown in Table 2 and Figures 3a and 3b. Table 2, Beer foam stability Beer foam stability Hop beer (AcHFA free) 261 Hop-free (Regular AcHFA) 200 Hop beer (+IAA), AcHFA free 317 Hop-free (AcHFA free) 261 Hop beer (+IAA) + 0.25 mg / L AcHFA 306 Hop-free + 0.25 mg / L AcHFA 251 Hop-infused beer (+IAA) + 0.5 mg / L AcHFA 298 Hop-free + 0.5 mg / L AcHFA 234 Hop-infused beer (+IAA) + 0.75 mg / L AcHFA 295 Hop-free + 0.75 mg / L AcHFA 227 Hop-infused beer (+IAA) + 1.0 mg / L AcHFA 285 Hop-free + 10 mg / L AcHFA 221 Hop-infused beer (+IAA) + 1.5 mg / L AcHFA 273 Hop-free + 1.5 mg / L AcHFA 214 frCRLnn / Lznz / E / Yii The results show that decreasing the amount of AcHFA in beer below the levels found in regular beer leads to an increase in foam stability in a manner dependent on the AcHFA concentration. Beer without AcHFA exhibits the greatest foam stability. Example 4. Reduction of AcHFA in beer A regular (hopped) beer was obtained with a conventional amount of AcHFA. This beer was degassed as described and contacted in 30 ml portions (10 column volumes) with the same amount of various Supelclean™ adsorbents (Sigma Aldrich) on a 3 ml SPE column, and subsequently recarbonated. The results are shown in Table 3 and Figure 4. Table 3, sample AcHFA (ua) % of initial Hop-free white 870 100% + LC WCX 815 94% + LC Si 815 94% + LCC18 25 3% + LC C8 25 3% + LC Ph 140 16% + LCCN 330 38% + LC SAX 680 78% + LC SCX 470 54% The results show that a variety of hydrophobic and hydrophilic adsorbents are capable of reducing the amount of AcHFA in beer. The preferred adsorbents are LC C18, LC C8, and LcPh. In preferred embodiments, AcHFA is reduced to less than 60% of the initial amount, more preferably to less than 20% of the initial amount, and even more preferably to less than 5% of the initial amount. Example 5. Reduction of AcHFA in beer using PLRP-S and activated carbon. The degassed, hop-free beer was exposed to PLRP-S (0.1 mg / L) and 1.0 mg / L of activated carbon (Aktivkohle, art. 2186 Merck), and subsequently re-carbonated. The results are shown in Figure 5. The results show that PLRP-S is more efficient at removing AcHFA from beer. Furthermore, activated carbon was observed to remove beer color, which is considered a disadvantage. PLRP-S leaves the beer color intact. Additionally, PLRP-S does not significantly adsorb iso-alpha acids. Therefore, PLRP-S (and MCE, see Example 1) are preferred adsorbents over activated carbon. Example 6. Removal of AcHFA precursor from sweet wort, to obtain beer with a reduced amount of AcHFA in relation to conventional beer. In a conventional brewing process at a pilot plant, the sweet wort was treated with PLRP-S by coating a PVPP filter installed between the lauter tun and the wort tank with 750 g of PLRP-S, and treating 15 hl of sweet wort with this filter before it entered the wort tank (Figure 6). Subsequently, the beer was prepared conventionally (hop addition, boiling, whirlpooling, fermentation, post-treatment, and bottling). From the same wort, a comparative beer was prepared using the same process conditions, but without filtering the sweet wort over the filter loaded with PLRP-S. The amount of the AcHFA precursor (a dihydroxy fatty acid) was analyzed in a sample of the hopped wort (annion wort) using HPLC conditions as described for AcHFA. The amount of AcHFA was determined in the final beer. The results are shown in Table 4. frCALnn / Lznz / E / Yi Experimental Blank foam stability (sec) 270 288 total iso-α-acids (mg / L) 18.4 18 precursor AcHFA in wort (ua) 22900 6530 AcHFA in beer (ua) 25900 5790 The results show that by removing the AcHFA precursor through adsorption, AcHFA formation in the final beer can be prevented. This results in increased foam stability in the resulting beer. Furthermore, the results show that the adsorption process can be applied on an industrially relevant scale. Example 7. Obtaining beer with a reduced amount of AcHFA by modifying the yeast. In this example, a wild-type (WT) yeast deletion library of S. pastorianus was constructed with different combinations of deleted ATF1 and ATF2 alleles using CRISPR-Cas9 technology. S. pastorianus WT contains five copies of ATF1 and four copies of ATF2, from both the S. cerevisiae and S. eubayanus genomes. With the CRISPR-Cas9 system functional in S. pastorianus, all copies of a gene are targeted in a single transformation. Ultimately, nine ATF1 / 2 genes were deleted from four different chromosomes in just two transformations. ATF-1-deficient yeast is designated strain a. ATF-2-deficient yeast is designated strain b. ATF-1- and ATF-2-deficient yeast is designated strain c. The impact of various knockouts was studied by culturing the strains under brewing-relevant conditions.The strains showed similar growth rates, sugar consumption profiles, and ethanol production during a standard beer fermentation in wort at 15° Plato. Obtaining wild-type yeast mutants. The mutant strains were obtained following the methodology described in CRISPR-Cas9-mediated gene deletions in lager yeast Saccharomyces pastorianus, Arthur R. Gorterde Vries et al., Microb Cell Faci (2017) 16: 222. An exhibit of the mutations is shown in Figure 7a. Characterization of WT with ATF deletions under brewing conditions. To verify the fermentation performance, the strains were inoculated into 15° Plato must that had been autoclaved and filter-sterilized, with added zinc to meet the yeast growth requirements. Three bottles per strain were inoculated with the same cell concentration of approximately 5 million cells. Samples were taken from all bottles at the beginning of the experiment and after seven days of fermentation for HPLC analysis. However, one bottle from each triplicate was also sampled during fermentation to monitor sugar consumption and the production of glycerol, ethanol, and biomass, for comparison with fermentation using water-based wort (WT). After fermentation, the supernatant from each bottle was analyzed by HPLC to determine the sugar, glycerol, and ethanol content.The mutant strains were observed to exhibit substantially identical behavior when applied in fermentation compared to wild-type yeast. The sugar consumption profile over time for glucose, maltose, maltotriose, and fructose indicates a substantially identical consumption pattern. Furthermore, glycerol and ethanol production, as monitored during fermentation, was substantially identical. Similarly, the cell growth rate (measured by optical density) was substantially identical. An exemplary figure showing the ethanol production of strains a, b, and c is included as Figure 7b. In all parameters evaluated, the mutant strains showed substantially identical characteristics and a substantially identical time course. Therefore, the mutant strains could be applied in existing production processes to decrease the amount of AcHFA in the final beer. Therefore, ATF-deficient yeast strains were obtained that could be used under the same conditions as WT yeast. ATF-1 deficient yeast (strain a), ATF-2 deficient yeast (strain b), and yeast deficient in both ATF-1 and ATF-2 (strain c) were used in a standard wort fermentation to evaluate their activity in a standard brewing process. The different yeasts (5 million cells / ml inoculated) were fermented in 150 ml of 15–16P wort with whole malt hops in 250 ml infusion flasks, shaken at 200 rpm, at 13°C for 7 days under microaerobic conditions. The resulting beer was compared to beer brewed with unmodified WT yeast. The results are shown in Table 5. frCRLnn / Lznz / E / Yii Table 5: yeast types AcHFA (ua) % relative to WT WT wild type (WT) 28200 100 strain a deletion ATF 1 4155 15 strainb deletion ATF2 21800 77 strain c deletion ATF 1 + ATF2 nd 0 The results show that when using an ATF-1-deficient yeast, AcHFA is reduced to 15% of the amount of AcHFA observed using a wild-type yeast. With an ATF-2-deficient yeast, AcHFA is reduced to 77% of the amount of AcHFA observed using a wild-type yeast. By using a yeast that is deficient in both ATF-1 and ATF-2 (preferably all copies), AcHFA formation can be completely suppressed. Example 8. Removal of AcHFA from regular beer on an industrially relevant scale, to obtain beer with a reduced amount of AcHFA. The beer was brewed in a pilot plant using a conventional process and conventional yeast. The brewing process produced lager beer. Lager beer with added iso-alpha acids (IAAs) (20 mg / L of B-hop, Hopsteiner) was obtained, as well as beer without added iso-alpha acids. The lager beer was filtered and stabilized with PVPP, then stored in a holding tank where it was contacted with 0.1 g / L of PLRP-S (Agilent) for one to two hours. The beer was then filtered to remove the PLRP-S and adsorbed AcHFA (Figure 8a). Alternatively, the beer obtained from fermentation could be filtered over a PLRP-S coated filter to remove AcHFA (Figure 8b; data for the resulting beer are not shown, but are comparable to those for the beer obtained by the process shown in Figure 8a). The amounts of AcHFA were analyzed and compared with the amount in beer without this filtration step. In addition, the foam stability of the resulting beer was compared. The results show that treating the beer obtained from fermentation with PLRP-S for one or two hours significantly reduced the amount of AcHFA. This had a significant and positive effect on foam stability, both in beer with added iso-alpha acids and in beer without added iso-alpha acids. Therefore, adsorbents such as PLRP-S can be used to remove AcHFA and increase foam stability in beer.

Claims

CLAIMS 1. A beer, comprising less than 2 mg / 1 of AcHFA, wherein AcHFA is a C12-C22 fatty acid, comprising a carboxylic acid group and a linear C11-C21 alkyl group, wherein said alkyl group may be partially unsaturated, and wherein said alkyl group is substituted with at least one hydroxy group and at least one acetate group.

2. A beer according to claim 1, wherein AcHFA is defined by the structure frCELnn / Lznz / B / Yi where n = is an integer ranging from 4-9, and wherein each of A, B, C and / or D may be the same or different, and wherein either a) is a single bond, in which case: one of A and B is H, OH or OAc, and the other of A and B is H; one of C and D is H, OH or OAc, and the other of C and D is H; ob) is a double bond, in which case: one of A and B is H, while the other of A and B is not present, and one of C and D is H, while the other of C and D is not present; provided that in structure 1, at least one of all of A, B, C, D is OH, and at least one of all of A, B, C, D is OAc.

3. A beer according to claim 1 or 2, wherein AcHFA is defined by structure 2: wherein η = 1, 2, or 3, preferably 2 or 3, more preferably 3; m = 1 or 2, preferably 2; one of A and B is OH, and the other of A and B is OAc.

4. A beer according to any of claims 1-3, comprising 0-15% by volume of ethanol.

5. A beer according to any of claims 1-4, comprising less than 1.5 mg / 1 of AcHFA, preferably less than 1.0 mg / 1, more preferably less than 0.5 mg / 1, even more preferably less than 0.25 mg / 1.

6. A beer according to any of claims 1-5, comprising a total of 5-55 mg / 1 iso-alpha-acids.

7. A beer according to any of claims 1-5, comprising a total sugar content, defined as the total glucose, fructose, sucrose, maltose and maltotriose, of 0.05-5 g / 100 ml.

8. A method for increasing the stability of beer foam, comprising a wort fermentation step to obtain said beer, wherein: a) the fermentation is achieved using an acetyltransferase (ATF) deficient yeast; and / ob) the beer is contacted with an adsorbent capable of adsorbing AcHFA during or after fermentation; and / oc) the wort has been subjected to a step of removing an AcHFA precursor by an adsorbent capable of adsorbing the AcHFA precursor.

9. A method according to claim 8, wherein the adsorbent is an activated carbon, a hydrophobic adsorbent, a hydrophilic adsorbent, or a zeolite.

10. A method according to claim 8 or 9, wherein the adsorbent is activated carbon, a polystyrene / divinylbenzene adsorbent, a mixed cellulose ester adsorbent, or a hydrophobic zeolite, preferably a polystyrene / divinylbenzene adsorbent, a mixed cellulose ester adsorbent, or a hydrophobic zeolite.

11. A method according to any of claims 8-10, comprising contacting a fermentation-produced beer with an adsorbent, preferably a polystyrene / divinylbenzene adsorbent, a mixed cellulose ester adsorbent, or a hydrophobic zeolite, capable of adsorbing AcHFA.