A fermentation process and fermented beverage produced thereby

Abstract

A method of fermenting a high gravity wort comprising: providing a wort (preferably at least 18°P) comprising zinc at at least 100 ppb and, preferably, an ammonium salt, wherein the wort has a free am

Description

FIELD OF THE INVENTION The present invention is directed to method of fermenting a high gravity wort, which may have an original gravity of at least 18°P, and a fermented beverage, preferably a beer, produced using the method. BACKGROUND TO THE INVENTION There is a desire in the brewing industry to produce beer at higher and higher gravity, primarily due to the increase in volumetric productivity, reduced capital costs, and lower energy input required that it provides. Fermentation, which is a step of the brewing process, presents specific challenges when attempting to perform it at high gravity. For example, the increased viscosity of the wort can affect the mixing of yeast and oxygen in the wort, impacting the length and efficiency of fermentation and the flavour profile of the resulting fermented beverage. Furthermore, the increased osmotic pressure and the reduced concentration of yeast nutritional factors in the wort and the increased production of alcohol (which is toxic to yeast) during high gravity fermentation increase the stress that is placed on the yeast. These factors may reduce the number of fermentation cycles in which the yeast can be used. This said, a certain degree of yeast stress can be beneficial to the flavour profile of the fermented beverage because it can result in higher amounts of sulfur dioxide (which improves flavour stability in the fermented beverage as an antioxidant) and higher quantities of esters, which impart fruity notes. In view of the above, there is a need for fermentation processes that address the specific challenges of high gravity fermentation while providing fermented beverages having desirable organoleptic properties. The present invention aims to address one or more of the problems encountered when fermenting at high gravity. SUMMARY OF THE INVENTION The present invention is directed to a method of fermenting a wort that is optimised for fermenting at high gravity. Viewed from a first aspect, the present invention is directed to a method of fermenting a high gravity wort comprising: (a) providing a wort comprising zinc in an amount of at least 100 ppb and, optionally, an ammonium salt in an amount of at least 1 ppm nitrogen / °P, wherein the wort has a free amino nitrogen content of at least 10 ppm FAN / 'P; (b) adding the wort to a fermentation vessel at a temperature below 11 °C and, during the step of adding, pitching a yeast into the wort and contacting the yeast with oxygen for at least 2 hours; (c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase; (d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached: (i) a peak yeast cell count; (ii) a minimum FAN concentration; (iii) a minimum pH; (iv) an apparent extract of at least 5°P; and, (v) a residual fermentable sugar concentration of at least 4 °P; (e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and, (f) cooling the wort to less than 4°C to provide a fermented wort. Viewed from a second aspect, the present invention is directed to a fermented beverage prepared by the process of the present invention. Further beneficial features of the invention are set out herein below and in the dependent claims. BRIEF DESCRIPTION OF THE FIGURES Figure 1a shows a yeast cell count during a number of fermentation processes. The dashed line indicates the peak yeast cell count. Figure 1b shows a temperature profile of the fermentation processes described in Figure 1a. The dashed line corresponds to that of Figure 1a, i.e. the peak yeast cell count. Figure 1b shows that increasing the temperature of the fermenting wort at the peak yeast cell count shortens the fermentation time. Figure 1c shows the total butanedione (diacetyl) content during the fermentation process described in Figures 1a and 1b. Figure 1c shows that increasing the temperature of the fermenting wort at the peak yeast cell count shortens the time taken to reach a desirable total diacetyl concentration. Figure 1d shows the variation of yeast cell count, FAN concentration, and pH during fermentation as a function of apparent extract. Figure 2a shows the fermentation process described in Example 1, including the temperature and apparent extract levels during fermentation. Figure 2b shows the fermentation process described in Example 1, including the temperature, apparent extract, pressure and yeast cell count levels during fermentation. Figure 2c shows the fermentation process described in Example 1, including the temperature, acetaldehyde concentration, total diacetyl (butanedione), and total pentanedione levels during fermentation. Figure 3 shows the fermentation process described in Example 2, including the temperature and apparent extract levels during fermentation. Figure 4a shows the fermentation process described in Example 3, including the temperature and apparent extract levels during fermentation. Figure 4b shows the fermentation process described in Example 3, including the temperature and apparent extract levels during fermentation. Figure 5 shows the effect of adding a 32°P glucose solution at 24 hours (After 24h), 48 hours (After 48h), 72 hours (After 72h) and 96 hours (After 96h) after the step of adding the wort was completed on apparent extract during fermentation, compared to a control where the sugar solution was added at the start before pitching the yeast (At 20P). DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method of fermenting a wort at high gravity that optimises one or more of the following: • The composition of the wort, to ensure that the yeast has sufficient nutritional factors for high gravity fermentation; • The timing and duration of yeast contact with oxygen or oxygenated / aerated wort, to ensure that sufficient oxygen is provided for yeast cell growth while maintaining a desirable flavour profile; and, • The fermentation conditions, to ensure quick and efficient fermentation. The present invention may allow the yeast to be reused in multiple fermentation cycles, for example at least 5 fermentation cycles, preferably 7 to 15 fermentation cycles. With the above in mind, the present invention is directed to a method of fermenting a high gravity wort comprising: (a) providing a wort comprising zinc in an amount of at least 100 ppb and, optionally, an ammonium salt in an amount of at least 1 ppm nitrogen / °P, wherein the wort has a free amino nitrogen content of at least 10 ppm FAN / °P; (b) adding the wort to a fermentation vessel at a temperature below 11 °C and, during the step of adding, pitching a yeast into the wort and contacting the yeast with oxygen for at least 2 hours; (c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase; (d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached: (i) a peak yeast cell count; (ii) a minimum FAN concentration; (iii) a minimum pH; (iv) an apparent extract of at least 5°P; and, (v) a residual fermentable sugar concentration of at least 4 °P; (e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and, (f) cooling the wort to less than 4°C to provide a fermented wort. Providing the wort The wort may be prepared by methods known to the skilled person. It may be prepared from a mix of malted barley and adjunct grains, e.g. corn or rice, or it may be a pure malt wort. The wort may be provided at high gravity, which may be at least 15°P, preferably from 16 to 30°P. In embodiments, the gravity may be at least 18°P, preferably from 18 to 30°P, more preferably from 18 to 25°P, for example 18, 19, 20, 21,22, 23, 24, or25°P. In a variation of the method, which is discussed hereinbelow, the wort gravity may be increased during or after step b) by the addition of a solution comprising one or more fermentable sugars. Yeast nutritional factors may be added to the wort to prepare the yeast for fermentation at high gravity. Accordingly, the wort comprises zinc in an amount of at least 100 ppb and may comprises zinc in an amount of from 100 to 2000 ppb, preferably from 100 to 500 ppb, even more preferably from 150 to 250 ppb, for example 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, or 250 ppb. Additionally, an ammonium salt may be added to the wort, preferably one or more selected from the group consisting of ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium phosphate. The wort may comprise the ammonium salt in an amount of at least 5 g / hL, preferably from 10 to 30 g / hL, for example 10, 15, 20, 25, or 30 g / hL. The wort may comprise the ammonium salt in an amount of from 0.1 to 5 ppm nitrogen / °P, preferably from 0.5 to 3 ppm nitrogen / °P, more preferably from 1 to 2 ppm nitrogen / °P, for example 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 ppm nitrogen / °P. The unit “nitrogen / °P” is the proportion of the ammonium salt’s molecular weight that is nitrogen divided by the gravity of the wort in degrees Plato. For example, 6900 hL of a 20.8°P wort may be dosed with 18 g / hL (180 ppm) of ammonium sulfate. The nitrogen content of ammonium sulfate is 21%, so the nitrogen content is 38 ppm@20.8°P, or 1.8 ppm nitrogen / °P. The addition of nutritional factors may increase the number of fermentation cycles in which the yeast can be used. The wort has a free amino nitrogen (FAN) concentration of at least 10 ppm / °P, preferably from 10 to 16 ppm / °P, for example 10, 11, 12, 13, 14, 15, or 16 ppm / °P. This may be achieved by supplementing the wort with an ammonium salt as described above. The wort may be provided with a dissolved oxygen concentration, which may be from 1 mg / L to 35 mg / L, preferably from 1 to 25 mg / L, more preferably from 1 to 10 mg / L for example 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mg / L. The dissolved oxygen concentration may be achieved by aerating the wort using air or oxygen by methods known to the skilled person. Preferably the wort is aerated with air because the nitrogen in the air may remain as bubbles in the wort. These can aid mixing of the wort, yeast and oxygen as they disperse, which can be particularly beneficial in a viscous high gravity wort. Adding the wort to a fermentation vessel The wort may be added to the fermentation vessel (also known as filling) by piping it from a wort tank to the fermentation vessel. The wort may be added continuously or discontinuously. The aeration of the wort with air or oxygen may occur in-line while this piping is taking place. The fermentation vessel is preferably a cylindro-conical tank (CCT) fermentation vessel. The fermentation vessel preferably has a height to diameter ratio of at least 1.5:1, preferably from 2:1 to 4:1, for example 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. This may result in improved mixing of the yeast and oxygen in the wort, a particular benefit in a viscous high gravity wort. The wort may be cooled for the step of adding to the fermentation vessel. The wort is added to a fermentation vessel at a temperature below 11 °C, preferably from 6 to 11 °C, preferably from 8 to 11 °C, for example 8, 9, 10, or 11 °C. Adding the wort at these temperatures may improve the dissolution of oxygen in the wort. Pitching the yeast Yeast is added (pitched) in to the wort during the step of adding the wort to the fermentation vessel. The present inventors have found that pitching the yeast while adding the wort to the fermentation vessel can improve the mixing of the yeast and oxygen in the wort. The amount of yeast added to the wort (also known as the pitching rate) may be higher to account for the increased carbohydrate concentration at high gravity. The yeast may be pitched at a rate of at least 1 million cells / mL / °P, preferably from 1.2 to 2 million cells / mL / °P, for example 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 million cells / mU°P. The yeast may be any of those known to the skilled person to ferment wort to provide a fermented beverage, in particular a beer, for example Saccharomyces cerevisiae or Saccharomyces pastorianus. The timing of the pitching of the yeast during the adding of the wort to the fermentation vessel may be important for achieving the most efficient mixing of yeast and oxygen in the wort. Accordingly, the yeast may be pitched after at least 30% of the wort, preferably from 30 to 90%, more preferably from 40 to 60% for example 40, 50, or 60% of the wort has been added to the fermentation vessel; or at least 50% of the wort, preferably from 50 to 90% for example 50, 60, 70, 80, 90, or 100% of the wort has been added to the fermentation vessel; or at least 70% of the wort, preferably from 70 to 90% for example 70, 80, 90, or 100% of the wort has been added to the fermentation vessel. Aeration / oxygenation of the yeast The present inventors have discovered that the aeration / oxygenation of the yeast can be particularly important when fermenting at high gravity. Oxygen is one of the most important growth factors for yeast because it is essential for the synthesis of yeast membrane lipids, in particular sterols, which are vital for yeast cell proliferation. However, the present inventors have discovered that the length of contact between the yeast and oxygenated wort may be more important than its dissolved oxygen concentration. Without wishing to be bound by theory, the present inventors understand that yeast has a high affinity for oxygen and that the maximum rate of lipid synthesis can be achieved with a very low dissolved oxygen concentration, for example less than 0.1 mg / L, or even less than 0.001 mg / L. However the lipid production can take time to complete, including their synthesis, storage in membranes and reserve vesicles and the building-up of healthy mitochondria. The present inventors understand that the yeast should be in contact with oxygenated wort for the period of this production. According to the above, in the present invention, the yeast is contacted with oxygen for at least 2 hours during the step of adding the wort to the fermentation vessel. Preferably, the yeast is contacted with oxygen or oxygenated wort for from 2 to 15 hours, more preferably from 2 to 10 hours, for example from 2 to 5 hours. It is preferred that this occurs during the adding of the wort to the fermentation vessel in order to improve mixing of the wort, yeast and oxygen. The contact of the yeast with oxygen may occur immediately after pitching is completed. Accordingly, between the end of pitching the yeast and the end of the step of adding the wort to the fermentation vessel, the yeast may be contacted with oxygen for at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, for example from 2 to 5 hours. Contacting the yeast with oxygen may be achieved by aerating the wort in the fermentation vessel with oxygen or air, or it may be achieved by adding the wort in one or more wort portions, wherein one or more of the wort portions comprises dissolved oxygen. At higher oxygen concentrations, it may take longer for the oxygen in the wort to be depleted by the yeast, thus increasing the contact time between the yeast and oxygen. Different wort portions may have different dissolved oxygen concentrations in order to vary the contact time at different stages of adding the wort to the fermentation vessel. The wort portions comprising dissolved oxygen may have a dissolved oxygen concentration of from 1 mg / L to 35 mg / L, preferably from 1 to 25 mg / L, more preferably from 1 to 10 mg / L, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mg / L. In an embodiment, all of the wort portions comprise dissolved oxygen in the amounts recited above. The addition of the one or more wort portions to the fermentation vessel may take at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours and thereby contacting the yeast with oxygen for at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, for example from 2 to 5 hours. Adding a portion of the wort to the fermentation vessel may take from 15 to 90 minutes, preferably from 30 to 75 minutes, for example 30, 35, 40, 45, 50, 55, 60, 65, 70 or 75 minutes. There may be a rest time between adding wort portions, which may be from 50 to 150 minutes, for example, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 minutes. Alternatively, the wort portions may be added consecutively, i.e. without a rest period between additions. At least one wort portion comprising oxygen in the amounts recited above is added to the fermentation vessel after pitching the yeast and this may occur immediately after pitching the yeast. For example, 1, 2, 3, 4, 5, or 6 wort portions may be added to the fermentation vessel immediately after pitching the yeast. The yeast may be pitched at the beginning of, or immediately before, the addition of a wort portion. A time between pitching the yeast and the end of the addition of the wort comprising dissolved oxygen, or the final wort portion comprising dissolved oxygen, may be at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, for example from 2 to 5 hours, thereby contacting the yeast with oxygen for at least 2 hours. In embodiments where the wort is added in more than one portion, the cumulative time for adding the wort portions, that is, the sum for all wort portions of the time from the beginning of adding a wort portion to the end of adding that portion, may be at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, , for example from 2 to 5 hours, thereby contacting the yeast with oxygen for at least 2 hours. In some embodiments, the dissolved oxygen concentration of the wort does not fall below 0.1 mg / L before the final wort portion comprising dissolved oxygen is added to the fermentation vessel. It is preferred that the wort is not aerated / oxygenated after the step of adding the wort to the fermentation vessel is complete. In a particular embodiment, the wort is added as one portion comprising dissolved oxygen. In this embodiment, a wort comprising dissolved oxygen in an amount of from 1 to 25 mg / L, preferably from 1 to 10 mg / L, is added to the fermentation vessel, and wherein a time between pitching the yeast and the end of the addition of the wort may be at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, , for example from 2 to 5 hours, thereby contacting the yeast with oxygen for at least 2 hours. In a particular embodiment, adding the wort to a fermentation vessel comprises adding the wort in one or more wort portions, preferably at least 3 wort portions, to the fermentation vessel, wherein all of the wort portions comprise oxygen in an amount of from 1 to 10 mg / L, preferably wherein the yeast is pitched immediately before the addition of a wort portion, preferably the antepenultimate wort portion, and wherein a time between pitching the yeast and the end of the addition of the final wort portion may be at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, for example from 2 to 5 hours, thereby contacting the yeast with oxygen for at least 2 hours. In a particular embodiment, adding the wort to a fermentation vessel comprises adding the wort to the fermentation vessel in 6 wort portions, wherein all of the wort portions comprise oxygen in an amount of 1 to 10 mg / L, wherein the yeast is pitched immediately before the addition of the third or fourth wort portion, and wherein a time between pitching the yeast and the end of the addition of the final wort portion may be at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 5 hours, for example from 2 to 5 hours, thereby contacting the yeast with oxygen or for at least 2 hours. Fermentation conditions The present inventors have found that it is beneficial to ferment high gravity wort at a first, lower temperature then, after a time, increasing the temperature to a second, higher temperature. As shown in Figures 1a and 1b, this may reduce the fermentation time compared to a fermentation process in which the temperature remains constant. This can be particularly beneficial for high gravity fermentation because the increased carbohydrate concentration can increase the fermentation time. The first, lower temperature, which may be known as the fermentation temperature, is at least 11°C, preferably up to 15°C, preferably from 11 to 14°C, for example 11, 12, 13, or 14°C. It may be necessary to maintain the wort at this temperature using a cooling system incorporated into the fermentation vessel, e.g. a cooling jacket, because the action of the yeast on the wort may increase the temperature of the wort. The second, higher temperature may be at least 2°C higher than the first temperature, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11 °C higher than the first temperature. The second temperature may be from 14 to 25°C, preferably from 15 to 20°C, for example 15, 16, 17, 18, 19, or 20°C. It may also be necessary to maintain the wort at this temperature using a cooling system incorporated into the fermentation vessel, e.g. a jacket. The temperature may be increased from the first temperature to the second temperature at a rate of from 0.05°C / hour to 1°C / hour, preferably from 0.1 to 0.5°C / hour, for example 0.1, 0.2, 0.3, 0.4, or 0.5°C / hour. In a particular embodiment, the first temperature may be from 12-13°C and the second temperature may be from 18-19°C. The present inventors have discovered that the timing of the temperature increase from the first temperature to the second temperature is important. In the present invention, the temperature increase begins when one or more of the following conditions is reached: (i) a peak yeast cell count; (ii) a minimum FAN concentration; (iii) a minimum pH; (iv) an apparent extract of at least 5°P; and, (v) a residual fermentable sugar concentration of at least 4 °P Figure 1d shows the change in yeast cell count, FAN concentration and pH during the fermentation process. It may be beneficial for fermenting at high gravity for the temperature increase from the first temperature to the second temperature to begin when a peak yeast cell count is reached. This may allow for maximum fermentation efficiency. A peak yeast cell count may be reached at a maximum yeast cell count. Alternatively, a peak yeast cell count may be reached when, after a maximum yeast cell count, the yeast cell count is within 30%, preferably within 20%, preferably within 10%, of the maximum yeast cell count. The maximum yeast cell count is the highest yeast cell count reached during the fermentation phase. In absolute terms, a peak yeast cell count may be at least 30 million cells / mL, preferably from 30 to 70 million cells / mL, more preferably from 40 to 60 million cells / mL. Amino acids are taken up and metabolised by yeast during the yeast growth phase and it may be beneficial for the temperature increase to begin when a minimum FAN concentration is achieved. A minimum FAN concentration may be reached at a time when a FAN concentration does not decrease thereafter or does not substantially decrease thereafter. A minimum FAN concentration may be reached when a FAN concentration of the wort decreases by less than 20%, preferably less than 10%, over a period of up to 24 hours; or over a period of up to 12 hours; or over a period of up to 6 hours, for example 1,2,3, 4, 5, or 6 hours; or over a period of up to 2 hours. Apparent extract is a common parameter measured to follow the progress of fermentation. Apparent extract reduces from the original gravity during fermentation to a minimum towards the end of fermentation. Accordingly, the reduction in FAN concentration can be expressed per degree Plato reduction in apparent extract. A minimum FAN concentration may be reached when a FAN concentration increases or decreases by less than 25 ppm / °P reduction in apparent extract, preferably less than 10 ppm / °P reduction in apparent extract, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 ppm / °P reduction in apparent extract. In absolute terms, the minimum FAN concentration may be reached when less than 180 ppm, or from 50 to 150 ppm, for example 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 ppm. As with FAN concentration, pH usually stops decreasing, i.e. reaches a minimum, during fermentation and it may be beneficial for the temperature increase to being when a minimum pH is achieved. A minimum pH may be reached at a time when the pH of the wort does not decrease thereafter or does not substantially decrease thereafter. A minimum pH may be reached when a pH of the wort decreases by less than 0.5, more preferably less than 0.2, over a period of up to 24 hours; or over a period of up to 12 hours; or over a period of up to 6 hours, for example 1,2,3, 4, 5, or 6 hours; or over a period of up to 2 hours. In absolute terms, the minimum pH may be less than 4.7, preferably from 4 to 4.4 When expressed per degree Plato reduction in apparent extract, a minimum pH may be reached when a pH of the wort increases of decreases by less than 0.5 / °P reduction in apparent extract, preferably less than 0.2 / °P reduction in apparent extract, more preferably less than 0.1 / °P reduction in apparent extract. The temperature increase may begin when a particular apparent extract level is achieved, which may be from 5 to 20°P, preferably from 8 to 15°P, for example 8, 9, 10, 11, 12, 13, 14, or 15°P. A minimum residual fermentable sugar concentration may be required in order for the temperature increase to take place. This is because the temperature increase is caused by thermal energy produced by the action of yeast on the fermentable sugars in the wort. If the residual fermentable sugar concentration is too low, the temperature increase may not occur because the yeast does not have sufficient food to fuel the increase. Accordingly, the temperature increase may begin from the first to the second temperature when the residual fermentable sugar concentration is at least 4°P, preferably from 5 to 15°P, for example 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15°P. The temperature increase from the first temperature to the second temperature may begin when a peak yeast cell count; and / or a minimum FAN concentration; and / or a minimum pH; and / or an apparent extract of at least 5°P; and / or a residual fermentable sugar concentration of at least 4 °P is reached. The temperature increase from the first temperature to the second temperature may begin within 24 hours, preferably within 12 hours, more preferably within 6 hours, for example 1, 2, 3, 4, 5, or 6 hours, of the one or more conditions being reached. The temperature increase from the first temperature to the second temperature may begin from 36 to 96 hours after the step of adding the wort to the fermentation vessel is complete, for example 36, 42, 48, 54, 60, 66, 72, 78, 84, 90, or 96 hours after the step of adding the wort to the fermentation vessel is complete. Thus, the fermentation phase may last for from 36 to 96 hours. The process may further comprise a step of monitoring one or more parameters selected from the group consisting of a yeast cell count, a free amino nitrogen (FAN) concentration, a pH during fermentation, an apparent extract, and a residual fermentable sugar concentration. Once the temperature has been increased to the second temperature, the wort is maintained at the second temperature for a maturation phase. The end of maturation may be signified by the reaching of a total diacetyl concentration of less than 65 ppb, preferably less than 30 ppb is reached, and / or an acetaldehyde concentration of below 10 ppm, preferably below 5 ppm. The method of the present invention may allow the yeast to be harvested and reused at least 5 times, preferably from 5 to 20 times, more preferably from 7 to 12 times. Accordingly, the process may further comprise a step of harvesting yeast cells for use in further iterations of the process. Once the maturation phase is complete, the fermented / matured wort may be cooled. The step of cooling the fermented / matured wort to less than 4°C may take less than 100 hours, preferably from 60 to 80 hours, for example 60, 65, 70, 75, or 80 hours, most preferably from 12 to 48 hours, for example 12, 18, 24, 30, 36, 42 or 48 hours.. The method of the present invention may further comprise processing the fermented wort to provide a fermented beverage, preferably wherein the fermented beverage is a beer. The processing may include one or more of cold ageing, filtering and packaging the fermented beverage. The fermented beverage may be packaged in, for example, bottles, cans, kegs, casks or barrels. The present invention is additionally directed to a fermented beverage prepared by the method described hereinabove. Method variation As discussed hereinabove, in a variation of the method, the gravity of the wort provided in step a) may be increased during or after step b) by the addition of a solution comprising one or more fermentable sugars to the wort. In other words, adding the solution to the wort may increase the gravity of the wort. By adding the solution after step b) the yeast may grow in a lower gravity (and therefore less stressful) environment, which may mean that the yeast can be reused a greater number of times without impacting negatively on the sensorial profile and physico-chemistry aspects of the fermented beverage. The solution added in the variation differs from a wort in that it is not prepared by mashing grains and does not comprise, for example, amino acids or protein. Accordingly, the solution may consist of or consist essentially of the one or more fermentable sugars and water. The one or more fermentable sugars may be selected from the group consisting of glucose, sucrose, maltose, and maltotriose, preferably wherein the solution comprises glucose. Most preferably, the solution is a syrup, preferably a glucose syrup. The solution may comprise the one or more fermentable sugars at very high concentration. Preferably the solution has a gravity of from 20 to 90°P, preferably from 30 to 80°P, for example 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80°P. The solution comprising one or more fermentable sugars may be added to the wort during the step of adding the wort to the fermentation vessel. Alternatively, the solution is added to the wort after the step of adding the wort to the fermentation vessel. Accordingly, the solution may be added during the fermentation phase. The solution may be added when the apparent extract level of the wort reaches from 16 to 1°P, preferably from 12 to 1°P, more preferably from 8 to 1°P. Preferably, the solution comprising one or more fermentable sugars is added from 12 to 144 hours after the step of adding the wort to the fermentation vessel is complete, preferably from 24 to 120 hours after the step of adding is complete, more preferably from 36 to 108 hours after the step of adding the wort to the fermentation vessel is complete. The present inventors have surprisingly found that adding the solution at this stage has a beneficial impact on the attenuation, i.e. the conversion of sugars to alcohol, in that it may increase the attenuation compared to adding the solution at a different time (see Figure 5a). In a particular embodiment, the solution comprises glucose at a gravity of from 20 to 80°P and is added from 36 to 108 hours after the step of adding the wort to the fermentation vessel is complete. In a particular embodiment, the present invention provides a method of fermenting a high gravity wort comprising: (a) providing a wort comprising zinc in an amount of from 150 to 250 ppb, an ammonium salt in an amount of from 1 to 2 ppm nitrogen / °P, and comprising oxygen in an amount of from 1 to 25 mg / L, wherein the wort has a free amino nitrogen content of from 10 to 16 ppm / °P; (b) adding the wort to a fermentation vessel at a temperature of from 8 to 11°C and, during the step of adding, pitching a yeast into the wort at a pitching rate of from 1.2 to 2 million cells / mL / °P; and wherein a time between pitching the yeast and the end of the addition of the wort may be from 2 to 15 hours, , for example from 2 to 5 hours, thereby contacting the yeast with oxygen for at least 2 hours; (c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase; (d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached: (i) a peak yeast cell count; (ii) a minimum FAN concentration; (iii) a minimum pH; (iv) an apparent extract of at least 5°P; and, (v) a residual fermentable sugar concentration of at least 4 °P; (e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and, (f) cooling the wort to less than 4°C to provide a fermented wort. In a particular embodiment, the present invention provides a method of fermenting a high gravity wort comprising: (a) providing a wort comprising zinc in an amount of from 150 to 250 ppb, an ammonium salt in an amount of from 1 to 2 ppm nitrogen / °P, and comprising oxygen in an amount of from 1 to 25 mg / L, wherein the wort has a free amino nitrogen content of from 10 to 16 ppm / °P; (b) adding the wort to a fermentation vessel at a temperature of from 8 to 11°C and, during the step of adding, pitching a yeast into the wort at a pitching rate of from 1.2 to 2 million cells / mL / °P; and wherein a time between pitching the yeast and the end of the addition of the wort may be from 2 to 15 hours, , for example from 2 to 5 hours, thereby contacting the yeast with oxygen or for at least 2 hours; (c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase; (d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached: (i) a peak yeast cell count, wherein a peak yeast cell count is reached at a maximum yeast cell count; or when, after a maximum yeast cell count, the yeast cell count is within 30%, preferably within 20%, of the maximum yeast cell count; (ii) a minimum FAN concentration, wherein a minimum FAN concentration is reached when a FAN concentration of the wort does not decrease thereafter or does not substantially decrease thereafter; or a FAN concentration of the wort decreases by less than 20%, preferably less than 10%, over a period of up to 12 hours; or, when a FAN concentration is from 50 to 150 ppm; (iii) a minimum pH, wherein a minimum pH is reached when a pH of the wort does not decrease thereafter or does not substantially decrease thereafter; or when a pH of the wort decreases by less than 0.5, over a period of up to 12 hours; or, when a pH of the wort is less than 4.7, preferably from 4 to 4.4; (iv) an apparent extract of from 7.5 to 12.5°P; and, (v) a residual fermentable sugar concentration of from 5 to 15°P; (e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and, (f) cooling the wort to less than 4°C to provide a fermented wort. In a particular embodiment, the present invention provides a method of fermenting a high gravity wort comprising: (a) providing a wort comprising zinc in an amount of from 150 to 250 ppb, an ammonium salt in an amount of from 1 to 2 ppm nitrogen / °P, and comprising oxygen in an amount of from 1 to 25 mg / L, wherein the wort has a free amino nitrogen content of from 10 to 16 ppm / °P; (b) adding the wort to the fermentation vessel in 6 wort portions at a temperature of from 8 to 11°C, wherein all of the wort portions comprise oxygen in an amount of from 1 to 25 mg / L, pitching a yeast into the wort at a pitching rate of from 1.2 to 2 million cells / mL / °P, wherein the yeast is pitched immediately before the addition of the third or fourth wort portion, and wherein a time between pitching the yeast and the end of the addition of the final wort portion may be at least 2 hours, preferably from 2 to 15 hours, for example from 2 to 5 hours, thereby contacting the yeast with oxygen or for at least 2 hours; (c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase; (d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature is increased when one or more of the following conditions is reached: (i) a peak yeast cell count; (ii) a minimum FAN concentration; (iii) a minimum pH; (iv) an apparent extract of at least 5°P; and, (v) a residual fermentable sugar concentration of at least 4 °P; (e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and, (f) cooling the wort to less than 4°C to provide a fermented wort. The present invention may additionally be described by the following non-limiting examples. EXAMPLES Methods of measurement Yeast cell count Principle: A haemocytometer is based on a microscope slide. It is marked with a grid. The grid squares are a known size. By knowing the size of the grid, and the volume of liquid enclosed within the grid, a count of yeast cells present can be multiplied up to give a count per ml of sample. Procedure: Ensure the yeast in suspension is uniform by shaking of the sample. If necessary, dilute the suspension so that there are approximately 5 yeast cells per small square. Place the coverslip on the haemocytometer slide. Use a Pasteur pipette to transfer one drop of yeast suspension to the open edge of the counting chamber, by capillary action. Examine under the microscope and count at least 200 cells, and the number of squares in which they were found. Make a note of the size of the squares counted, as this will affect the calculation of results. Results are expressed as cells per ml. Calculate the number of yeast cells thus: Each medium square (A) has a volume of 0.000004 ml. Calculate the Average number of cells per square. Multiply the average by 2.5 X 105 = cells per ml. The Thoma counting chamber described here is a haemocytometer having 16 large squares (A), each divided into 16 small squares (B). Free amino nitrogen content Principle: The diluted sample is heated in the presence of ninhydrin at pH 6.7 and the colour which develops is measured at 570 nm by comparison with the glycine standard solution. The method must be performed in duplicate and the result is reported as the average of the 2 measurements. Sample preparation: Filter the sample over a filter paper and decarbonate (beer) if necessary. Dilute the samples. Recommended dilution factor: beer 50 and wort 100. Procedure: Pipette 2 ml diluted sample in a test tube and add 1 ml colour reagent. Mix on a vortex mixer. Heat the tube for exactly 16 min in a boiling water bath. Cool the tube in a water bath at 20° C for 20 min. Add 5 ml diluting solution, mix and put the tube back into the water bath at 20° C for 30 min. Measure the absorbance at 570 nm in a 10 mm cell against a reagent blank prepared from the reagents (1 ml colour reagent and 5 ml diluting solution) plus 2 ml distilled water in place of the sample. References: American Society of Brewing Chemists, Report of Sub-Committee on Free Amino Nitrogen. Proceedings 1974, 32, 34; Proceedings 1975, 33, 88. / Lie, S., Journal of the Institute of Brewing. 1973, 79, 37.1 Satake, K., Okryama, T., Ohashi, M. and Shinoda, T., Journal of Bio-chemistry. Japan, 1960, 47 (5), 654.1 Wylie, E.B. and Johnson, N.J., Bioch Apparent extract The apparent extract was measured by the European Brewing Council method 9.4 (Original, Real and Apparent Extract and Original Gravity of Beer). Residual fermentable sugars The residual fermentable sugar concentration was measured by subtracting the limit attenuation (measured according to the European Brewing Council method 8.6.1) from the apparent extract. Total diacetyl content American Society of Brewing Chemists Method Beer 25B. Spectrophotometric Determination of Total VDK by Distillation and a-Naphthol Creatine Reaction Dissolved oxygen content European Brewing Convention Method Beer 9.37.2 - Measurement of Dissolved Oxygen by Electrochemical Sensors. Acetaldehyde content Samples of beer (5 mL) were degassed by sonication or filtration and placed in a headspace vial with a PTFE septum which was analysed by gas chromatography using a PerkinElmer Clarus 690 GC with a TurboMatrix HS-40. Example 1 - Fermentation at an original gravity of 18.3°P A cylindro-conical fermentation vessel was filled with portions of a wort (1150 hL) having an original gravity of 18.3°P and containing zinc in an amount of 600g zinc sulfate.7H2O (198 ppb) at a temperature of 10.5°C to a total volume of 6900 hL according to the filling regime in Table 1 below. The portions comprising oxygen were aerated with air in-line when transferring to the fermentation vessel to a dissolved oxygen content of 8 mg / L. The free amino nitrogen (FAN) content of the wort was 230 ppm at 18.3 °P. The yeast was pitched at the start of filling the third portion at a rate of 27 million cells / mL. Table 1 Wort portion Pitching rate Air injection rate (g / hL) Filling time (mins) Wait time between portions (mins) 1 17 50 115 2 17 53 85 3 100% 17 48 89 4 17 52 98 5 17 52 74 6 17 51 After filling, the wort was treated according to Figures 2a and 2b. The temperature was raised over an approximately 12 hour period to a fermentation temperature of 12°C and held at this temperature for approximately 36 hours. At this time, i.e. approximately 48 hours after filling completed, a peak yeast cell count was reached and the apparent extract was approximately 11°P. The FAN level was 76 ppm and the pH was 4.14. The temperature was increased to 18°C. The wort was held at this temperature for approximately 100 hours, at which point fermentation was complete and the wort was rapidly cooled to below 4°C over approximately 12 hours. The apparent extract at the end of fermentation was approximately 4°P. Figure 2c shows the concentration of total butanedione, total pentanedione and acetaldehyde during the fermentation. Example 2 - Fermentation at an original gravity of 20.8°P A cylindro-conical fermentation vessel was filled with portions of a wort (1150 hL) having an original gravity of 20.8°P, zinc in an amount of 600g zinc sulfate.7H2O (198 ppb) and an ammonium sulfate content of 18 g / hL (38 ppm nitrogen at 20.8°P) at a temperature of 10.5°C to a total volume of 6900 hL according to the filling regime in Table 2 below. The portions comprising oxygen were aerated with air in-line when transferring to the fermentation vessel to a dissolved oxygen concentration of 8 mg / L. The free amino nitrogen (FAN) content of the wort was 278 ppm at 20.8°P. The yeast was pitched at the start of filling the third portion at a rate of 31.5 million cells / mL. Table 2 Wort portion Pitching rate Air injection rate (g / hL) Filling time (mins) Wait time between portions (mins) 1 22 48 67 2 22 47 124 3 100% 22 47 124 4 22 46 83 5 22 55 81 6 22 46 After filling, the wort was treated according to Figure 3. The temperature was raised over a 24 hour period to a fermentation temperature of 13°C and held at this temperature for approximately 42 hours. At this time, i.e. approximately 66 hours after filling completed, a peak yeast cell count was reached and the apparent extract was approximately 12°P. The FAN level was 74 ppm and the pH was 4.19. The temperature was increased to 19°C. The wort was held at this temperature for approximately 84 hours, at which point fermentation was complete and the wort was rapidly cooled to below 4°C over approximately 12 hours. The apparent extract at the end offermentation was approximately 5°P. Example 3 - Fermentation at an original gravity of 21 °P A cylindro-conical fermentation vessel was filled with portions of a wort (1150 hL) having an original gravity of 21°P, zinc in an amount of 600g zinc sulfate.7H2O (198 ppb) and an ammonium sulfate content of 18 g / hL (38 ppm nitrogen at 21 °P) at a temperature of 10.5°C to a total volume of 6900 hL according to the filling regime in Table 4 below. The portions comprising oxygen were aerated with air in-line when transferring to the fermentation vessel to a dissolved oxygen concentration of 8 mg / L. The free amino nitrogen (FAN) content of the wort was 250 ppm at 21 °P. The yeast was pitched at the start of filling the third portion at a rate of 31.5 million cells / mL. Table 4 Wort portion Pitching rate Air injection rate (g / hL) Filling time (mins) Wait time between portions (mins) 1 22 47 120 2 22 48 121 3 100% 22 47 121 4 22 47 122 5 22 47 120 6 22 47 After filling, the wort was treated according to Figure 4a. The temperature was raised over a 24 hour period to a fermentation temperature of 13°C and held at this temperature for approximately 36 hours. At this time, i.e. approximately 60 hours after filling completed, a peak yeast cell count was reached and the apparent extract was approximately 12.5°P. The FAN level was 63 ppm and the pH was 4.39. The temperature was increased to 19°C. The wort was held at this temperature for approximately 86 hours, at which point fermentation was complete and the wort was rapidly cooled. The apparent extract at the end of fermentation was approximately 4.5°P. The fermented worts of Examples 1-3 were processed to provide a fermented beverage (beer) according to processes known in the art and analysed to provide the data in Table 5 below. Table 5 Target range Example 1 Example 2 Example 3 Alcohol (v / v) 4.6-5.10% 4.99 4.99 4.92 Real Extract 2.80-4.00 °P 3.96 3.98 4.03 Apparent Extract 2.07-2.60 °P 2.15 2.17 2.24 Original gravity °P 11.56 11.59 11.53 Real degree of fermentation (RDF) % 67.1 67.03 66.4 Apparent degree of fermentation (ADF) % 81.4 81.3 80.8 Residual fermentable sugar 0.35 (in range) 0.53 (in range) 0.39 (in range) pH 4.32 4.29 4.31 SO2 4-10 ppm 5.1 5.4 4.9 Acetaldehyde Max 7 ppm 3.50 3.61 5.09 Ethyl Acetate 5.80 10.85 10.16 Free diacetyl Max 25 ppb 14.1 11.2 9.44 The process of the invention allows fermentation to be performed at high gravity, including at least 20°P, while maintaining a desirable composition and flavour profile.

Claims

1. A method of fermenting a high gravity wort comprising:(a) providing a wort comprising zinc in an amount of at least 100 ppb and, optionally, an ammonium salt in an amount of at least 1 ppm nitrogen / °P, wherein the wort has a free amino nitrogen content of at least 10 ppm FAN / °P;(b) adding the wort to a fermentation vessel at a temperature below 11 °C and, during the step of adding, pitching a yeast into the wort and contacting the yeast with oxygen for at least 2 hours;(c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase;(d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached:(i) a peak yeast cell count;(ii) a minimum FAN concentration;(iii) a minimum pH;(iv) an apparent extract of at least 5°P; and,(v) a residual fermentable sugar concentration of at least 4 °P;(e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and,(f) cooling the wort to less than 4°C to provide a fermented wort.

2. The method of fermenting a high gravity wort according to claim 1, wherein the wort is provided with a gravity of at least 18°P, preferably from 18 to 30°P, more preferably from 18 to 25°P.

3. The method of fermenting a high gravity wort according to claim 1 or claim 2, wherein the wort comprises zinc in an amount of from 100 to 2000 ppb, preferably from 100 to 500 ppb, more preferably from 150 to 250 ppb.

4. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort comprises an ammonium salt, preferably one ormore selected from the group consisting of ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium phosphate.

5. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort comprises an ammonium salt in an amount of from 0.1 to 5 ppm nitrogen / °P, preferably from 0.5 to 3 ppm nitrogen / °P, more preferably from 1 to 2 ppm nitrogen / °P; or, wherein the wort comprises an ammonium salt in an amount of at least 5 g / hL, preferably from 10 to 30 g / hL.

6. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort is provided with a dissolved oxygen concentration of from 1 to 35 mg / L, preferably from 1 to 25 mg / L, more preferably from 1 to 10 mg / L.

7. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort is provided with a FAN concentration of from 10 to 16 ppm / °P.

8. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort is added to the fermentation vessel at a temperature of from 6 to 11 °C, preferably from 8 to 11 °C.

9. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the yeast is pitched at a rate of at least 1 million cells / mL / °P, preferably from 1.2 to 2 million cells / mL / °P.

10. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the yeast is pitched when at least 30% of the wort; or at least 50% of the wort; or at least 70% of the wort has been added to the fermentation vessel.

11. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the first temperature is up to 15°C, preferably from 11 to 14°C.

12. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the second temperature is at least 2°C higher than the first temperature, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11 °C higher than the first temperature.

13. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the second temperature is from 14 to 25°C, preferably from 15 to 20°C.

14. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein a peak cell count is reached at a maximum yeast cell count; or wherein a peak yeast cell count is reached when, after a maximum yeast cell count, the yeast cell count is within 30%, preferably within 20%, of the maximum yeast cell count.

15. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein a minimum FAN concentration is reached:when a FAN concentration does not decrease thereafter or does not substantially decrease thereafter; or,when a FAN concentration of the wort decreases by less than 20%, preferably less than 10%, over a 24 hour period; or a 12 hour period; or a 6 hour period; or a 2 hour period; or,when the minimum FAN concentration is less than 180 ppm; or from 50 to 150 ppm.

16. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein a minimum pH is reached:when a wort pH does not decrease thereafter or does not substantially decrease thereafter; or,when a pH of the wort decreases by less than 0.5, more preferably less than 0.2, over a 24 hour period; or a 12 hour period; or a 6 hour period; or a 2 hour period; or,when a pH of the wort is less than 4.7, preferably from 4 to 4.4.

17. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the temperature increase begins when the apparent extract is from 5 to 20°P, preferably from 8 to 15°P.

18. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the temperature increase begins when the residual fermentable sugar concentration is from 5 to 15°P.

19. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the temperature increase begins within 24 hours, preferably within 12 hours, more preferably within 6 hours of the one or more conditions being reached.

20. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the yeast is contacted with oxygen for from 2 to 15 hours, more preferably from 2 to 10 hours.

21. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the wort is added to the fermentation vessel in one or more wort portions, wherein one or more of the wort portions comprises dissolved oxygen, preferably wherein all the wort portions comprise dissolved oxygen.

22. The method of fermenting a high gravity wort according to claim 21, wherein the wort portions comprising dissolved oxygen have a dissolved oxygen concentration of from 1 mg / L to 35 mg / L, preferably from 1 to 25 mg / L, more preferably from 1 to 10 mg / L.

23. The method of fermenting a high gravity wort according to claim 21 or 22, wherein at least one wort portion comprising dissolved oxygen is added to the fermentation vessel after pitching the yeast.

24. The method of fermenting a high gravity wort according to claim 23, wherein a time between the end of pitching the yeast and the end of the addition of the final wort portion comprising dissolved oxygen is at least 2 hours, preferably from 2 to 15 hours,more preferably from 2 to 10 hours, thereby contacting the yeast with oxygen for at least 2 hours.

25. The method of fermenting a high gravity wort according to any one of claims 1 to 21, wherein a wort comprising dissolved oxygen in an amount of from 1 to 25 mg / L, preferably from 1 to 10 mg / L, is added to the fermentation vessel, and wherein a time between the end of pitching the yeast and the end of the step of adding the wort is at least 2 hours, preferably from 2 to 15 hours, more preferably from 2 to 10 hours, thereby contacting the yeast with oxygen for at least 2 hours.

26. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein the yeast is reused in a further iteration of the process at least 5 times, preferably from 7 to 12 times.

27. The method of fermenting a high gravity wort according to any one of the preceding claims comprising:(a) providing a wort comprising zinc in an amount of from 100 to 500 ppb, an ammonium salt in an amount of from 1 to 2 ppm nitrogen / °P, and comprising dissolved oxygen in an amount of from 1 to 25 mg / L, wherein the wort has a free amino nitrogen content of from 10 to 16 ppm / °P;(b) adding the wort to a fermentation vessel at a temperature of from 8 to 11°C and, during the step of adding, pitching a yeast into the wort at a pitching rate of from 1.2 to 2 million cells / mL / °P; and wherein a time between pitching the yeast and the end of the addition of the wort is from 2 to 15 hours, thereby contacting the yeast with oxygen for at least 2 hours;(c) incubating the wort at a first temperature of at least 11 °C for a fermentation phase;(d) increasing the temperature of the wort to a second temperature which is higher than the first temperature, wherein the temperature increase begins when one or more of the following conditions is reached:(i) a peak yeast cell count;(ii) a minimum FAN concentration;(iii) a minimum pH;(iv) an apparent extract of at least 5°P; and,(v) a residual fermentable sugar concentration of at least 4 °P;(e) maintaining the wort at the second temperature for a maturation phase, preferably until a total diacetyl concentration of less than 65 ppb and / or an acetaldehyde concentration of below 10 ppm is reached; and,(f) cooling the wort to less than 4°C to provide a fermented wort.

28. The method of fermenting a high gravity wort according to any one of the preceding claims, wherein a solution comprising one or more fermentable sugars is added to the wort, preferably wherein the one or more fermentable sugars is selected from the group consisting of glucose, sucrose, maltose, and maltotriose, even more preferably glucose, most preferably wherein the solution is a glucose syrup.

29. The method of fermenting a high gravity wort according to claim 28, wherein the solution has a gravity of from 60 to 90°P, preferably from 70 to 80°P.

30. The method of fermenting a high gravity wort according to claim 28 or claim 29, wherein the solution is added to the wort during the step of adding the wort to the fermentation vessel; or, wherein the solution is added to the wort after the step of adding the wort to the fermentation vessel.

31. The method of fermenting a high gravity wort according to any one of claims 28 to 30, wherein the solution is added to the wort during the fermentation phase.

32. The method of fermenting a high gravity wort according to any one of claims 28 to 31, wherein the solution is added from 12 to 144 hours after the step of adding is complete, preferably from 24 to 120 hours after the step of adding is complete, more preferably from 36 to 108 hours after the step of adding is complete.

33. The method of fermenting a high gravity wort according to any one of claims 28 to 32, wherein the process further comprises a step of processing the fermented wort to provide a fermented beverage, preferably wherein the fermented beverage is a beer.

34. A fermented beverage prepared by the process according to any one of claims 1 to 33.

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