MONITORING AND CONTROL OF YEAST PROPAGATION

Description

[0001] The present invention relates to a method, in particular a computer-implemented method, for controlling and / or monitoring yeast propagation, for example in a large-scale industrial plant. In particular, the invention relates to yeast propagation in a brewery.

[0002] The production of beer comprises several complex process steps, such as malting grain, mashing, lautering, wort boiling, and fermentation. Reliable monitoring, control, and optimization of such complex processes require simultaneous knowledge of a wide variety of process parameters and their underlying relationships. For example, German patent DE 10 2019 110 821 A1 discloses a method for determining and / or monitoring the concentration of maltodextrin and / or maltose based on density and the speed of sound in a mashing process. This allows for the precise determination of the time required for saccharification of the mash.

[0003] Wort fermentation involves the preparation or inoculation of hopped wort with yeast. Yeast propagation typically occurs in batches, where a fresh yeast culture is introduced into the wort in each batch and used entirely for the subsequent fermentation. Yeast propagation, in this context, refers to the increase in the biomass and cell count of the respective yeast population, which occurs through several distinct growth phases. Ideally, the result should be a yeast strain with the highest possible vitality (i.e., high fermentation strength) and viability (i.e., high lifespan). To ensure this, various measurements, with or without sampling, can be taken during the fermentation process to monitor the yeast propagation.However, a uniform or standardized procedure for monitoring and / or controlling yeast propagation is not available. Such a procedure is also difficult to implement for such a multivariate biological system with complex growth behavior.

[0004] EP 2 846 160 A1 describes beer fermentation using fuzzy logic to calculate models that describe the behavior of the mash as a function of measured parameters such as temperature. A measuring unit is provided for measuring a parameter (e.g., alcohol or CO2 content) that correlates with the extract value. Extrapolation is performed from the extract values ​​to determine optimal measurement points and minimize the number of measurements required. Fermentation is then terminated by cooling if the change in the extract value is too small and a measured VDK value falls below a target value.

[0005] US 2008 / 0109100 A1 discusses computational models for monitoring fermentation.

[0006] The invention is based on the objective of improving the control and / or monitoring of yeast propagation.

[0007] This problem is solved by a method, in particular a computer-implemented method, for controlling and / or monitoring yeast propagation, comprising the method steps of the first claim.

[0008] The original gravity, measured in degrees Plato (°P), refers to the concentration of dissolved substances from malt and hops in the wort before fermentation begins and at the start of yeast propagation. During yeast propagation, this value decreases due to yeast metabolism. The concentration of dissolved substances from malt and hops after yeast propagation is complete is called the residual extract.

[0009] By considering a logistic propagation model, it is possible to accurately predict the duration of the yeast propagation process. The invention is based on the understanding that, of the many possible influencing factors for yeast propagation, the original gravity and temperature at the start time are crucial. Monitoring and / or controlling yeast propagation is thus easily achievable; in particular, the duration of yeast propagation can be optimized by predicting the end time.

[0010] One aspect of the process involves determining the free amino nitrogen (FAN) content of the wort and using it to calculate the theoretical end time based on the propagation model. The FAN content is particularly important for yeast metabolic activity, yeast growth, and the yeast's physiological state. The FAN content can be determined regularly, for example, by taking samples during process controls in the brewery.

[0011] Another embodiment of the method involves determining or measuring the temperature of the mixture during yeast propagation. Temperature is a dominant factor influencing the growth rate of yeast cells and thus significantly impacts the speed of yeast propagation. For example, detecting a temperature change allows for appropriate adjustments to the prediction of the end time of yeast propagation.

[0012] According to the invention, an actual value for the extract content of the mixture is determined or measured during yeast propagation. The extract content can be used, for example, to monitor the nutrient supply to the yeast during the yeast propagation process.

[0013] Furthermore, it is advantageous to determine or measure the alcohol content, particularly the ethanol content, of the mixture during yeast propagation. During yeast propagation, extracellular ethanol accumulates, which also influences the yeast's growth rate.

[0014] In one embodiment of the invention, the dissolved oxygen content of the mixture is determined or measured during yeast propagation. This value, in turn, can be used to verify and / or monitor whether the wort has reached saturation.

[0015] One embodiment of the process involves using a model for extract content in the mixture as a propagation model, whereby the extract content is determined based on the original gravity at the start time, a target value for the residual extract content and taking into account a substrate uptake rate, a temperature rate and a duration for a lag phase during yeast propagation.

[0016] Specifying a target value for the residual extract content serves to ensure an adequate supply of nutrients and vitality for the yeast until the end of yeast propagation.

[0017] The substrate uptake rate allows the specific growth kinetics of yeast propagation to be incorporated into the propagation model. For yeast propagation, all substrates are supplied to the yeast at the beginning of the process. Thus, the yeast cells grow until the substrates are exhausted.

[0018] The temperature rate also significantly influences the speed of yeast reproduction and is therefore included in the determination of the growth rate within the propagation model.

[0019] The lag phase refers to a delay at the beginning of yeast propagation, which occurs particularly when yeast culture is over-inoculated into the wort. During this phase, the yeast cells are biochemically active, but they do not divide. Therefore, including the duration of the lag phase is also advantageous for accurately predicting the end time of yeast propagation.

[0020] According to the invention, a reference value for the extract content is determined using the propagation model. The reference value can be determined, for example, continuously or at predetermined times during yeast propagation.

[0021] According to the invention, the actual value for the extract content is compared with the reference value for the extract content. If a deviation between the actual value and the reference value exceeds a predefinable limit, at least one influencing factor for yeast propagation is varied depending on the deviation. Ideally, the time of determination of the actual value is taken into account when determining the reference value for the extract content, or both values ​​are determined for the same time. The comparison thus enables continuous monitoring and / or control of the process.

[0022] In one embodiment of the invention, the supply of oxygen is suitably adjusted, in particular regulated or controlled, during yeast propagation. In another embodiment of the invention, the end time for yeast propagation, predicted based on the propagation model, is adapted or changed according to the respective conditions.

[0023] For example, it is conceivable to adjust the temperature of the mixture during yeast propagation based on the deviation between the actual value and the reference value of the extract content, and in particular to regulate or control it in this way.

[0024] One design also includes the aeration of the mixture during yeast propagation, which is adjusted, in particular regulated or controlled, based on the deviation between the actual value and the reference value of the extract content and the dissolved oxygen content.

[0025] One aspect of the process involves determining the initial concentration of yeast at the start time.

[0026] In this context, it is advantageous to determine a yeast biomass concentration based on the propagation model, the pitching concentration and a target value for the yeast concentration, which is related to the target value for the residual extract content.

[0027] In this context, it is also advantageous to determine a viable yeast cell concentration during propagation based on the biomass concentration. This allows for monitoring of the cell concentration without direct measurement.

[0028] A further refinement involves determining the pH value of the mixture. This, in turn, serves to monitor the microbiological safety of the process.

[0029] The various factors influencing yeast propagation, such as extract content, FAN content, temperature, alcohol or ethanol content, dissolved oxygen content, and pH value, can each be determined at specific, predefined intervals or continuously. Determining individual factors through sampling and subsequent analysis is possible, as is direct measurement during the process. For direct measurement, suitable sensors for determining the respective factor can be attached to or inside a container used for yeast propagation. These sensors can include thermometers, oxygen sensors, and / or pH sensors.For the determination of density and / or viscosity and with influencing factors dependent on these quantities, such as alcohol content, reference is made in this context, for example, to the devices and methods which are referred to in DE 10 2018 127 526 A1, DE 10 2016 120 326 A1, DE 10 2016 111 134 A1 or DE 10 2015 112 421 A1 or also DE 10 2014 119 061 A1.

[0030] Using the propagation model, it is possible to predict an ideal course for yeast propagation under given conditions with regard to the duration and the desired number of living cells, and to control it appropriately by determining at least one influencing factor in parallel.

[0031] The process can be carried out on a computing unit or computer at the location of the yeast propagation, for example, in the brewery. Alternatively, it can be performed using an external computing unit, provided that the necessary measurement data is transmitted to this unit. For example, the process can be implemented via a cloud application. In this case, the measuring devices for determining the values ​​of the aforementioned influencing factors, such as a thermometer or an oxygen sensor, are preferably equipped with means for transmitting measured values ​​to the cloud.

[0032] The invention and its advantageous embodiments are explained in more detail with reference to the following figures. They show: Fig. 1 : for example, a container for carrying out yeast propagation and Fig. 2: the residual extract and the biomass concentration, each in the form of measurement curves and reference curves calculated using the propagation model.

[0033] In the figures, identical elements are labelled with the same reference symbol.

[0034] In Fig. 1 Figure 1 is a schematic and exemplary illustration of a vessel 1 for yeast propagation in a brewery. The vessel 1 includes an inlet 2 for mixing the hopped wort W with yeast H. Advantageously, at the beginning of the yeast propagation process, the pitching concentration of the yeast H, the temperature T inside the vessel 1, and, if applicable, the FAN content of the yeast H are determined. Subsequently, the yeast propagation process begins for the mixture G.

[0035] Container 1 further includes an outlet 3 for extraction and a device 4 for venting the container 1. For monitoring and / or control, an oxygen sensor 5 and a thermometer 6 are also installed in the tank in the example shown here. A heating / cooling device [not shown] may also be present for adjusting the temperature T in container 1 during yeast propagation.

[0036] The present invention provides a means for monitoring and / or controlling yeast propagation. It enables a growth process under controlled conditions and the harvesting of the yeast at the right time, i.e., when the cell count and vitality of the yeast are as high as possible.

[0037] Numerous descriptions of various factors influencing yeast propagation, as well as models for describing the yeast propagation process, are already known from the prior art, such as in the dissertation "Mathematically Based Management of Saccharomyces sp. Batch Propagation and Fermentations" by T. Kurz (2002) at the Technical University of Munich, or in "Modeling of the Bacterial Growth Curve" by MH Zwietering et al. in Applied and Environmental Microbiology, pp. 1875-1881, 1990. However, since yeast propagation is a complex, multivariate problem, the available models utilize a multitude of variables and different influencing factors and are only partially suitable for the practical control and / or monitoring of yeast propagation. Furthermore, many of the influencing factors are difficult to obtain directly, especially continuously, during yeast propagation.The present invention thus relates to a simplification of known models and descriptions, which allows for targeted control and / or monitoring of yeast propagation. A key underlying principle of the invention relates to the targeted selection of essential influencing factors in the creation of the propagation model.

[0038] The starting point for modeling yeast propagation is a logistic propagation model, as described in (Speers, et al., 2003), which describes the extract decrease S as a function of time t, a substrate uptake rate µ s , an extract difference ΔS=S 1 -S 2 between the original gravity S 1 and a target value for the residual extract content S 2 and a duration for the lag phase λ: S t = S 2 − ΔS 1 + e μ s λ − t

[0039] The determination of the substrate uptake rate µx is based on the application of Monod kinetics to account for the dependence of the growth rate R on a limiting substrate concentration during the growth process due to nutrient depletion, accumulation of toxic metabolic products, and ion balance. As described in the article "Growth of Saccharomyces cerevisiae is controlled by its limited respiratory capacity: formulation and verification of a hypothesis" by B. Sonnenleitnert and O. Käppeli, published in Biotechnology and Bioengineering, Vol. XXVIII, pp. 927-937, John Wiley & Sons, Inc., 1986, the substrate uptake rate µx is given by: μ s = μ s max ⋅ min Z Z + K Z N N + K n ⋅ K E K E + E

[0040] Z describes the sugar concentration, N the nitrogen concentration, E the ethanol content, µ s,max the maximum specific growth rate, and K s the half-maximal concentration of the substrates.

[0041] The dependence on temperature T in the growth of microorganisms as the dominant influencing factor for the growth process is demonstrated using an extended form of the Belehrädek model for the temperature rate r, as described in "Model for Bacterial Culture Growth Rate Throughout the Entire Biokinetic Temperature Range" by DA Ratowsky et al., published in Journal of Bacteriology, p.1222-1226, 1983. r = a ∗ T − T min ∗ 1 − e b ∗ T − T max .

[0042] Here, Tmin and Tmax describe a minimum and maximum growth temperature, respectively, and a and b are empirical parameters. Based on this temperature rate, the duration of the lag phase λ as a function of the temperature T is: λ = a T − T min ⋅ 1 − e b ⋅ T − T max − 2 , as in "Modeling of Bacterial Growth with Shifts in Temperature" by MH Zwietering et al., Applied and Environmental Microbiology, p. 204-213, 1994, proposed.

[0043] This allows the extract content S to be determined as a function of time t using the following propagation model S(t): S t = S 2 − ΔS 1 + e − μ s max ⋅ min S S + K s N N + K n ⋅ a ⋅ T − T min ⋅ 1 − e b ⋅ T − T max 2 t − a ⋅ T − T min ⋅ 1 − e b ⋅ T − T max − 2 + c c represents another free parameter.

[0044] Using the propagation model S(t) according to the invention, it is possible to determine a theoretical end time t end for yeast propagation based on the original gravity E 1 , and the temperature T at a start time t start .

[0045] The extract decrease dS t dt is related to the increase in biomass dX t dt , thus related to the biomass concentration X(t) as a function of time t. The extract decrease dS t dt This corresponds to the nutrient uptake of the yeast, which is why the biomass concentration X increases proportionally with the decrease in extract S. The proportionality factor Y is called the biomass yield and represents the amount of biomass per substrate. The rate of biomass growth dX t dt or the biomass growth rate µ x is thus calculated from the substrate uptake rate µ s as follows: μ X = Y ⋅ μ S

[0046] It is therefore possible to calculate the increase in biomass ΔX from the extract difference ΔE. The biomass concentration X, or the yeast concentration, can be determined from the decrease in extract S without the need for any further direct measurement. In this way, cell concentration monitoring is also possible.

[0047] In Fig. 2The residual extract S and the biomass concentration X are each shown as a function of time t in the form of measured values ​​obtained in an experimental measurement (S m (t) and X m (t), respectively) and of reference curves calculated using the propagation model S(t) and X(t), respectively (dashed and solid lines). For the propagation model S(t), an extract difference ΔS = 4% was calculated in this context, while the measured extract difference ΔS was slightly larger. The model satisfactorily reflects the process of yeast propagation. Reference sign

[0048] 1 Vessel 2 Inlet 3 Outlet 4 Aeration device 5 W Oxygen sensor 6 Thermometer Wort H Yeast T Temperature FANFAN content G Mixture of wort and yeast S Extract decrease t Time ΔS Extract difference S1 Original gravity S2 Target value for residual extract content λ Duration of the lag phase µx Substrate uptake rate R Growth rate Z Sugar concentration N Nitrogen concentration E E Ethanol content µs,max Maximum specific growth rate Ks Half-maximum concentration of substrates Tmin Minimum growth temperature Tmax Maximum growth temperature a, empirical parameters S(t) Propagation model tstart Start time tend End time X(t) Biomass concentration Y Proportionality factor, biomass yield µx Biomass growth rate ΔX Increase in biomass Sm(t) Measured values ​​for extract content Xm(t) Measured values ​​for biomass concentration

Claims

1. A method, in particular a computer-implemented method, for controlling and / or monitoring yeast propagation, comprising the following process steps: - Providing a mixture (G) of yeast cells (H) and wort (W), - determining an original wort (S1) of the wort (W) or of the mixture (G) and a temperature (T) of the mixture (G) at a start time (tstart), - calculating a theoretical end time (tend) for yeast propagation based on a logical propagation model (S(t)) for yeast propagation, using the original wort (S1) and using the temperature (T) at the start time (tstart), - determining a reference value for an extract content (S) based on the propagation model (S(t)), - determining an actual value for the extract content (S) of the mixture (G) during yeast propagation, - comparing the actual value for the extract content (S) with the reference value for the extract content, and - varying between at least one influencing variable for yeast propagation depending on a deviation between the actual value for the extract content (S) and the reference value in the event that the deviation exceeds a specifiable limit value, wherein the end time (tend) for yeast propagation calculated based on the propagation signal is changed as an influencing variable, or wherein aeration of the mixture (G) during yeast propagation is set for a concentration of dissolved oxygen as influencing variable based on the deviation between the actual value (S) and reference value of the extract content and based on a content of dissolved oxygen in the mixture (G) determined during yeast propagation.

2. The method as claimed in claim 1, wherein the free amino nitrogen (FAN) of the wort (W) is determined, and is taken into account for calculating the theoretical end time (tend) using the propagation model (S(t)).

3. The method as claimed in claim 1 or 2, wherein the temperature (T) of the mixture (G) is determined during yeast propagation.

4. The method as claimed in one of claims 1 to 3, wherein an alcohol content of the mixture (G) is determined during yeast propagation.

5. The method as claimed in one of claims 1 to 4, wherein a model for an extract content (S(t)) in the mixture (G) is used as the propagation model, wherein the extract content (S(t)) is determined using the original wort (S1) at the start time (tstart), a target value for the residual yeast content (S2) and considering a substrate absorption rate (µs), a temperature rate (r) and a duration of a lag phase (λ) during yeast propagation.

6. The method as claimed in one of claims 1 to 5, wherein a starting concentration of the yeast is determined at the start time (tstart), wherein a biomass concentration (X(t)) of the yeast is determined based on the propagation model (S(t)), the starting concentration and a target value for the yeast concentration, which is linked to the target value for the residual extract content (S2), and wherein a viable yeast cell concentration is determined during propagation based on the biomass concentration (X(t)).

7. The method as claimed in one of claims 1 to 6, wherein a pH value of the mixture is determined.