3.2.1. Critical Brew House monitoring Parameters1. Temperature- Grist, Process water, Mash2. pH- brewing water & Mash 3. Time- mashing in time, time for the various rests (protein, gelatinization, Saccharification etc.)4. Saccharification- Starch Conversion to simple sugars 5. Volume- Process water, Mash6. Quantity- Raw material for accounting purposes, various brewing saltsIn most Breweries, some of these parameters (pH, Saccharification) are either checked in the laboratory or online. Only few of these parameters are checked inline (Temperature &Time). In the future, it is expected that all these parameters will be checked in-line.
Therefore, modification of the mashing plant will be required to support inline measurement. A proposed modification to support inline measurement is represented schematically in Fig. 5 below. Fig. 5: A schematic diagram of a mashing system.3.2.2 Wort Filtration Is the process of separating the sweet wort from the malt spent grains. The converted sugars are carefully leached out from the Mash and transported either to the holding vessel for temporary storage or delivered directly into the wort copper.
This process continues until the wort concentration (run-off) falls to a value at which further treatment is uneconomical. The critical analytical parameters checked are:‚§ Wort gravity (both strong wort and last running). It determines the extent to which sugars from the mash can be extracted and the time of wort boiling. Both activities are crucial to Brewhouse productivity as too low gravities requires extended boiling times for wort concentration which has both energy usage and quality implications such as high wort color formation due to mallard reaction. Prolonged filtration and boiling time extends the brewing cycle time. Wort gravity is either determined in the Lab or online after sample collection and analysis at 20oC.‚§ Wort turbidity (throughout the filtration process). This parameter is critical as too high wort turbidity has two quality implications: (1) extraction of polyphenols from the husks which subsequently leads to stability problems in the final beer. (2) trub carry over get stuck to the heating surface of the wort copper affecting heat transfer efficiency leading to extended boiling times and high energy utilization. The trub might also affect yeast cell performance by binding to the yeast surface forming flocs which causes the yeast cells to settle to the bottom of the tank much earlier than they would in the absence of trub causing fermentation problems. Wort turbidity and wort residual sludge are determined in the Lab using a density meter and Imhoff cone respectively. The results from Imhoff cone analysis takes several hours before it is available hence cannot be used in real-time process control.‚§ Wort pH: The target pH of wort after boiling is (5.1-5.3). It is believed that this pH range offers bactericidal protection of the wort which is rich in nutrients. ‚§ Temperature of sparge water (temperatures above 78oC will leach out tannis from the husk that causes flavor and stability problems; temperatures below 76oC will be ineffective in leaching out the extract from the grains. Careful control of the sparge water temperature is important for quality and efficiency of the filtration process.3.2.3 Wort Boiling Clarified sweet wort delivered to the copper (kettle) is subjected to heat treatment. In beers produced under Reinheitsgebot laws, only hops are added to an all-malt sweet wort and boiled. In other countries, additional sources of fermentable sugar in the form of liquid syrup adjuncts may be added with the sweet wort.Wort boiling serves the following functions:1) Wort sterilization and malt enzymes inactivation2) Isomerization of the Hop alpha acids giving the beer the bitter taste and contribute to beer flavors.3) Removal of undesirable flavors such as dimethyl Sulphide (DMS) from the decomposition of S-methyl methionine from the Malt.4) Wort concentration (removal of excess water to desired wort gravity) and allows correction for dilution in the mashing stage due to sparging operations.5) Helps with wort clarification (hot breaks) preventing problems in the process downstream6) Removal of oxalates which can form beer haze precipitated as insoluble calcium salt.7) Development of beer color through a process called Maillard reactions.3.2.4 Wort AnalysisWort analysis is important to determine the wort sugar composition. This is vital because the Brewing yeast is selective in its sugar absorption during fermentation. Therefore, the Brewer would be interested in knowing the wort sugar profile as it affects the beer quality. Wort contains sugars like sucrose, fructose, glucose, maltose and maltotriose together with dextrin materials. In normal situation, the brewing yeast can utilize sucrose, glucose, fructose, maltose and maltotriose in order of priority although some degree of overlap do occur. Most of brewing yeast leave maltotriose and other dextrins unfermented. Wort analysis for sugar composition is usually done in specialized Laboratories equipped with the required analytical (Gas Chromatogram). The results are not available until after a couple of days after sample collection hence cannot be used for real time decision making. Due to the complexity of these analysis, it is not done for every batch of Brews. This has led to inconsistencies in the wort composition and quality affecting the yeast performance during fermentation.3.3 Wort Treatment3.3.1 Wort CollectionThis explains the aspect of the brewing process in which wort from the Brewhouse is delivered to the fermenting vessels. The wort parameters controlled in this process are: Volume Dissolved Oxygen (DO) Specific gravity (S.G) Temperature Sterility (microbial integrity) Turbidity (Clarity)Other critical parameters to be considered are: Total time to fill the fermenter (Total filling time) Aeration rate Quantity, Sequence and timing of yeast addition3.3.2 Wort CoolingUpon completion of wort preparation in the wort copper (boil), the wort is cooled before transferred to the fermenting vessel. Both wort boiling, and cooling stages are accompanied by precipitation of solid materials called hot and cold breaks (trub) respectively which assist in wort clarification. Modern Breweries utilize inline methods of temperature control which uses enclosed heat exchangers for wort cooling. These are typically plate heat exchangers (PHE)that consist of thin stainless-steel plates with holes in each corner and a series of grooves. PHE wort coolers are highly efficient in controlling wort temperature during cooling. They are totally enclosed preventing microbial contamination and preventable wort oxygenation. As a by-product of their use, the generate hot water that could be used in other brewing processes hence reducing energy utilization. Wort cooling temperature is a critical parameter as it has a direct relationship with the wort dissolved oxygen which affects the brewer’s yeast performance during fermentation.3.3.3 Wort AerationDuring wort cooling, oxygen is added to the wort inline either as a pure gas or in the form of air as the wort is delivered to the fermenting vessel. Although wort fermentation in beer production is largely anaerobic, some oxygen must be made available to the yeast at the initial stages of fermentation for yeast cell growth and multiplication; therefore, regulation of the concentration of wort dissolved oxygen (DO) is crucial which requires that the dosing of oxygen is precise and repeatable. For fermentation to proceed rapidly, there must be sufficient amount of yeast. Inadequate growth of brewer’s yeast culture will result in poor attenuation, altered beer flavors, inconsistent fermentation times (fermentation taking longer than it should affecting equipment utilization and plant productivity). On the other hand, too much DO leads to increased yeast growth, increased higher alcohols production and reduced ester production which adversely affects the beer flavor. Therefore, an optimum amount of DO in the wort has been determined to be 8-16mg/l depending on the type of yeast strain used during the fermentation (Boulton & Quain, 2001, p.385). This DO is quickly moped off by the yeast within the first few hours into start of fermentation during active yeast growth phase. Therefore, the amount of wort DO is a critical parameter that must be recorded and monitored as it influences the yeast performance during beer fermentation.Oxygen is added to the cold wort via a stream of sterilized microbial filter. The solubility of oxygen is influenced by temperature and concentration of the wort. A desired oxygen concentration may be achieved by adding air/ oxygen at a given rate which considers temperature, gravity, flowrate and the pressure within the wort line. According to Boulton & Quain (2001) this relationship may be calculated from (p.383): RT CFW FO2 = x m3s-1 PO2 32000where: FO2= gas flow rateR= gas constant (8.3142×10-5 m3 bar/oKmol)T= Temperature at NTPPO2 = partial pressure of oxygen in the gas streamC= desired oxygen concentration (mgkg-1) FW= wort flow rate (kgs-1) If pure oxygen is used, ‘PO2 is equal to the hydrostatic pressure within the wort mains. Where air is used, PO2 reduces to the value of the hydrostatic wort main pressure x factor 0.2094″ (Boulton & Quain, 2001, p. 384).For more accurate reading, it is advisable to locate the DO meter up-stream from the gas injection point but before the yeast addition point to prevent errors of underestimation due to yeast oxygen uptake. Wort DO in breweries is determined using handheld DO meters for a given period as a given wort batch is cooled. These results are assumed to be representative of the entire batch which might not usually be the case. Incorporating an inline DO meter to monitor this critical process will have immense benefits in wort cooling process control.3.3.4 Yeast pitchingWort in the fermenter must be inoculated as soon as possible without delay, otherwise opportunistic wild yeasts and bacteria from the air in the brewery will grow in the wort in the absence of competition from actively growing cultured yeast.Yeast pitching is governed by several factors such as wort gravity, wort constituents, temperature, degree of aeration and history of the yeast. What is desired is a minimum lag phase to get a rapid start of fermentation resulting in a drop in pH which aids with stability against bacterial growth. Pitching rate employed vary from 5-20 million cells/ml depending on the wort gravity. However, pitching rate of 10-12 million cells/ml considered optimum (Boulton & Quain, 2001).The pitching rate can be determined by several methods such as turbidimeter sensors, hemocytometer and electronic cell counting. The use of commercially available in-line biomass sensor which utilizes passive dielectrical properties of microbial cells can distinguish between viable and non-viable cells and trub.A typical wort treatment line with inline wort cooling system combined with inline DO meter and inline yeast pitching meter will improve the efficiency of this process. A modification of the wort cooling system to support inline DO analysis could look like as illustrated as Fig. 6 below: Fig.6: Wort cooling system with wort oxygenation with inline O2 monitoring system and inline yeast pitching (Boulton & Quain,2001, p.385).Incorporating the data captured from Fig.6 to a data monitoring system for wort treatment displayed output will look like the diagram represented in Fig.7 below. Fig.7: Inline wort treatment monitor3.4 FermentationFermentation is defined as the metabolic process in which yeast convert sugar molecules into alcohol. In beer production the process happens under controlled conditions. The yeast breaks down pyruvate into ethanol and CO2. The biochemical reaction for this process is as follows: Brewer’s yeastC6H12O6 2C2H5OH + 2CO2(glucose) (ethanol) (carbon dioxide)Lager fermentation differs from ale fermentation in several ways:Fermentation of Lagers are at lower temperatures usually (8-12oC) resulting in a longer fermentation time, and in using a secondary fermentation, or low-temperature storage for beer maturation. Fermentation temperatures for ales are relatively higher usually (12-18oC). The yeast used in both fermentations are different as Lager fermentation utilizes bottom fermenting yeast while ales utilize top fermenting yeast.During the initial lag phase which lasts 12-24 hrs., there is often little or no observable change in the wort specific gravity, yeast count and alcohol (ethanol) concentration. The yeast cells from the previous fermentation adapt to the different conditions in the fresh wort. The Fermentation process is subdivided into two phases:1st phase: is referred to the period of active yeast growth and ethanol formation, with rapid uptake of nitrogenous nutrients from the wort. Wort dissolved oxygen concentration rapidly decreases falling to undetectable levels within 24hrs. 2nd phase: is a period of slower alcohol production with little growth of yeast/ Nitrogen uptake. It is characterized when the wort specific gravity drops to levels that are 0.5oP above the wort attenuation level (AE) and the fermentation temperature allowed to rise to 15oC, it marks the start of secondary fermentation/Ruh. It is during this period that most of the fermentation bye-products like diacetyl that will affect the beer flavor stability are removed by the yeast (maturation stage).Fermentation of sugars to alcohol eventually stops due to one or more of the following: Exhaustion of fermentable sugars, Inhibition of yeast by alcohol, Settling or flocculation of the yeast cells.For this research, fermentation management will be subdivided into two sections: ‚§ Monitoring Fermentation Progress Monitoring Temperatures Monitoring CO2 evolution rate Monitoring exothermy Monitoring pH Monitoring rate of O2 assimilation Monitoring yeast growth Monitoring Ethanol Formation Monitoring Vicinal diketone concentration‚§ Fermentation Control Temperature Yeast Pitching Rate Wort Dissolved Oxygen Pressure