Milling Mashing and Yeast Fermentation 2020-2-2.pdf

MILLING, MASHING, BOILING & YEAST FERMENTATION Brian Freeland X205, [email protected], ext: 8515 Malt is taken into the brewhouse and stored in silos (large operations) or in sacks (small operations). Adjuncts are also stored in bulk or in sacks. Granular sugar is stored in sacks and liquid sy...

MILLING, MASHING, BOILING & YEAST FERMENTATION Brian Freeland X205, [email protected], ext: 8515 Malt is taken into the brewhouse and stored in silos (large operations) or in sacks (small operations). Adjuncts are also stored in bulk or in sacks. Granular sugar is stored in sacks and liquid syrups in tanks. Malt is taken from the storage area and weighted en route https://www.youtube.com/watch?v=xdh4RBwX 6mo Any metal is removed by a magnet Malt is destoned https://www.youtube.com/watch?v=HStjMUEY Rcs MILLING Only malt free of metal, stones, stalks and other foreign material is sent to the mill. https://www.youtube.com/watch?v=WD_TlpOHZfM The milled grain is sent to a grist case (this is equipped with strain gauges which weigh the grist again) From the grist case the grist is mixed with brewing liquor in a Steeles Masher. The starch from the malt is converted to fermentable sugar in the mash. When all the starch has been converted to sugars the wort is separated from the grains using either a mash tun, lauter tun or mash filter. The sweet wort is then boiled with hops in the kettle. The unwanted solid material, the spent grains, are normally used for animal feed. During the boil lipid and protein material coagulate and form hot break. This is removed in from the wort using a whirlpool. The wort is then cooled, some air is added to the wort, and yeast is added to the wort to initiate fermentation. WORT PRODUCTION At the end of fermentation the beer is known as green beer. To develop the final flavour the green beer is matured. FERMENTATION The beer is filtered, stabilized against haze, carbonated and sent to the Bright Beer Tank (BBT) before being packaged. https://www.youtube.com/watch?v=Lo2LNHqDt8 BREWING GENERAL PROCESS MILLING Storage: •Silos can be made from steel or concrete. •Must have smooth walls with hopper bottoms to ensure easy grain withdrawal. •Malt and cereal adjunct must be stored at the correct moisture level to ensure . GRAIN HANDLING IN BREWERIES Temperature control is important in order to control the growth of pests Enough quantities of malt must be stored in the brewery for about 5 days production needs. PARTICLE REMOVAL FROM GRAIN • Screening: Consistency of size of corns. • Malt must be screened to remove small or large corns. • Dressing: this is the removal of unwanted material such as straw, stones, string, sacking and metal particles. https://www.youtube.com/watch?v=WD_TlpOHZfM • De-stoning: the separation is based on density. In this way small stones of the same size as the malt grains can be removed. • All metal must be removed before the mill because such metal can cause a spark and start a fire or explosion. • Separation is accomplished by placing permanent magnets either in the malt chute or screening machine or across the feed to the mill. • Malt should flow over the magnet in a think layer at the same rate as it is being ground, thus allowing the magnet to extract any ferrous metal that may be in the malt. MILL SAFETY Malt Mills Risk Mitigation • Magnets (prevent sparks). • Stone separators (prevent sparks). • Explosion doors. • Safe systems of work. • Good housekeeping. • Noise is a hazard (ear protection) •Inhalation of dust (dust masks). MILL TYPES – FOUR ROLL MILLS • Can be used with • Well modified ale malt. • mash tun compatible. • How it works: 1. Feed roll controls flow of malt to the mill. 2. First (upper) pair of rolls crack open the malt. 3. Beaters and separation screens send fine particles and husks straight through to the discharge. 4. Coarse particles go to the second pair of rolls. 5. The second pair of rolls crush the coarse particles. MILL TYPES – SIX ROLL MILLS • Can be used with: • Less well modified malts, Starch needs to be finely ground to allow rapid wetting. • In order to protect the husk the malt may be “conditioned” with steam or warm water prior to milling. (this softens the husk and its less likely to break into small pieces). How it works: 1. The feed roll control the flow of malt to the mill Upper pair of rolls crack open the malt to release the endosperm. 2. The upper screen sends the flour straight through to the discharge and the course particles go to the second pair of rolls. 3. The second pair of roll crush the coarse particles. 4. The lower screen sends the flour to the discharge. Husk straight across the screen to the discharge and the grits to the third set of rollers. 5. The third set of rollers crush the grits to produce fine grits. MILL TYPE – WET MILL • Used for lager production. • The husk received extra protection as its pre-steeped in water before milling. • Single set to rolls. MILL TYPESHAMMER MILL • Used in conjunction with a mash filter. • Produces a very fine grind. • Leads to good wetting and subsequent enzyme activation. • Rapid extraction of sugars from the particles. • https://www.youtube.com/watc h?v=rzLVONmwP3g ANALYSIS OF GRIST • The quality of the grist (crushed malt) has a major effect of the performance of the brewhouse. • Too coarse: • starch remains protected and the enzyme will not be able to access the starch Poor extract efficiency Poor run offs • Too fine: • Wort separation will be slow (filter bed chocked) ANALYSIS OF GRIST • https://www.youtube.com/watc h?v=x1Ch2oEd_wg Grist requirement for various mash equipment MASHING MASHING OBJECTIVES • The ground malt (and ground adjuncts) are wetted in a Steeles masher before entering the mashing vessel. • This is left to stand at a particular temperature (or temperatures) for around an hour in the mashing vessel. • Until all the starch has been converted to sugars. MASHING OBJECTIVES • Biochemical changes during mashing: • Cell wall components may be broken down to release starch (under modified malt). • Proteins are broken down to amino acids. • Starch is converted to sugars. • The pH drops. MASHING PROCESS The mashing step uses enzymes to break down starch to sugars, the enzyme reactions are dependent on: 1. The substrate and enzyme available. 2. The duration of the temperature stands. 3. The pH of the mash. 4. The mash temperature. 5. The water to grist ratio. AT THE END OF MASHING, WORT SHOULD CONTAIN • A range of sugars. • Proteins which will help form foam. • Amino acids which allow yeast growth. • Lipids and fatty acids which allow healthy yeast growth. • Mineral salts and vitamins which allow healthy yeast growth. MASHING OVERVIEW The goal of the mash step is to enable the starch conversion to sugars such as: fermentable sugars like maltose and glucose. Polysaccharides (dextrins) which offer mouthfeel and body of the beer. During the mashing • The grist is mixed with water in a mash conversion vessel (stirred) or a mash tun (grain bed is raked) and heated for an hour. • Once the mashing is finished, the grain is separated from the liquid phase in the lautering process, which is equivalent to a cake-filtration. • The grain is disposed (usually used as animal feedstock). • The gathered liquid is called the wort and is carried to the next step. MASHING - ENZYME ACTIVITY • During the mashing, α & β amylases are released from the aleurone layer in the grain. • Enzymes break grains glycosidic bonds to produce the smaller sugars. • Those enzymes have different mechanisms, • α-amylase cut starch in large fragments (dextrins). • β-amylase will cut starch and dextrins into maltose from the end of the polysaccharide chains. MASHING - ENZYME ACTIVITY • Each enzyme has a specific optimal working temperature range • allows the brewer to tune the degree of fermentability of the wort. β-amylase, optimal temp = 62°C • Mostly maltose and glucose produced. • the wort will be very fermentable. • Yielding in a “crisp” beer. α-amylase, ideal temp = 67°C, • Mostly dextrins produced. • The wort produced would be more complex and “heavier” in taste. • Less alcohol would be present in the final beer. • Usually brewers would choose a stepped heating. MASHING OUT • Mash-out – mash complete • heat the worth to 78°C to inactivate the enzymes PROTEIN REST STEP • Additional possible step at start of mash: • If the malt is under-modified (starch is not available in the grain). • a “β-glucan rest or protein rest” in a temperature range of 48-52 °C • allows the β-glucanase along with proteases to break the cell walls in the endosperm of the grain. • Step allows for a better overall efficiency of the mashing. • But is not conduced often nowadays due to the improvements of malting technology (well-modified malt). Mash Stage Cell wall structure breakdown Active Enzymes Endoglucanase, beta solubilase, phosphatase Activity Range (°C) Effect on Mash 40 – 53 Starch granules in the grains are protected by a cell wall which has to be broken down before the starch can be converted. Protein breakdown Endo-peptidase, carboxy-peptidase, amino-peptidase, dipeptidase 45 – 50 At this stage of the mash the water-insoluble protein sheath is penetrated, allowing the starch to be reached. Protein molecules are broken down into their constituent amino acids which are necessary for healthy fermentation. Starch breakdown Beta-amylase, alpha amylase, limitdextrinase, maltase, saccharase 35 – 75 Starches are broken down into fermentable sugars. MASH TEMPERATURE STAGES STEP MASHING TEMPERATURES • Chart illustrated the effects temperature and pH when mashing. • The ideal mashing temperature is between 65°C – 68°C (149°C – 154°F) • At these temperatures, the beta amylase and alpha amylase enzymes are activating which are the enzymes most effective of converting starches into fermentable sugars for fermentation. EXAMPLE PROGRAMMED STEP GERMAN FESTIVAL BEER RECIPE – FESTIVAL BEER FROM SPEIDELS BRAUMEISTER INGREDIENTS 55 l of brewing water to start with plus sparging water 5.5 kg Pilsner malt 5.5 kg Munich malt 1.0 kg Carapils 100 g Tettnang hops (4.2 % alpha) 1 packet Saflager S-23 yeast METHOD HOP ADDITION 75 g Tettnang hops › 70 min before end of boil 25 g Tettnang hops › 10 min before end of boil ORIGINAL GRAVITY 12 ºP with 52 litres FERMENTATION Fermentation temperature at around 12 °C MATURING 2-3 days at room temperature, followed by 3-4 weeks in the refrigerator at 5 °C HTTPS://WWW.SPEIDELSBRAUMEISTER.DE/FILES/BRAUMEISTER/DOWNLO ADS/BRAUREZEPTE/FESTBIER/EN/SPEIDEL_BREWI NG_RECIPE_FESTIVAL_BEER_BM_50-LITRE.PDF CONTROL PH IN MASH • For mashing, the ideal pH = 5.2 - 5.5. • This pH should be approx. 5.5 for fermentation. • When sparging the pH of the run-off is tested • if pH > 5.8, tannins are being extracted which lead to a harsh astringency in the final beer. • At the end of fermentation, pH = 4.2 – 4.4. • Berliner Weiss, pH = 3.2 which is what gives the beer its tart, sourness. • The supply water should be tested and treated to maintain a pH of 5.5. MASH TUN VESSEL • Isothermal (single temperature) mash. • This vessel combines mashing and wort separation in a single vessel. • Well modified malt can only be used in this system as there is no facility for heating the mash. • No heating jackets on vessel. • No mixing mechanism. • Wort may become stuck. • Brewhouse extracts with this system are lower than those obtainable with lauter tuns or mash filters. • There simplicity makes them ideal for small operations. MASH TUN ISOTHERMAL INFUSION MASH Temperature ramp – no steps. MASH TUN S U M M A RY MASH CONVERSION VESSEL (MCV) – A MODERN APPROACH • The MCV is fitted with heating. • Mixing facility. • Less well modified malt can be used. • Mash must be transferred to another vessel for separation. • It can be linked to a mash cooker (decoction systems). • It can be linked to a cereal cooker. ISOTHERMAL VS PROGRAMMED/STEPPED MASH INFUSION MASH VS PROGRAMMED/STEPPED MASH ASSESS STARCH CONVERSION OF MASH • At the end of mashing check that all the starch has been converted. • Iodine test (0.02 N iodine solution). WORT SEPARATION • Methods • Mash tun • Lauter tun • Mash filter Lautering is a process in brewing beer in which the mash is separated into the clear liquid wort and the residual grain. Lautering usually consists of 3 steps: mashout, recirculation, and sparging. WORT SEPARATION – USING THE MASH TUN • The mash tun serves as a conversion vessel and a separation vessel. Separation • Wort is run off through one or more discharge pipes, each pipe serving the same area of • the base. • The wort may be recycles to the top of the mash until it runs clear. • The rate of run off is controlled using a weir or a single flow control valve or a series of • valves at different heights • Strong wort run more slowly as it is viscous and the bed must not settle onto the plates • When the strong wort have been run off but before the bed has settled on the false floor the • sparge is started. • The rate of sparge addition is the same as the rate of run off. • Once a fixed volume of sparge has been added the tun is allowed to drain down. WORT SEPARATION – LAUTER TUN VESSEL Operation 1. 2. 3. 4. 5. Lauter false floor is flooded with water. Rakes moved to highest position. Converted mash transferred to the LT from bottom of LT When LT is almost full recirculation of cloudy wort starts. The rakes are used to spread the mash across the false floor at this stage, however they are then returned to their highest position. 6. Cloudy worts arise from under the bed and from fine material in the bottom layers of the bed. 7. Run-off starts when the wort is clear. 8. During lautering the rakes are operated (height and speed varied) in oreder to keep the differential pressure constant. 9. After the strong wort has been run-off but before the top of the bed runs dry – sparging begins(sparge addion matches run-off rate). 10. The bed must not be allowed to dry out as this would cause bed compaction and oxygen pick up. 11. Sparge volume is fixed and when the allowed amount has been added the bed is allowed drain without restriction M A SH FI LT E R • https://www.youtube.com/watc h?v=szQa9f6xBMI WO RT SE PA R AT I O N SUM M A RY • Description of the main differences between wort separation systems. BOILING WORT BOILING Purpose of wort boiling • Sterilize the wort. • Stabilize the wort. • To evaporate and concentrate the wort. • Dissolve the bittering resins. • Dissolve the oils. • Denature and coagulate. • Develop wort colour and flavour. • To increase the strength or concentration of the wort. • pH of wort falls during boiling. • Addition of sugar adjuncts. FACTORS THAT EFFECT WORT BOILING EFFECTIVENESS DURATION TEMPERATURE INTENSITY CIRCULATION CURRENTS CONDENSATION OF VOLATILES WORT BOILING – PURPOSE OF SOLID AND LIQUID SUGAR ADDITION • Flavour • Lighter smoother flavour (bland adjuncts) •Distinctive flavour (flavoursome adjuncts) •Carbohydrate : Nitrogen ratio (this will affect fermentation products) • Benefits to the Brewer • Better extract recovery • High gravity beers • Increase in brewhouse capacity •Avoidance of capital expenditure •Lower LT loadings (faster run-offs) WORT BOILING SYSTEM – DIRECT FIRED MICRO-BREWERY • A typical installation in a microbrewery is shown. This uses a gas or oil burner (rather than a fire box). Heating is via internal heating coils. This give poor recirculation but its better than the situation when using a fire box. The heat transfer is more efficient than the fire box system as the coils are surrounded by wort. • The use of steam and internal heating systems provide a larger heating are than the fire box. The heat transfer in these kettles is more efficient as the coils are surrounded by wort. • Two types: • Heating element inside the vessel (a) this shows a simple spiral looped internal coil. • Heating element outside the vessel. WORT BOILING SYSTEMS: DISADVANTAGES OF HEATERS WITH INTERNAL TUBES • Difficult to clean with CIP (blind spots). • Corrosion can lead to leaks. • Turbulence over heating surface is limited. • High levels of fouling • More frequent cleaning required to ensure effective heat transfer. WORT BOILING SYSTEMS: ASYMMETRIC COPPER • Forced recirculation (agitation) – this improves turbulence and recirculation. • Chimney. • Spreader plate. WORT BOILING SYSTEM: MODERN DESIGN – KETTLE WHIRLPOOL • Shell and tube heat exchanger: steam supply is contained within the shell whilst the wort passes within the tube. • Minimizes fouling. • External heaters: wort is taken out of the kettle and passed through a shell and tube heat exchanger for heating. The heat exchanger may be primed using a small pump pre-boil. • Reintroduction of the wort tangentially makes it possible to use the vessel in a combined kettle /whirpool. • This eliminates the transfer times between a separate kettle and whirlpool. WORT BOILING SYSTEMS: ENERGY CONSUMPTION • Wort Boiling consumes about 30% of the thermal energy used in a brewery. With the increasing cost of fuels recent designs have concentrated on being as energy efficient as possible. • Evaporation rate have been reduced from 10% to 4% (with energy recovery) 2% (without energy recovery). • High levels of insulation. • Designed to avoid the build up of soil, particularly on heating surfaces •Heat recovery to generate hot water. BOILING ADDITIONAL NOTES 1 • As the name suggests, this step consists in bringing the wort to a boil temperature and maintain it for an hour or more. Even if very simple, this procedure will have a major influence in the flavour, appearance and shelf-life of the beer. During this phase the wort is transferred to an industrial kettle and heated. Due to the 100°C temperature, the wort is lightly sterilised (spores of several microorganisms can still survive) and the pH is decreased to a range more suitable for fermentation (4.5 to 5.5) due to calcium salts reacting with polypeptides and phosphates releasing H+ ions. In addition, the enzymes and other proteins are denaturated and precipitate (hot-break), the colour is further developed due to Maillard reaction, and the specific gravity of the wort is increased due to water evaporation. • However, the key element of the boiling phase is the hop addition. Hops are the flowers (cones) of a plant called humulus lupulus. The cones contain a singular mixture of chemical compounds that act on the flavour and bitterness of the beer. The principal molecules of hops are humulones also called α-acids and lupulones or β-acids. These molecules act as a anti-bacterial agent for Gram-positive bacteria (Listeria, Lactobacillus, Streptococcus …) and also as an anti-fungal agent against Candida, Fusarium, Trichophyton and other potential pathogens. The α-acids are the main actors for the bitterness of the beer as they undergo a heat-induced isomerisation during the boiling which produces iso-α-acids who are much more bitter compounds. • Specific gravity (abbreviated SG) is a measure of the density of a fluid, it is made with a hygrometer or a vibrating U-tube densimeter. It is the method of choice for brewers to measure the fermentability of the wort because of its simplicity of use and the fact that it correlates accurately with the amount of carbohydrates in the beer or the wort. The fermentation is usually monitored with SG since it allows to know when the sugar conversion is finished. The difference between the original gravity (OG, measured post-boiling) and final gravity (FG, measured post-fermentation) is used to estimate the percentage of alcohol in the beer. BOILING ADDITIONAL NOTES 2 • EFFECTS OF INADEQUATE AND OVER BOILING: • When boiling the wort, you may think that so long as the liquid gets really hot for some time then the boiling stage has been taken care of and all is well is for the rest of your brew. • But as with all stages in home brewing, a slight lack in judiciousness can cause an inferior result in the end. • When the boil has been inadequate a number of problems may become present, such as; • Lower gravity • Poor separation of trub from the wort • Poor fermentation and filtration difficulties • Higher than acceptable DMS levels • Poor hop utilisation • Susceptibility to contamination • When boiling for too long or even sometimes overheating, there are also other negative effects that may occur such as; • Higher gravity, lower volume of wort • Trub breakup causing haze and flavour problems • Harsh bitterness • Increased wort/end beer colour • Boiling contributes significantly to the final wort composition, which in turn controls many of the factors in flavour, body and palate fullness of the final beer. HOP ADDITION • A key element of the boiling phase is the hop addition. • Hops are the flowers (cones) of a plant called humulus lupulus. • The cones contain a singular mixture of chemical compounds that act on the flavour and bitterness of the beer. • The principal molecules of hops are humulones also called α-acids and lupulones or β-acids. • These molecules act as an anti-bacterial agent for Gram-positive bacteria (Listeria, Lactobacillus, Streptococcus …) and also as an anti-fungal agent against Candida, Fusarium,Trichophyton and other potential pathogens. • The α-acids are the main actors for the bitterness of the beer as they undergo a heat-induced isomerisation during the boiling which produces iso-α-acids who are much more bitter compounds. HOP ADDITION TO BOIL – HOP OILS • Hop oils are the aromatic fraction of the resins and give the beer its hoppy “nose” and character. • These are very volatile and will be lost during the boil unless they are added late in the boil. • Beers with a strong hop aroma will most likely have been late hopped, dry hopped (added to the fermentation vessel or into the cask. • They could also have had addition of hop oil during beer processing HOP ADDITION TO BOIL – CLASSIFIC ATION OF HOPS • Hops belong to two usage groups • Bittering hops • Aroma hops • Recently agronomic developments have given rise to a number of hop varieties which a considered suitable for either or both uses. • Bittering hops are bred for high alpha acid content. These can be used for preparing extracts, when any undesirable aromas are lost, or may be added at the start of the boil when any undesirable aroma characteristics are boiled off • Aroma hops have been bred primarily for the desirable hop oil content. Sometime these varieties also have high alpha contents. HOP ADDITION TIMING • Isomerization is a relatively rapid reaction. • 90% of the wort bitterness occurs during the first 30 minutes of boiling. • Complete extractable bitterness occurs within 60 – 70 minutes. • The isomerization reaction is faster the higher the temperature. COOLING Once the boiling is finished, the wort is clarified by whirlpooling (most used) or sedimentation. It is cooled to a temperature of 15 °C for ales and 8 to 10°C for lager (two main beer classes due to a difference in the yeast type) with a plate exchanger and transferred to the fermentation vessel. WORT COOLING NOTES Because of the cooling, some larger polypeptides who were soluble when the wort was hot will precipitate (cold break). Along with the hot break, these solids represent approximately 17 to 32 % of the total proteinic content from the grain. At this stage the wort can also be filtered to remove the cold break before fermentation. WORT CLARIFIC ATION NOTES • Wort forms a precipitate during both the boil stage (break) and when cooling prior to fermentation (trub). • This precipitation is insoluble and consists of; • Hardened protein, Polyphenols (tannins), Carbohydrates Clarification steps: • Why clarify? - Trub effects beer quality in a number of different ways • There is a direct correlation between beer flavour instability and trub reduction, • where some of the trub components are substances that can induce negative flavours later in the beer. • Trub has a significant concentration of bitter and polyphenolic substances which can impart on the flavour of the beer if left. • Haziness can also be introduced into the beer if trub is left in the wort. • Fermentation can also be affected by trub, where a yeasts health that gets re- pitched over time will compromised. TRUB REMOVAL • During the ‘hot break’, but Cold trub removal is also possible but is not always as practical. • If you are using the Grainfather or similar system either ‘filtration’ or ‘whirlpooling’ become your best options. YEAST FERMENTATION Relationship to other organisms • Eukaryotic • Microorganism BREWING YEAST • Fungi (plants that don’t photosynthesise) Single celled fungus • Grows aerobically (with air) • Grows anaerobically (without air) TOP AND BOTTOM FERMENTING YEAST • When oxygen is available yeast respires NUTRITIONAL REQUIREMENTS OF YEAST • When No Oxygen is available Yeast Ferments • When operating aerobically • WARNING! Acetaldehyde formation during yeast propagation. NUTRITIONAL REQUIREMENTS OF YEAST • During yeast propagation the aim is to obtain maximum yield of yeast but also to keep the flavour of the beer similar to a normal fermentation so that it can be blended into the production stream. • Intermittent aeration to stimulate growth is used but not so much that excessive acetaldehyde is produced. (flavour threshold of acetaldehyde is approx. 5 ppm. • Other nutritional requirements of yeast: NUTRITIONAL REQUIREMENTS OF YEAST • Amino acids. • Lipids or fatty material Vitamins. • Trace metals (Ca, Zn, Cu etc. Oxygen (for making sterols). BEER FLAVOR COMPOUNDS 1. Esters - as an example • Reaction of alcohols with organic acids • Fruity flavours (tropical fruit) • Ethyl acetate (boiled sweet flavour) • Iso amyl acetate (bananas or pear drops) • Ester formation is towards the end of fermentation • Esters are formed when yeast stops making fats • More yeast growth more esters • HGB produces high levels of esters • Ratio of fermentable sugars to nitrogen FAN main • determinants of ester levels in beer • The more yeast growth the less esters • Increased temperature increase ester production • Increased pressure during fermentation decreases ester formation. BEER FLAVOR COMPOUNDS • 2. Higher Alcohols (Fusel Alcohols) • Flavour of alcohol or winey. • Iso-butanol and iso-amyl alcohol. • Produced as by products of protein synthesis. • Total amount produced directly related to the amount • of yeast growth: • Increased level of wort oxygen • High levels of FAN • Increase fermentation temperature • Increase pressure decreases higher alcohol production. Very tall fermentation vessels tend to produce less higher alcohols and esters because of the increase hydrostatic pressure. BEER FLAVOR COMPOUNDS • 3. Diacetyl • Toffee or butterscotch flavour. • Desirable at low levels in ale. • Not desirable in lagers (<25ppb). • Produces during fermentation but the yeast re – adsorb it and convert it to flavour neutral compounds during the conditioning phase. • It is the diacetyl level (measured by the lab) that will determine when a beer is moved from the FV to the maturation phase of the process. BEER FLAVOR COMPOUNDS • 4. Sulphur Compounds • When present at high levels – unpleasent off• flavours • Fermentations must be managed to ensure • levels are below flavour thresholds in beer especially: • H2S (rotten eggs) • SO2 (burntmatches) • Both these compounds are by-products of the synthesis of sulphur containing amino acids • Management S -Compounds in FV Sufficient CO2 evolution Extended maturation time • Do not allow yeast to sit on attenuation limit BEER FLAVOR COMPOUNDS • 4. Sulphur Compounds Di Methy Sulphide (DMS) • Principally derived from malt • DMS smells like tinned sweetcorn • Rarely detectable in ales (removed during • kilning) • Intentionally present in lagers • Flavour threshold of 30ppb • Can be removed during the kettle boil • Some yeast can produce small amount of • DMS • Management DMS levels in Beer •Specify levels in malt •Wort boiling condions MAIN PHASES IN F E R M E N TAT I O N GROWTH PHASE • Usually log increase in cell concentration. • This starts after the lag phase (usually between 6 to 12 hours after pitching). • Yeast cells start to grow (budding) and the specific gravity decrease slowly. • Growth phase continues for about 24 to 48 hours. GROWTH PHASE • Growth is limited by: •Dissolved Oxygen •Nutrients • When yeast cell numbers reach their maximum the specific gravity drops rapidly and this is the fermentation phase. • The pH of the wort drops from 5.2 to about 4.0. RETARDATION PHASE • The growth phase is followed by a retardation phase (late in the fermentation). • Growth is limited by: • Available fermentable sugars • Increase in alcohol • Settling of the yeast (flocculation) STATIONARY PHASE • The rate of cell death exceed the rate of new cell formation. • The final stages of fermentation are slow and it is where the yeast “mop up” the available nutrients that are available. • The most important biochemical reaction that occurs at this stage is the removal of diacetyl. • Top fermenting yeast may be removed at this stage. • The beer may be cooled. FACTO R S T H AT A FFECT FER M EN TAT IO N P H A SES Pitching rate. Yeast strain. Age of yeast (how long it has been stored for). Wort oxygenation level. Wort temperature. Wort composition. Sugar concentration. The amount of alcohol produced (different yeasts have different tolerances to alcohol. Mixing in the Fermentation Vessel. Yeast strain. Fermentation Vessel design. FACTORS THAT AFFECT SPEED OF FERMENTATION Pitching rate. Wort Dissolved Oxygen. Final temperature. Initial temperature. Top heat. Rate of temperature increase . Initial temperature of the wort.