Chemical Foodsuffs Processing. Chapter 8

Beer brewing is an intricate process encompassing mixing and further elaboration of four essential raw materials (barley malt, water, hops and yeast) 1 Introduction to fermentation Fermentation is a reaction wherein a raw material is converted into a product by the action of micro-organisms or by means of enzymes. Microbial fermentations promoted by micro-organisms. At first, the rate of conversion of raw materials to products is low because the microorganisms are few i.e. the catalytic agent is small. As more micro-organisms are formed, the rate starts to rise. The rate then reaches a maximum when there is optimum ratio of unconverted material and the micro-organisms. The rate then drops as the raw material becomes depleted. Finally the rate stops when the raw material is finished. 2 Enzymatic fermentations : catalyzed by enzymes Enzymes are proteins which occur in nature in micro-organisms, animal organs and vegetable extracts. They are biocatalysts which bring about specific biochemical reactions without their structure or quantity being changed.  Their activity depends on temperature, pH, storage time and storage conditions. Because of their specificity, only one product is produced from a selected enzyme and therefore, purification is less expensive than microbial fermentation. For microbial fermentation route to be economically attractive for a given product: ⸻ There must be a microorganism that will form that product. ⸻ The microorganism must be readily propagated to give consistent yield and quality ⸻ Raw materials must be available cheaply in uniform composition. ⸻ The yields must be economically acceptable. ⸻ Product recovery and purification should be easy 3 Factors that affect fermentation yield Inoculum amount, i.e., the initial amount of cells fed into the fermenter, will determine whether the cells are sufficient or not to fuel production. Initial level of contamination brought in by the raw materials or found in equipment and pipelines. The contaminating microorganism will feed on the raw materials and produce other products. Equipment and substrate should therefore be sterilized before inoculation. pH level will determine whether contaminants will multiply or will be repressed. For example, yeast grow best at pH 4-5. It is important to exploit pH tolerance of microorganisms. Acid by-products may be neutralized by adding ammonia, calcium carbonate or calcium hydroxide 4 Cont’d… Temperature: The best temperature for culturing the micro-organism varies with the species. It is important to study temperature tolerance of micro-organisms. Since heat is produced during fermentation, temperature control is necessary to maintain optimum activity of microorganisms. Product concentration may increase to a level that inhibits the activity of micro-organisms. The initial concentration of the raw material (substrate), for example sugar may be too high and therefore adversely affect the micro-organisms. Micro-organisms vary in their need for Oxygen. Fungi, algae and a few bacteria are aerobic while a few bacteria are anaerobic. For those which are aerobic, a too low oxygen level leads to “poisoning” of fermentation while too high oxygen content causes excessive growth of microorganisms at the expense of the product. 5 Sterilization for fermentation A) batch sterilization purging steam using an electric element to heat the medium through a jacketed vessel to raise the temperature during the sterilization. Cooling water through the jacket brings down temperature to be optimum for fermentation. B) Air sterilization: using air filters to remove air-born microorganisms from the air along with large particles in laboratory – using cotton plugs in pilot plant (i.e., small scale fermentors) – small fibrous filters Large industrial fermentors – heat may be used to sterilize air. 6 Fermentation process • alcohol is produced by the action of zymase enzyme on certain sugars (i.e., glucose). • Zymase is secreted by the microorganisms known as yeast that uses to decompose a solution of glucose into alcohol and CO2. C6H12O6 Zymase 2C2H5OH + 2CO2 The microorganism “yeast” is not only secret the enzyme zymase; it also secrets invertase and maltase. C12H22O11 + H2O invertase C6H12O6 (glucose) + C6H12O6 (fructose) 7 Cont’d…. • Starch also contain fermentable sugar mainly from rice, wheat, barely and maize. 2(C6H10O5)5 + nH2O (glucose) Zymase Diastase enzyme nC12H22O11 (maltose) Maltase 2 C6H12O6 4C2H5OH + 4CO2 The enzyme diastase is contained in malt which is produced during germination of barely. After drying of the malt obtained during germination is conditioned at increased T0 (70 0C) and then allowed to rise to 90 0C (this process is called curing → killed malt is obtained) 8 The basic steps of brewing beer are:- i. Malting -Liberate enzymes (diastatic power) ii. Mashing - Enzymes convert starch to sugar iii. Drain liquid –wort iv. Add hops (flavoring) v. Fermentation - “green beer” vi. Aging (“lagering”) vii. Pasteurization/filtering viii. Re-addition of carbon dioxide ix. Bottling 9 Cont’d… (1) Malt- contains starch and small amount of sugar, together with the enzyme diastase, is crushed and mixed with hot water and raw grain or potato starch is then added. T0 is maintained at 40-60 0 C. As the result of fermentation in the presence of diastase, starch is converted into malt sugar (the process is called mashing). Varying conditions during the process (T0 and humidity) allows different types of malt to be obtained, giving different colours and flavours to the beer 10 Cont’d… (2) The hop (humulus lupulos): is an aromatic plant that gives beer its flavour and bitterness. It contributes to the formation of a good froth and protects the beer against contamination by microorganisms. • The hop acids have pronounced bacteriostatic activity • During boiling of hops in wort many constituents are volatilized or oxidized and the hop- derived constituents present in beer are different from the original molecules. (thermal isomerization of the alpha-acids or humulones to the iso-alpha-acids or isohumulones leads to bitterness). 11 Cont’d….  In addition to imparting bitter taste to beer, the iso-alpha acids exhibit tensioactive properties, thereby stabilizing the beer foam, and inhibit the growth of Gram-positive bacteria, thus protecting beer against these micro-organisms. • The beta-acids are very sensitive to oxidative decomposition and most oxidation reaction products possess unpleasant organoleptic characteristics (less optional to be used).  Hop polyphenols are found as monomers, dimers, trimers, but also as more complex forms associated with nitrogenous components. It is common practice to distinguish between ‘chill haze’ and ‘permanent haze’. 12 Cont’d…. • The polyphenols combine slowly with proteins to form chill haze when cooled, but which re-dissolves when warmed up. As the polyphenols polymerize and grow larger, they become insoluble at room temperature to form irreversible haze (permanent haze). • The extent to which a beer requires stabilization depends on its shelf-life and the storage conditions after packaging. It appears that hop polyphenols are a group of substances with interesting effects on taste and taste stability of beers. 13 Production Process 1. Preparing the Wort The first phase in the process of beer production is the preparation of the wort. This process has four stages: Milling: In order for the malt components to be rapidly extracted and converted, the malt is milled to obtain coarse flour. Mashing: The flour from the cereals (malt and other unmalted cereals) is mixed with water and subjected to certain processes to obtain a wort of a suitable composition for the kind of beer being produced (varying times, temperatures and pH). Mashing lasts 2 to 4 hrs and finishes with a T0 of approximately 75 ºC. Filtration of the wort: The whole volume is filtered in order to separate the spent grains from the wort itself. This is done by passing water through the mash at the right temperature in a filter press or lauter tun, which lasts around 2-3 hours, conducted at a temperature of 75-80 ºC. What type of enzyme is secreted during malting and why killed malt is needed during beer production?? 14 Cont’d…. Boiling the wort: The diluted and filtered wort is boiled for ⁓2 hours. Hops are added at this stage. The purpose of boiling is to: Transform and make soluble the bitter substances in the hops (i.e. extraction); Eliminate undesirable volatile substances; Sterilise the wort; Provoke the precipitation of proteins of high molecular weight; Establish the final concentration of wort. After boiling, it is necessary to separate the precipitated protein and the insoluble hop components from the hot wort. Separation may be carried out in a decanter using gravity or with centripetal force in a "whirlpool". Before the hopped wort goes into the fermentation tanks, it is cooled to a temperature of around 9 ºC and aired in sterile conditions. 15 Production process (Cont’d…). 2. Fermentation/Maturation/Stabilisation Fermentation: The wort sugars are converted into ethanol (C2H5OH) and CO2 by the action of yeast . Fermentation begins when yeast of a culture selected for the type of beer being produced is added to the cooled oxygen-saturated wort. Fermentation takes place at controlled T0 and lasts around 7 days. At first it is quite violent, then slows down gradually until the yeast is deposited on the bottom of the tank. Maturation: the phase after fermentation, is the period in which the beer is allowed to rest at suitable temperatures in order for the undesirable volatile components, which might affect the final «bouquet» of the beer, to be released. The next operation is stabilisation, consists of letting the beer stabilise at T0 of between 0ºC and - 2ºC, to permit colloidal stabilisation. 16 Cont’d…. 3. Clarification of the Beer Clarification: is the operation that gives the beer its clear limpid quality, eliminating the last remaining traces of clouding still in suspension. It consists of pumping the liquid through a suitable filter. The filtered beer is then stored in tanks, now ready to be bottled. Filtering media: diatomaceous earth Bottling The final stage of the beer production process is transferring the beer into different kinds of containers (bottles, barrels, cans etc). Before or after bottling, the beer needs to be biologically stabilised. This operation may be carried out cold (sterilising filtration) or hot (using pasteurisation, which may be done either immediately before (flash pasteurization) - or after the drink is introduced into its container (tunnel pasteurisation). 17 Cont’d… • CO2 Leftover from fermentation contributes to taste and freshness flavor to the young beer. • O2 Contributes to aging and spoilage (fasten the beer to be expired its shelf life). 18 Off flavor of beer • Iso-alpha-acids are partly responsible for production of ageing off-flavours, including stale and cardboard flavours. • this is due to vulnerability of the iso-alpha-acids to light. The resulting decomposition leads to formation of the so-called ‘light struck flavour’. • The light sensitive chromophore in the isohumulones is the acyloin group composed of the tertiary alcohol function at C(4) and the carbonyl group of the side chain at C(4) • The isohumulones with UV light causes bond cleavage by a Norrish Type I reaction, leading to a ketylacyl radical pair. Subsequent loss of carbon monoxide from the acyl radical and recombination of the resulting fragment with a thiol radical furnish 3methylbut-2-ene-1-thiol, also known as ‘skunky thiol’. 19 Cont’d…. The flavour threshold of the thiol is so low that even concentrations of few ppb spoil irreversibly the beer quality 20 Cont’d.. • Volatile aldehydes, such as trans-non-2-enal, are formed during storage of bottled beer from various precursors, including hop lipids. • Thus, beer must be stored, either in opaque cans, or in green or brown bottles, in order to prevent light from being transmitted through the glass. 21 Cont’d….. • Acetaldehyde : fermentation: is produced as a precursor to ethanol produced during • it is formed when there is Yeast strain (highly flocculent strains), Poor yeast health, Fermentation at temperature too cool for yeast, Incomplete/stuck fermentation, Removing yeast from wort prematurely (e.g., fining, filtering, crash cold conditioning), Insufficient conditioning time, Aeration of green beer, and Bacterial infection. • To Avoid or Control:  Proper fermentation temperature,  Longer fermentation and/or conditioning times,  Proper yeast health/quality,  Proper yeast strain &  Proper sanitation (to avoid bacterial infection). 22 Vicinal Diketones (VDK)  Vicinal diketones (VDK) consist of diacetyl & pentanedione. Since they are virtually indistinguishable by typical chemical tests, they are grouped together.  Both are natural byproduct of fermentation. The highest concentrations are found in the initial stages of fermentation, during they reabsorbed by yeast in final phases of fermentation and are metabolized to relatively flavorless substances.  VDK are however more acceptable, and even wanted in ale styles, where their sweetness helps to balance some of the bitter and harsh hop flavours. 23 Diacetyls  Has intense buttery aroma, produced during fermentation as a byproduct of valine synthesis when yeast produces α-acetolactate, which escapes the cell and is spontaneously decarboxylated into diacetyl.  The yeast then absorbs the diacetyl, and reduces the ketone groups to form acetoin and 2,3-butanediol. 24 Cont’d…. • Pentanedione: is produced during fermentation as a byproduct of isoleucine synthesis when yeast produces α-ketobutyrate, which escapes the cell and is spontaneously decarboxylated into 2,3- pentanedione. The yeast then absorbs the 2,3- pentanedione and reduces the ketone groups to form relatively flavorless compounds. Increased By: Yeast strain selection - some produce more VDKs, especially those which flocculate well and those which produce respiratory-deficient mutants, - Wild yeast infection (bacterial contamination can produce high levels of 2,3pentanedione). - Insufficient or excessive yeast growth, Yeast mutation, Reusing yeast collected too early in previous fermentation cycle. 25 Caramelization • Caramelization occurs when sugars are heated over their melting points. • When heated by dry heat, granulated sugar will melt @ approx. 160oC with continued heating the melted sugar will gradually turn brown to form caramelized sugar. • The extreme heat pulls water out of the sugar molecule to form furfural derivatives that undergoes a series of reactions that are polymerized to brown coloured compounds. Beer color 27 Quality Control in Beer Production Setting up specifications is done. Brewers decide on the basic properties of original gravity, color, and flavor and from this develop a formulation of raw materials. 1) Sensory methods: are not necessarily easy to apply but are useful and quite cheap to do. They include an analysis of beer flavor, beer clarity, color, and foam.  Beer color can be measured in a comparator by quite cheap instruments, such as a tintometer.  A standard beer set aside for color matching remains stable for quite a long time if kept cold and in the dark.  Putting numerical values from instruments on flavor, haze, foam, color, and so forth. 28 Cont’d… Instrumental Analysis: These are original gravity (OG) and the degree of fermentability (alcohol content) of beers. These are most easily determined on wort by using a hydrometer and measuring cylinder. The degree of fermentability can be determined by a rapid fermentation test in which a high population of yeast cells, with frequent agitation, rapidly ferments out the wort. At the same time, wort flavor and clarity can be noted. 29 Cont’d…. Package beer, on the other hand, must be analyzed for CO2 content (carbonation) and bottle "air" for flavor stability. The microbiological test is to pass at least 100 ml of beer through a 0.45 micrometer membrane, then plate the membrane on media under conditions (for instance anaerobic at about 25° C) capable of detecting the target organisms in low numbers. 30 Beer Brewing Flow diagram Wort Boiler solids are Removed by settling at the bottom a vessel used for the extracted wort separation yeast metabolizes sugars and amino acids, and converts them into alcohol 31 32