P1: SFK/UKS BLBS102-c33 P2: SFK BLBS102-Simpson March 21, 2012 14:5 Trim: 276mm X 219mm 628 Printer Name: Yet to Come Part 5: Fruits, Vegetables, and Cereals fermentation needs to be performed During this fermentation, major flavor-active compounds are produced (and some of them are again metabolized) by the yeast cells The metabolism of the most important fermentation by-products during main and secondary fermentation is discussed in detail The latest trend in beer fermentation technology is the process intensification using immobilized cell technology (ICT) This new technology is explained and some illustrative applications—on small and large scale—are discussed THE BEER BREWING PROCESS The principal raw materials used to brew beer are water, malted barley, hops and yeast The brewing process involves extracting and breaking down the carbohydrate from the malted barley to make a sugar solution (called “wort”), which also contains essential nutrients for yeast growth, and using this as a source of nutrients for “anaerobic” yeast growth During yeast fermentation, simple sugars are consumed, releasing heat and producing ethanol and other flavoring metabolic by-products The major biological changes, which occur in the brewing process, are catalyzed by naturally produced enzymes from barley (during malting) and yeast The rest of the brewing process largely involves heat exchange, separation, and clarification, which only produces minor changes in chemical composition when compared to the enzyme catalyzed reactions Barley is able to produce all the enzymes that are needed to degrade starch, β-glucan, pentosans, lipids, and proteins, which are the major compounds of interest to the brewer An overview of the brewing process is shown in Figure 33.1, where also the input and output flows are indicated Table 33.1 gives a more detailed explanation of each step in the process CARBOHYDRATE METABOLISM—ETHANOL PRODUCTION Wort Carbohydrates Uptake and Metabolism Carbohydrates in wort make up 90–92% of wort solids Wort from barley malt contains the fermentable sugars sucrose, fructose, glucose, maltose, and maltotriose together with some Malt Brewing water Unmalted cereals Hops/hopproducts Milling Mashing Wort separation Spent grains Syrups Wort boiling Wort clarification Wort cooling and aeration Hot trub Spent hops Yeast Primary fermentation Yeast Maturation and conditioning Beer filtration Beer stabilization Cold trub Yeast Beer packaging Figure 33.1 Schematic overview of the brewing process (input flows are indicated on the left side and output flows on the right side) P1: SFK/UKS BLBS102-c33 P2: SFK BLBS102-Simpson March 21, 2012 14:5 Trim: 276mm X 219mm Printer Name: Yet to Come 629 33 Biochemistry of Beer Fermentation Table 33.1 Overview of the Brewing Processing Steps: From Barley to Beer Process Action Malting Steeping Germination Kilning Moistening and aeration of barley Barley germination Kilning of the green malt Milling Grain crushing without disintegrating the husks Addition of warm/hot water Mashing + wort separation Wort boiling Boiling of wort and hops Wort clarification Sedimentation or centrifugation Wort cooling and aeration Fermentation Use of heat exchanger, injection of air bubbles Adding yeast, controlling the specific gravity, removal of yeast Maturation and conditioning Beer storage in oxygen free tank, beer cooling, adding processing aids Beer clarification Biological stabilization Packaging Centrifugation, filtration Pasteurization of sterile filtration Filling of bottles, cans, casks, and kegs; pasteurization of small volumes in packings Objectives Preparation for the germination process Enzyme production, chemical structure modification Ending of germination and modification, production of flavoring and coloring substances Enzyme release and increase of surface area Stimulation of enzyme action, extraction and dissolution of compounds, wort filtration, to obtain the desired fermentable extract as quick as possible Extraction and isomerization of hop components, hot break formation, wort sterilization, enzyme inactivation, formation of reducing, aromatic and coloring compounds, removal of undesired volatile aroma compounds, wort acidification, evaporation of water Removal of spent hops, clarification (whirlpool, centrifuge, settling tank) Preparing the wort for yeast growth Production of green beer, to obtain yeast for subsequent fermentations, carbon dioxide recovery Beer maturation, adjustment of the taste, adjustment of CO2 content, sedimentation of yeast and cold trub, beer stabilization Removal of yeast and cold trub Killing or removing of microorganisms Production of packaged beer according to specifications dextrin material (Table 33.2) The fermentable sugars typically make up 70–80% of the total carbohydrate (MacWilliam 1968) The three major fermentable sugars are glucose, α-glucosides maltose, and maltotriose Maltose is by far the most abundant of these sugars, typically accounting for 50–70% of the total Time Temperature (◦ C) 48 h 3–5 d 24–48 h 12–22 22 22–110 1–2 h 22 1–2 h 30–72 0.5–1.5 h >98