Brewing enzymes as defined by Gregory J. Noonan in his book
Brewing Lager Beer,
"are complex, protein-based biological catalysts that induce reactions between substances without being changed by the reaction or appearing in its end product." They are activated and deactivated under certain conditions. Manipulating these conditions is what mashing is all about.
Brewing enzymes we as homebrewers use when making our beer are created inside the grains during the malting process. The maltster tricks the barley grain into thinking it is about to sprout by wetting it and initiating germination. Inside the barley grain, mother nature has a multitude of enzymes ready to help the young sprout develop. The enzymes we are interested in are the ones that break down the starch inside each kernel and allow the sprouting grain to use the resulting sugar as food until it can reach the surface and develop leaves to photosynthesize the sun's energy into its own food. The enzymes developed in the germination and drying process can be used by the brewer to convert the cracked malted barley into a sweet liquid during the mashing process. The sweet liquid is separated from the grain and rinsed of all available sugar during the sparging process. This sweet liquid, now in the brewer's kettle, is then boiled with hops to finish the process of making wort. After being cooled, this sweet wort is pitched with yeast and after the fermentation process is complete, beer is produced.
This is a simplified version of what goes on prior and during the brewing of beer. The beer enzymes homebrewers are concerned about are the ones that we can control. These are the proteases or proteolytic enzymes, which as the name implies, break down proteins. The other brewing enzyme we can control is called diastase or the diastatic enzymes which break down starches.
Protein molecules are long complex organic chains containing nitrogen. They are made of amino acids strung together to form coiled chains with thousands of atoms. The proteolytic malt enzymes break these long chains down into a form that we use to improve our beer. Proteins are important to us because after they are broken down by proteolytic enzymes, the resulting amino acids and other products are used as nutrients by the yeast. Some protein remains in the finished beer giving it richness and mouthfeel. The proteins are also responsible for the beer's head retention. It is the nitrogen in proteins that combine with carbohydrates during kilning to produce many of the flavors we enjoy.
Proteolytic Enzymes: Two groups of proteolytic enzymes are important in the brewing process, proteinase (protease) and peptidase. Proteinase breaks down the very large protein molecules into smaller amino acid chains, which enhances the head retention of beer and reduces haze. The other enzyme is peptidase. It breaks down the smaller amino acid chains released by proteinase, but only works from the ends, releasing nutrients used by the yeast. The process of activating the proteolytic enzymes is called the protein rest. Most proteins in the wort are not soluble until the wort reaches the 113°-131° range of the protein rest. The two enzyme's temperature ranges overlap, but the ideal temperature for a protein rest is 122°F (50°C). The enzymes are denatured by temperatures greater than 150° F (65°C). Its ideal pH range is a little below the normal mash pH of 5.2-5.8, but it works well enough at this range that you shouldn't worry about lowering the mash pH to accommodate them. The protein rest isn't as important as it once was because most malts are fully modified. The longer malting time allows proteolytic enzymes to break down proteins in the malt to a certain degree, and the protein rest is not used much anymore. If you like to drink your lighter ales well chilled, or use an undermodified malt, or use a large proportion of unmalted or flaked grains (usually >25%), then you may want to use a protein rest in your mash schedule. Using the rest with fully modified malts could result in the proteins responsible for head retention and mouthfeel being broken down yielding a thin watery beer.
There are other proteolytic enzymes working in this temperature range called the beta-glucanases. These malt enzymes break down the beta-glucans present in the bran of cereal grains. Beta-glucans occur most commonly as cellulose in many plants and elsewhere. For brewers they can cause problems by making the wort too viscous and gummy if not broken down. When incorporating more than 25% unmalted grains into the grist, brewers can use a rest between 98° and 113°F (37°-45°C) which is below the protein rest, for 20 minutes to break down the gums without affecting the proteins which help head retention and mouthfeel.
Diastatic enzymes: The diastatic brewing enzymes break down and convert starch (the endosperm of the grain) into fermentable sugars and unfermentable dextrins. We are interested in the two diastatic enzymes that become active during the mash. These are alpha-amylase and beta-amylase. They work together to break down long complex chains of soluble (or gelatinized) starch molecules into sugars or dextrins. Starch molecules are basically just long chains of glucose molecules. But due to the bonds between them, they are not fermentable. Maltose has two glucose molecules bonded together and is fermentable. Dextrins have long chains with four or more glucose molecules and are byproducts of starch conversion. Dextrins are not fermentable and have no taste. They do however add body and mouthfeel to beer.
Alpha-amylase chops up starch molecules randomly into chunks that beta-amylase can then work on. Until these molecules are chopped up, they are unfermentable and called dextrins. What alpha-amylase does is called liquefication. It physically liquefies the starches, making them ready for further enzymatic activity. Mash schedules that target the alpha-amylase enzymatic action (optimum at 158°F/50°C) yield a wort with a high percentage of unfermentable sugars, or dextrins. The beer produced is very rich, with a thicker body and mouthfeel.
Beta-amylase breaks down starch and dextrins into glucose (one molecule), maltose (two molecules) and maltotriose (three molecules). After beta-amylase is through working, the starch has been broken down into fermentable sugar. Mash schedules that target the beta-amylase enzymatic action (optimum at 140°-149°F/60°-65°C) yield a wort that is highly fermentable. The beer produced will be drier tasting and contain more alcohol.
It is important to understand that although mash enzymes have an optimum temperature, they will work over a wide range, and most of the time, the activity of enzymes overlap within that range. Both alpha-amylase and beta-amylase will work well together within the range of 145° to 158°F (63°-70°C). So in general, if you want a thinner, drier, more alcoholic beer you can rest your mash in the lower portion of this range, and if you want a richer more dextrinous beer with more mouthfeel and body, you should rest your mash in the upper portion of this range. A good compromise is made by mashing in the middle, around 152°F (67°C).
For more information on wort production,
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