The main material change in the process of mashing - the decomposition of starch
During the mashing process, important substances are decomposed: starch decomposition, protein decomposition, and glucan decomposition. The decomposition of these substances mainly
depends on the action of enzymes, and the decisive factors for the action of enzymes are temperature and pH value.
The decomposition of starch is the most important enzymatic reaction in the mashing process, and its main influencing factors are (temperature, time, pH value, mash concentration and stabilizer
calcium ion). Starch is the most useful ingredient in beer brewing and must be broken down thoroughly. Its decomposition products are maltose, dextrin and other intermediate products. Whether
the starch is completely decomposed not only directly affects the cost of beer production, but also affects the quality of beer (undecomposable residual starch will cause beer turbidity).
The decomposition of starch can be divided into three consecutive irreversible processes: gelatinization, liquefaction and mashing.
1. Gelatinization
Starch in malt and auxiliary materials is generally surrounded by cell walls and exists in granular form. The granules are insoluble in water and are not affected by amylases. However, when starch
granules are heated, they will quickly absorb water and swell. When the temperature rises to a certain temperature, the cell wall will rupture, and the starch molecules will be dissolved to form a
viscous paste. This process is called "gelatinization". The process of expansion and rupture in hot solution.
After the starch is gelatinized, the amylase in the mash can decompose it well, but the decomposition of ungelatinized starch takes many days.
The gelatinization temperature of different grains is different, which is caused by the different sizes and chemical compositions of starch granules in different grains. For example: general malt starch
and barley starch can be gelatinized at 60°C in the presence of enzymes; the gelatinization temperature of rice starch is 80°C~85°C; the gelatinization temperature of wheat starch is 57°C~70°C; The
gelatinization temperature of sorghum starch is 68°C~78°C; the gelatinization temperature of sorghum starch is 68°C~78°C. If a-amylase is added during the gelatinization process, the gelatinization
temperature will be greatly reduced.
2. Liquefaction
α-amylase quickly decomposes the long chains of starch (amylose and amylopectin) composed of glucose residues into short chains to form low-molecular dextrins, thereby rapidly reducing the
viscosity of the gelatinized mash and forming a thin mash , This process is called "liquefaction", and the liquefaction process is a biochemical reaction process. The meaning of liquefaction is to
reduce the viscosity of gelatinized starch liquid through the action of α-amylase. Of course, β-amylase will also work during the liquefaction process, decomposing the long chain from the
non-reducing end, but its action is slow and the decomposition time is long.
3. Mashing
Mashing refers to the process in which amylase converts starch into sugars such as maltose, maltotriose, glucose, and dextrin, and is a biochemical reaction process.
The decomposition of starch by amylase can be summarized as follows:
(1) α-amylase decomposes long-chain starch into low-molecular-weight dextrin, and its optimum action temperature is 72°C~75°C.
The active temperature is 80℃, and the optimum pH value is 5.6~5.8.
(2) β-amylase decomposes from the end of the starch chain to form maltose, maltotriose and glucose, and its optimum action temperature
The temperature is 60°C~65°C, the inactivation temperature is 70°C, and the optimum pH value is 5.4~5.5
4. Composition of extract in wort
During the mashing process, the following starch decomposition products are mainly produced:
(1) Glucose: first decomposed by yeast (from fermentable sugar).
(2) Maltose and other disaccharides: can be fermented well and quickly by yeast (main fermentable sugar)
(3) Maltotriose: It can be fermented by all high-fermentation yeasts. Maltotriose (post-fermentative sugar) can be decomposed only after the fermentation of maltose is completed, that is, in the
post-fermentation storage stage.
(4) Dextrin: It is not fermentable and is the main component of residual sugar in beer.
5. Factors Affecting Starch Decomposition
(1) Malt variety and quality.
(2) Grinding degree.
(3) Mashing temperature.
(4) Mashing time.
(5) The pH value of the mash.
(6) Mash concentration.
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