The characteristic of decoction mashing

The basic operation of decoction mashing is to take out a part of the mash and boil it, then pour it back into the main mash tank to maintain a constant mash temperature. There are two purposes for boiling part of the mash:

• Use physical methods to destroy the cell wall of starch cells in malt. Boiling the grain helps break down the cell walls and make the starch more accessible to amylase, which is especially important for low-modified malt.

• After the two parts of the mash are mixed, the temperature of the wort is increased to the desired higher temperature.

The form and quantity of the boiled mash is of great significance to the mashing and decomposition process: if the stirring is stopped, the undissolved part of the mash will sink to the bottom of the mashing tank, called thick mash.And the dissolved mash will be in the upper part of the mashing tank, called thin mash. Since the thick mash still contains starch granules, the thick mash must be boiled. While the thin mash is rich in enzymes, so boiling is not allowed. The boiling process will kill all enzymes in the mash, so the enzymes in the unboiled mash are needed to decompose starch. When mixing the boiling mash with the remaining mash in the mashing tank, the stirrer must be activated in order to protect the enzyme. The amount of boiling mash determines the desired temperature after the mash, which can be divided into mash based on experience, generally 1/4-1/3 of the total mash.

In the actual operation process, there have been different operation methods, which are divided into three step decoction mashing, two steps decoction mashing and one step decoction mashing according to the number of boiling. The most typical is the three-step decoction, which was once a commonly used method. Although this method is time-consuming and labor-intensive at present, it is no longer popular, but it is the basis for understanding the principles behind all the decoction mashing.

The starting temperature of the three-step decoction is 35-37℃, and the ratio of malt to water is 1:3. Three-step decoction mashing mainly has three temperature stops: acid stop, protein stop and saccharification stop. Pause the stirring and wait a few minutes at each stop. The main part of the mash containing grains is pumped into the cooking tank and heated and boiled. During the heating process, it can be stopped at 62°C-65°C or 72°C. The boiling time is 30 to 45 minutes, while the thin mash is kept at a constant temperature of 35°C–38°C. After mixing the two parts of the mash, the temperature of the mash will rise to the protein resting temperature of 50°C–55°C.

The second step is similar to the first step: separating, heating and boiling the thick mash while keeping the thin mash at the optimum temperature for enzyme action. After the second boiling and mixing of the mash, the resting temperature (62 °C-65 °C) for starch breakdown (starch into sugar) is reached. Then the stirring stopped for 10 minutes, separated again and started to cook. Different from the previous steps, the third step of the traditional three-step decoction mashing is to boil the thin mash. This process seems somewhat illogical, and it also violates the basic concept of decoction mashing, because most amylases are in the thin mash and lose their activity during the boiling process. Interestingly, this method is to keep the degree of fermentation at a low level, so as to brew a thick and sweet beer.

The mashing temperature after the third boiling and mixing of the mash is 75°C, and it takes about 15 minutes for the mash to stop. Therefore, the duration of the three-step decoction mashing is very long. When using dark malt, it takes about 5.5 hours, while light malt takes about 3.5 to 4 hours.

For dark malt with poor enzyme activity, it is reasonable to use the three-step decoction mashing. However, this method may damage the malt flavor and foam stability when using the modified light-colored malt processed by modern malting technology.

In order to avoid energy waste and deterioration of beer quality, the two-step decoction mashing is an alternative feasible method. The classic two-step decoction mashing can be regarded as a shortened three-step decoction mashing . The first acid stop is omitted, it starts with the protein stop at 45°C–50°C. The following steps are similar to the previous three-step decoction mashing . Both decoction mashing use thick mash to physically gelatinize and destroy the starch cell wall to increase enzyme activity. The thin mash part is kept at a constant temperature to make full use of the enzyme activity. The change of the two-step decoction mashing is based on the different mashing temperature and the rest of the heating process. Beer produced by the two-step decoction mashing , if the process matches the malt used, will have a particularly strong flavor and often exhibit very good foam stability.

Finally, the single-step decoction mashing is also a combination of the decoction mashing and the infusion mashing to achieve the required resting temperature. There are many ways to achieve this. Before separating the mash, the standard temperature process can be used for mashing to reach the amylase resting state at 65°C. The mash can be separated at the start temperature of mashing, and then follow the steps until it boils. The beer brewed by the saccharification method is softer, fresher, and brighter in color.

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