Chapter 9

Mashing

Decoction Mashing

Decoction mashing is the traditional method used in the production of wort for bottom-fermentation beers and is most commonly associated with the production of lagers in Germany. It was developed largely as a result of the use of under-modified or enzymatically weak malts. This system involves removing a portion of the mash (the decoction) for heating to conversion temperature in the mash kettle. After the decoction has undergone starch conversion, it is brought to a boil to inactivate the enzymes and returned to the main mash (i.e., mash mixer) to increase the overall temperature.

Three-Step Mash Decoction System

The three-step decoction involves acid, protein, and saccharification rests. The overall processing time is about 6 hours from mashing-in to lautering. There are many minor variations on the classical triple-decoction mash, especially with regard to the time in heating the decoction, the rate at which the decoction part of the mash is mixed with the main mash, and the length of the stands.

Mash-In

Mashing begins by mixing-in the malt and cold water in the mash mixer.

Acid Rest

After the mash-in stand, the temperature of the mash is raised to 35 to 40C to acidulate the mash (acid rest), which is done by the infusion of hot water or by direct heating.

First Decoction

Once the pH has dropped, about one-third of the mash (the decoction) is withdrawn, transferred to the mash kettle or otherwise known as the decoction vessel, and quickly heated within 10 minutes (or as rapidly as possible) to 65 to 70C.

Protein Rest

After the first decoction has been boiled in the mash kettle, it is then pumped back into the mash mixer, where it is continually stirred with the remaining thin rest mash.

Second Decoction

Following the protein rest, about one-third of the mash (the thickest part) is withdrawn for the second decoction and transferred to the mash kettle.

Saccharification Rest

After the second decoction has been boiled in the mash kettle, it is then pumped back into the mash mixer, where it is continually stirred with the remaining thin rest mash.

Third Decoction

When the starch endpoint has been verified, a very thin portion of the mash is removed for boiling in the mash kettle.

Mash-Off

Following boiling, the third decoction is pumped from the mash kettle back to the mash mixer where the temperature reaches 75 to 77C-the "mash-off" temperature.

Two-Step Mash Decoction System

The two-step decoction involves only protein and saccharification rests. The entire process usually takes 2 to 3 hours. As with the three-step decoctions system, there are many minor variations of the two-mash system, especially with regard to speeds of heating, the rate at which the decoction part of the mash is mixed with the main mash, and the lengths of the stands.

Single-Step Decoction System

The single-step decoction involves only a saccharification rest. The entire process usually takes fewer than 2 hours. As with the other decoction systems, there are many minor variations of the single-step mash system.

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