The mash mixer is again a steam-jacketed, stainless steel vessel located above the lauter tun, adjacent to the cereal cooker. It is fitted with baffles, and a two speed agitator. The low speed setting is used during "rest" periods, while the high speed setting is used during "mash-in" to mix the malt and the brewing water, and during any phase in which steam is applied to the vessel.
When starting a brew, usually half of the brewing water is mashed in with the adjuncts and the grist. The remainder of the treated water is reserved at a higher temperature to be used in the sparging process which will follow later.
In the mash mixer, we subject the mash to ascending temperatures for varying periods of time. During these temperature and time intervals, the starch of the malt is being converted to simple sugars such as maltriose and maltose, while dextrins and complex proteins are being broken down to peptides and amino acids.
The brewmaster consequently has very close control of the product during the mashing process. Generally, we mash in at a temperature near 48 degrees C (118 degrees F). In the temperature range from 48 to 54 degrees C (118 to 130 degrees F), proteolytic enzymes break down the proteins to simple peptides and eventually amino acids. The resulting protein derivatives in wort fall into two main classes:
1. Simple compounds, mainly amino acids assimilable by yeast.2. Complex compounds, not assimilable by yeast, which remain in beer to give head retention properties, fullness, and can be the cause of haze production.
The typical water soluble, coaguble protein of malt, the albumin, is extracted in the mash and a small proportion is degraded to permanently soluble substances, but the greater part is denatured and coagulated in the kettle during boiling.
After a predetermined rest period at 48 to 54 degrees C (118 to 130 degrees F) to facilitate proteolysis, we raise the temperature gradually from 60 to 68 degrees C (140 to 155 degrees F). Through this range of temperatures, enzymes which accomplish starch conversion to sugar are brought into play. Diastase, the enzyme complex responsible for these changes, is composed of alpha and beta amylase. This enzyme complex is capable of liquefying all the starch of the malt and also the starch of the corn that was added as adjunct. The optimum temperature range for the activity of beta amylase is some 10 degrees C (20 degrees F) lower than that of alpha amylase and it is destroyed more rapidly at higher temperatures. When we reach 65 degrees C (149 degrees F) alpha amylase is catalysing pretty well alone.
The nearer the temperature approaches the lowest permissible limit of 60 degrees C (140 degrees F) being gradually raised through 5 or 7 degrees C (10 or 14 degrees F), the greater the ratio of maltose to dextrins and conversely, the nearer it approaches 68 to 71 degrees C (155 to 160 degrees F), the greater the ratio of dextrins to maltose.
A wort rich in maltose will ferment freely, attenuation will be rapid and a thin beer will result. A wort rich in dextrins will attenuate slowly and a large proportion of the wort solids remain unchanged through fermentation and we produce a dextrinous beer, full drinking which, if aged properly, will produce a reasonable amount of "bite". After subjecting the mash to various temperature increases and timed rests to effect proteolysis and saccarification, we test a little of the wort solution with iodine to ensure that all the starch has been converted to sugars.
The gentlest form of transfer is by gravity. This minimises shearing and impact damage to the malt husks. After completion of the mash mixer procedures, the mash is dropped into the third vessel, the lauter tun, lautern meaning "to strain".
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