Process Variables Affecting Mashing
The critical process variables during mashing that determine wort quality are temperature, mashing time, pH, water, and mash thickness.
As mentioned, the temperature influences the amount of extract produced (yield) and the fermentability of the wort during mashing. In general, the higher the temperature, the greater the yield but the lower the fermentability of the wort. At lower temperatures less extract is produced, but fermentability is higher. In terms of final beer quality, reduced fermentability means a reduced alcoholic strength. Only at very high temperatures will extract begin to drop off.
Mashing in, the initial mix of grist and water (i.e., liquor), is a critical process point for any regime, but more so for the infusion system.
The temperature used for mashing is a function of malt modification. This is because the extent of modification influences the rate of starch solution. Lower temperatures are needed for well-modified malts because most of the enzymes are destroyed in the kiln, particularly beta-amylase, which is necessary for starch conversion. If the temperature is too high, starch conversion may not go to completion, resulting in low extract and possible starch haze in the finished beer.
Regarding time and temperature, the mash will be held at a temperature for a specified period called a step or rest. The mashing process can involve several temperature rests depending on what process the brewer wishes to accomplish (create more sugars, reduce the amount of proteins, etc.).
Sparging occurs in the lautering process, which describes the separation of the wort and the spent grain in the mash (Chapter 9, Wort Separation).
Mash times are another factor influencing yield and the fermentability of the wort. In general, longer mash times increase the concentration of the extract, but the rate of increase becomes slower (Kunze, 1996).
The nature of the mashing water has an important influence on mash reactions. The ions of major importance at mashing are those of calcium, carbonate, and bicarbonates (Comrie, 1967). Calcium lowers the pH of the mash mainly by its interaction with phosphates and to a lesser degree with protein from the malt. In addition to the advantages achieved by favorable pH adjustments the calcium ions stabilize alpha-amylase during mashing, accelerate wort separation and run-off from the mash, assist in break formation in the hop-boil, and the beer clarifies better.
pH Control during Mashing
It is important to control the pH during mashing. The grist composition will be a key controlling parameter; the primary proportions of malt to adjunct, the malt protein content, the degree of malt modification, kilning characteristics, etc., will all be major determining factors of wort composition. However, the water composition (possibly after treatment) used for mashing and sparging can have significant impact too.
The pH should be measured and periodically adjusted, if necessary, throughout the mash process. The pH observed for the mash will vary greatly with temperature. This is an important consideration if using a pH meter without temperature compensation. A hot mash will read at a lower pH than a mash cooled to room temperature due to the variation in ion activity.
Acidification of Mash
To lower the pH of the mash it can be corrected by the addition of highly kilned malts, salts, or acids, or by biological acidification.
Mashing performance is significantly affected by mash thickness. A low liquor-to-grist ratio mash retains beta-amylase activity, resulting in higher wort fermentability. Thin mashes (i.e., its ratio of grist to brewing water) favor the conversion of starch to sugars, while in thick mashes the rate of saccharification is retarded, probably because the accumulating sugars competitively inhibit the hydrolytic enzymes (Dougherty, 1977).
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