mashing is the process of mixing water with milled cereal grains to extract their starch and convert it into sugars assimilable by the chosen yeast strain to produce alcohol. The starch contained within the cereal grain endosperm becomes solubilized when the mash achieves the appropriate temperature to gelatinize it. Then, amylolytic enzymes, either contained within the malted barley (endogenous) or from exogenous sources, convert it into smaller fermentable carbohydrates. Each enzyme has an optimal temperature and pH range; however, 62–65° C and 5.4–5.6, respectively, is an ideal profile for targeting the three major amylolytic endogenous enzymes:
The water is added at a temperature that varies according to the type of mashing. Scotch distillers, for instance, will add water at about 63° C to the mash; bourbon distillers will add rye or wheat to their cooked corn at around 77° C and slowly drop the temperature to 63° C before adding the malt. For distillers, the aim is to extract and convert all of the starch into fermentable carbohydrates to maximize the ethanol yield. This is contrary to mashing for beer production, where the aim is to balance fermentable carbohydrate and unfermentable dextrin, as these compounds contribute to mouthfeel and the overall sensory experience. However, with the production of distilled spirits, dextrin (residual extract) is not only a loss of ethanol and profit but can contribute to downstream processing issues as well. Mashing protocols are largely determined by cereal grain used, equipment (hammer mill vs. roller mill, mash mixer vs. jet cooker), and the country of production (Scotland vs. United States). See mash. A wide variety of cereals are used in modern distilling; however, corn, rye, wheat, and malted barley are the most common. Each grain has a slightly different gelatinization point and this is due largely to the type and ratio of starch molecules, amylose vs. amylopectin, and the size of starch granules in the grain’s endosperm. In general, smaller or more tightly compacted granules require a higher gelatinization point, as is the case with corn. Aside from starch solubilization and composition, other constituents of cereals, such as proteins, β-glucans, and pentosans, also impact mashing. Rye and wheat have higher protein and pentosan levels than corn, which significantly impacts starch concentration and availability. This is largely due to the structure of the endosperm. The plant cells of the endosperm are enclosed within an inner and outer cell wall composed of β-glucans and pentosans; and within the cell, the starch molecules are dispersed within a proteinaceous matrix. In order to access the starch contained within the endosperm for subsequent hydration and conversion, the cell wall structure and intercellular matrix must be degraded. Since rye and wheat have higher protein and lower starch levels than corn, yields are lower, and substantial proteolysis must occur for maximum extract to be achieved. This is not the case with malted barley, as the malting process has already degraded the cell walls and intracellular protein matrix, thus making the starch readily available for conversion to fermentable carbohydrates during mashing. Regulations in the country of production can impact the raw materials and processing used. For example, Scotch whisky regulations stipulate that only endogenous enzymes may be used during mashing, and this dictates the mash bill. Meeting this requirement necessitates a greater inclusion of malt with high diastatic power in addition to any other grains used. American whisky has no such stipulations on enzyme origin, and the use of exogenous enzymes (α-amylase, pullulanase, and α-glucosidase) is commonplace. This correlates to a much lower percentage of malted barley within the mash bill and less conservative time and temperature restrictions, as exogenous enzymes generally are more thermostable and more efficient. In addition to the conversion of starch into fermentable sugars, the extraction and/or generation of necessary nutrients for the chosen yeast strain is critical to a successful fermentation; these nutrients include free amino nitrogen, B-vitamins, zinc, and many others. There is also the generation/release of materials that will eventually contribute to the flavor profile of the spirit, such as ferulic acid. Rye whisky is known for a quintessentially spicy character, which comes from the conversion of ferulic acid into 4-vinyl guaiacol, a clove-like aroma, by the yeast; therefore release of ferulic acid from the grain is a desired step during mashing. Briggs, D. E., J. S. Hough, R. Stevens, and T. W. Young. “Adjuncts, Sugars, Wort Syrups, and Industrial Enzymes.” In Malting and Brewing Science, vol. 1, Malt and Sweet Wort, 2nd ed., 222–253. Kluwer Academic / Plenum, 1981. Briggs, D. E., J. S. Hough, R. Stevens, and T. W. Young. “The Chemistry and Biochemistry of Mashing.” In Malting and Brewing Science, vol. 1, Malt and Sweet Wort, 2nd ed., 254–303. Kluwer Academic / Plenum, 1981. Dolan, Timothy C. S. “Malt Whiskies: Raw Materials and Processing.” In Whisky Technology, Production, and Marketing, ed. Inge Russell, Charlie Bamforth, and Graham Stewart, 68–70. San Diego: Elsevier, 2003. By: Elizabeth Rhoades
