Mashing is the biochemical process where starches are converted to sugars. Starches are long chains of sugar (glucose) molecules connected by ether linkages. An ether linkage is where two sugar molecules join together and one water molecule is removed.
In mashing, enzymes cause water molecules to be reintroduced to the ether linkages, thereby breaking them and freeing the individual sugars from the chains. This process of breaking the ether linkages is called hydrolysis.
The term "starch" refers to a family of molecules, all of which are chains of sugars. Some starches are chains of as many as 400 sugar molecules, and others are chains of as few as four sugar molecules. Shorter-chain starches are soluble in water. Longer-chain starches are insoluble in water.
The mashing process is comprised of two phases: liquefaction; and, saccharification. The liquefaction phase involves the action of alpha-amylase enzymes reducing the longer-chain insoluble starches to shorter-chain soluble starches. Hence, "liquifying". The second phase, saccharification, involves the action of beta-amylase enzymes reducing the shorter-chain soluble starches to sugar molecules.
In the production of grain liquors, the starches are supplied by the grains being mashed (e.g. corn, rye, millet, wheat, etc.). Grains are, for the most part, made up of starch, protein, and fiber. Although, different grains are comprised of slightly different proportions of starch, protein, and fiber, they are all roughly 50% starch. And, mashing acts on that 50% starch.
Malted grains (e.g. corn malt, rye malt, barley malt) supply the enzymes used for the production of grain liquors. Barley malt is by far the most widely used, and is the choice in this text. There are laboratory enzyme preparations available for mashing, but they are most commonly used in very large-scale alcohol production. These laboratory enzymes will not be discussed here, with the exception of gluco-amylase, discussed in the chapter on Ingredients.
For malt enzymes to work properly, there are certain optimum conditions that are important to observe. These conditions are as follows.
Mash Water: The water used must be very nearly devoid of iron. A high iron content will denature (i.e. destroy) the enzymes. However, a fairly high calcium content (50-250 ppm) is beneficial to the subsequent fermentation and the resulting flavour of the finished whiskey.
Sulphates are preferable to carbonates and bicarbonates, but all are acceptable in the process.
If suitable source water is not available, you can use deionized or distilled water. The addition of 10-ml (2-tsp) of gypsum (calcium sulphate, CaSO4) per 20L is beneficial if using pure water.
pH: Unless you have an accurate pH meter, it's very difficult to measure the pH of the mash after the grain has been added. Most people use pH papers and, for all practical purposes, pH papers can only be used to measure the pH of the mash water before the grain is added.
Because the addition of the grain to the mash water will cause the pH of the mash water to go down slightly, combined with the fact that the conversion process itself results in a slight lowering of pH, it is best to establish a mash-water pH on the high side of optimum, say 5.8 or 6.0.
Measuring pH: To measure the pH of the mash water, thoroughly rinse a clean shot glass in the water to be measured. Draw off a small sample of the water in the shot glass, say 2-ml. Cut a 11 cm (3/4") strip of pH paper (of whichever range is required), and place it in the 2 ml sample.
Allow the pH paper to steep in the water sample for a few minutes to enable the indicator to mix with the water and change colour. Hold the shot glass up to the light and compare the colour with the colour table on the pH-paper packaging and determine the pH of the water.
Adjusting pH: A pH of 5.8 to 6.0 should be established for the mash water.
It is very rare that the pH of the source water is too low and requires adjusting upward. However, if this is necessary, calcium carbonate (CaCO3), aka precipitated chalk, should be used to raise the pH. CaCO3 should be used in comparatively small additions since a relatively small amount will raise the pH a surprisingly large amount.
As is the condition with most source waters, the pH will likely need to be reduced. Since sulphates are notionally more beneficial to mashing than other radicals, 95% sulphuric acid (H2SO4) should be used one drop at a time to lower the pH. As a general guideline, 20L of source water at pH 8.5 would take about 11 drops of 95% H2SO4 to reduce the pH to 5.8.
Warning: See 95% sulphuric acid in the chapter on Ingredients for important information about safety and alternatives for sulphuric acid.
In order to avoid overshooting the target pH, it's useful to add the CaCO3 or H2SO4 in small incremental additions, taking measurements after each addition until the target pH is achieved.
Temperature: The optimum temperature range for alpha-amylase enzymes (liquefying enzymes) is from 67oC to 71oC (152oF to 160oF). The optimum temperature range for beta-amylase enzymes (saccharifying enzymes) is from 60oC to 66oC (140oF to 151oF).
Since a temperature that favours alpha-amylase activity, 67-71oC (152-160°F), tends to produce a mash with a high proportion of unfermentable sugars (i.e. dextrins and polysaccharides), and tends to denature beta-amylase enzymes; it is best to hold to temperatures in the range that favours beta-amylase activity, 60oC-66oC (140-151oF). The alpha-amylase will work at the lower temperatures, just not as fast as it would in its optimum range.
If the mashing apparatus, or the mashing quantity, is capable of holding a single temperature constantly for 60 to 90 minutes then 63oC (145oF) is the optimum conversion temperature. In fact, many commercial whiskey distilleries use 63oC (145oF) as their conversion temperature.
On the other hand, if one is using a more rudimentary mashing apparatus, such as a large pot on a kitchen stove, then it is better to establish a conversion temperature of 65.5oC (150oF). During the 60 to 90 minute conversion rest, the temperature will slowly cool to about 60oC (140oF), thereby keeping the temperature within the optimum range throughout the conversion cycle.
It's important to note, that a mash at 71oC (160oF) or higher will rapidly denature the enzymes and may result in an incomplete conversion. Also, a large proportion of the resulting sugars would be unfermentable. And as a final note, a mash temperature of 75.5oC (168oF) or higher will instantly denature the enzymes. In fact, heating a mash to 75.5oC (168oF) after conversion is complete, is regularly done in the commercial brewing industry to "mash out" or halt all enzyme activity.
Iodine Starch Test: After the 90-minute (or longer) conversion rest, the starches will be completely converted to sugars. This can be tested for by means of an iodine starch test.
After the conversion rest, there will be a clear light yellow liquid about 7 or 8 cm (3") deep on top of the mash. Using the floating thermometer, carefully dab a few drops of this clear yellow liquid on a white porcelain saucer or plate, taking care to avoid getting any of the mash solids suspended below the clear liquid in the sample.
Dab a drop or two of tincture of iodine into the sample on the porcelain saucer or plate. If there is any starch at all in the sample, the sample will turn an inky blue as soon as the iodine contacts it. If there is no starch, the sample will stay more or less the colour of the iodine.
You may observe tiny granular dots of blue in the sample when the iodine is added. This is not an indication of starch, but a result of cellulose from tiny particles of mash solids suspended in the sample. Iodine turns a dark blue, almost black, in the presence of cellulose in water. This is why you should take care to avoid getting the mash solids in the sample. Anyway, this cellulose indication can be ignored, and you can conclude there are no residual starches in the mash.
When the iodine starch test is complete discard the sample. Do not attempt to return it to the mash.
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