by Dave Sapsis
Barley is the most common source of the fermentable sugars in beer. The barley kernel is the seed of a plant of the grass family, Gramineae. Barley malt is formed by sprouting barley kernels to a desired length, then stripping off the rootlets and kilning (drying) the kernels to a specific color. These kernels consist of a germ, which is the actual germinating portion, and the endosperm, which is the starch or reserve food source for the germinating embryo. Both are surrounded by the husk, which is almost all cellulose. The acrospire is the portion of the developing plant that will become the above-ground shoot. Growing from the germ, the length of the acrospire has historically been used as an index of malt progress. As germination proceeds, enzymes acting on both proteins and carbohydrates are activated and transformed. The degree of germination is called modification; modification usually refers to the degree to which the protein/gum matrix of the endosperm has been broken down, and the degree to which proteins have become soluble in water.
A variety of measures can be used to indicate the degree of modification of malt. It is important to recognize that while the malting process is designed to initiate enzyme development that will be used to catalyze mashing reactions, the effects of varying malting regimes is dependent on barley strain. While undermodified malts usually have a more complete set of enzymes, they also have more proteins that require additional enzymatic breakdown to avoid protein-polyphenol induced haze (i.e., chill haze). The goal of the maltster is to accomplish the appropriate degree of protein degradation and starch availability, while not allowing too much carbohydrate substrate to be used up in plant development. Thought of another way, the maltster tries to manage desirable malt characteristics while still maximizing the potential yield from the barley.
It has become increasingly difficult to find truly undermodified malt that requires extensive protein rests as part of the mashing schedule. Measured both as a function of soluble Nitrogen (Kolbach Index) and as coarse:fine difference in extract, most modern malts have undergone a high level of protein degradation and most of the formerly bound starch is free in the friable endosperm. While there is no de facto assurance that malt will be suitable for brewing to a particular style, it is beneficial to understand modern barley growing and malting practices.
Two types of barley are commonly used in brewing. They are distinguished by the number of fertile flowers on the heads along the central stem. Two-row barley (Hordeum vulgare) has only two of the six flowers on the head fertile and able to produce kernels. Six row barley has all kernels fertile. An intermediate variety, called four-row, is in fact a six-row variety. It is not widely used in brewing due to the high protein content of the kernels.
Two-row barley will have bigger kernels, and thus higher yield than six-row. It usually has a lower nitrogen and protein content and also has a lower husk content, which makes 2-row beers taste less grainy. Six row barley, however, generally gives more yield per acre and has a higher diastatic power (more enzymes), so it is the choice whenever large amounts of adjuncts are used. The extra husk content of six-row also aids in providing a lautering filterbed.
The process of malting is done to convert the large, insoluble starch chains of the endosperm to water-soluble starches, and to activate both the proteolytic and diastatic enzymes that will reduce the proteins and starches into desirable components in the mash. The most important enzymes for malting are debranching enzymes, which break 1-6 links in a-glucans, and b-amylase, which produces maltose units by breaking 1-4 links near reducing ends. During the germination phase, the cell walls are broken down by the cytase enzyme complex, which includes hemicellulases and the b-glucanases. This clears a path for other enzymes into the endosperm so that degradation can proceed more easily.
Malting is basically sprouting the grains to a desired modification. The acrospire grows from the germ end of the corn to the opposite end. The ratio of the acrospire length to the length is the degree of modification, expressed as a percent or ratio. A ratio of 1.0 is indicative of fully-modified malt. Such a malt will be low in protein content and will have the endosperm almost fully converted to water-soluble gum. However, the starch content and potential yield will be reduced through its consumption during the growth of the acrospire and the rootlets.
American and Continental malts are generally less modified. Continental malt is modified only to 50-75%, which retains more of the endosperm for fermentability and creates greater nitrogen complexity, but at the price of reduced enzyme activity. American six-row is also modified to between 50-75%, but the higher protein and nitrogen content of six-row gives greater enzyme strength. Both Continental and American malts require a protein rest (at ~122 °F, 50 °C) to degrade the albuminous proteins into fractions that can be both used to promote yeast growth and give good head retention.
The barley is steeped in 50-65 °F (10-18 °C) water for about two or three days, then allowed to germinate for six to ten days between 50 and 70 °F (10 and 20 °C). The acrospire will usually grow to 50% at about the sixth day of germination. At the end of germination, the malt is gradually raised in temperature to 90 °F (30 °C), held there for 24 hours to permit enzyme action, and then gradually raised to 120 °F (50 °C). It is held at this temperature for 12 hours to dry the malt, as it is essential that the malt be bone-dry before being heated to kilning temperatures to prevent the destruction of the enzymes.
Kilning, or roasting the malt, combined with the degree of modification, determines the type and character of the grain. Vienna malts are low-kilned at around 145 °F (63 °C), British and American pale malts at between 130 and 180 °F (55 and 80 °C) and Czech malts are raised slowly from 120 to 170 °F (50 to 75 °C) to dry, and then roasted at 178 °F (80 °C). Dortmund and Munich malts are first kilned at low temperatures before the malt has dried, then the temperature is slowly raised to 195-205 °F (90-95 °C) for Dortmunder malt, and 210 to 244 °F (100-120 °C)for Munich malt. This process creates flavor and body-building melanoidins from amino acids and malt sugars. Amber malt is well-modified, and then dried and rapidly heated to 200 °F (95 °C). The temperature is then raised to 280-300 °F (140-150 °C) and held there until the desired color is reached.
Crystal and caramel malts are fully modified, then kilned at 50% moisture content. The temperature is raised to 150-170 °F (65-75 °C) and held for 1 1/2 to 2 hours. This essentially mashes the starches into sugars inside the grain husk. The malt is then heated to the final roasting temperature, with the time and temperature determining the Lovibond color index.
Chocolate and Black Patent malts are undermodified (less than 1/2), dried to 5% moisture, then roasted at 420-450 °F (215-230 °C) for up to two hours, depending on the degree of roastiness desired. The high heat helps degrade the starches, so no protein rest is require for these malts even though they are not fully modified. Malts kilned over smoky beechwood fires, as in Bamberg, pick up a rich, heavy smokiness (which is imparted to the beer) from the phenols in the smoke. Whiskey malt is made in a similar manner by smoking over peat fires.
Kilning at the maximum temperature is generally done only until the grains are evenly roasted. They are then cooled to below 100 °F (40 °C) and the rootlets removed. Malts should be allowed to rest for a month or so before being mashed.
Other Malted Grains
The most widely used malted grain besides barley is wheat, which is a key ingredient in German and American wheat beers and used in small quantities in others to improve head retention. It has sufficient diastatic power to breakdown its own proteins and starches, but since it does not have a husk, it is usually mashed with barley malt in order for an adequate filter bed to be formed during the lautering stage. The protein and b-glucan content of wheat is high compared to barley, so a more extensive mash schedule with an extended protein rest may be needed when large quantities are used. Other malted grains used in brewing include rye, oats and sorghum, but these are more commonly used in their raw forms.
The barley corn contains sugars, starches, enzymes, proteins, tannins, cellulose, and nitrogenous compounds for the most part. The starches will be converted into simple and complex sugars by diastatic enzymes during the mash. Proteins in the kernel serve as food for the germ. These are primarily reduced by proteolytic enzymes into polypeptides, peptides and amino acids. Since enzymes are proteins, the protein content of the malt is an indication of its enzymatic strength. Peptides of the B-complex vitamins are also present and necessary for yeast development. The phosphates in the malt are responsible for the acidification of the mash and are used by the yeast along with other trace elements during the fermentation.
Cellulose, polyphenols and tannins are present in the husk and can lead to harsh flavors in the finished beer if they are leached out by hot or alkaline sparge water. Fatty acids and lipids support respiration of the embryo during malting, but oxidative off flavors and low head retention may result if excessive levels are carried into the wort. Hemicellulose and soluble gums are predominantly polysaccharide in nature and for about 10% of the corn weight. The gums are soluble, but the hemicellulose must be reduced by the appropriate enzymes into fractions that permit good head retention, otherwise they may cause clarity problems in the finished beer.
Unmalted cereal grains have been introduced into brewing because they offer a cheap source of carbohydrates and tend to make a minimal contribution to the wort protein level. They can therefore be used in conjunction with high-protein malts such as American 6-row to give a more fermentable wort and a less filling beer. The starches must be gelatinized before mashing, either by doing a preliminary boil in the double-mash procedure or by flaking them through hot rollers. The most common cereal grains are corn (flaked maize, refined corn grits, corn starch or corn grits), rice grits, sorghum (in Africa), flaked barley, flaked rye and wheat (hard red winter wheat or flaked wheat). The corn and rice adjuncts are used heavily in the American light lager styles, while raw wheat is a key ingredient in Belgian white and lambic beers.
An adjunct is defined as any unmalted source of fermentables in brewing. These include corn and cane sugars, which provide a cheap source of sugar, but are fully fermentable and tend to yield more alcohol and dry out the beer. Honey is a common adjunct in specialty beers, and although it contributes some aromatics, the high sugar content tends to make a beer thinner and more alcoholic than its all-malt counterpart. To achieve a fuller palate, malto-dextrin syrup or powder may be used, but the dextrin content may also be increased by adjusting the malt bill or mashing procedure. Finally, adjuncts that add color, flavor and fermentables include caramel, molasses, maple syrup and licorice.
Beer color is determined by the types of malts used, and is an important characteristic of any style. Two scales are used for color determination – the EBC scale used in Europe, and the SRM scale in the USA. Both scales go from low to high, with low numbers referring to lighter colors. For example, an American light lager would be around 2-3 SRM, a Pilsner between 2-5, an Oktoberfest in the 7-14 range, and a Dunkles Bock in the 14-22 range. Some stouts can be over 60 degrees in color and are essentially opaque. The beer color is primarily determined by the malt, but factors such as the intensity and length of the boil also play a role. For a detailed discussion of beer color, the reader is referred to Ray Daniels’ three-part series on beer color that begins in the July/August 1995 issue of Brewing Techniques.
- Dave Miller, Dave Miller’s Homebrewing Guide, (Garden Way Publishing, Pownal, VT 1996).
- Gregory J. Noonan, New Brewing Lager Beer, (Brewers Publications, Boulder, CO, 1996).
- George Fix, Principles of Brewing Science, pp. 22-47, 87-107 (Brewers Publications, Boulder, CO, 1989).
- George and Laurie Fix, An Analysis of Brewing Techniques, pp. 10-14 (Brewers Publications, Boulder, CO, 1997).