Chapter 12 - What is Malted Grain?
Barley Malt Defined
Figure 69: A simplified diagram of a barley kernel during malting, showing a progressive picture of how the acrospire (the plant shoot) grows along one side of the kernel. As it grows, pre-existing enzymes are released and new enzymes are created in the aleurone layer which "modify" the endosperm (the protein/carbohydrate matrix starch reserve) for the acrospire's use.
Malted barley is the source of the sugars (principally maltose) which are fermented into beer. The malting process allows the grain to partially germinate, making the seed's resources available to the brewer. During germination enzymes in the aleurone layer (Figure 69) are released, and new enzymes are created, that break down the endosperm's protein/carbohydrate matrix into smaller carbohydrates, amino acids and lipids, and open up the seed's starch reserves. The endosperm is composed of large and small starch granules that are packed like bags of jellybeans in a box. The cell walls (bags) within the matrix holding the starch granules (jellybeans) are primarily composed of beta-glucans (a type of cellulose), some pentosans (gummy polysaccharide) and some protein. The box in this metaphor is the outer husk. The degree to which the enzymes tear open the bags and start unpacking the starch granules (i.e. breakdown the endosperm) for use by the growing plant (or brewers in our case) is referred to as the "modification." One visual indicator that a maltster uses to judge the degree of modification is the length of the acrospire which grows underneath the husk. The length of the acrospire in a fully modified malt will typically be 75-100% of the seed length.
If germination continued, a plant would grow, and all of the starches that the brewer hoped to use would be used by the plant. So, the maltster gauges the germination carefully and stops the process by drying when he judges he has the proper balance between resources converted by the acrospire and resources consumed by the acrospire.
The purpose of malting is to create these enzymes, break down the matrix surrounding the starch granules, prepare the starches for conversion, and then stop this action until the brewer is ready to utilize the grain. After modification, the grain is dried and the acrospire and rootlets are knocked off by tumbling. The kiln drying of the new malt denatures (destroys) a lot of the different enzymes, but several types remain, including the ones necessary for starch conversion. The amount of enzymatic starch conversion potential that a malt has is referred to as its "diastatic power".
From a brewer's point of view, there are basically two kinds of malted grain, those that need to be mashed and those that don't. Mashing is the hot water soaking process that provides the right conditions for the enzymes to convert the grain starches into fermentable sugars. The basic light colored malts such as pale ale malt, pilsener malt and malted wheat need to be mashed to convert the starches into fermentable sugars. These malts make up the bulk of the wort's fermentable sugars. Some of these light malts are kilned or roasted at higher temperatures to lend different tastes e.g. Biscuit, Vienna, Munich, Brown. The roasting destroys some of their diastatic power.
The diastatic power of a particular malt will vary with the type of barley it is made from. There are two basic varieties of barley, two row and six row - referring to the arrangement of the kernels around the shaft. Two row barley is the generally preferred variety, having a bit higher yield per pound, lower protein levels, and claiming a more refined flavor than six row. However, six row has a little higher diastatic power than two row. Historically, the higher protein level of six row barley (which can produce a very heavy bodied beer) drove brewers to thin the wort with unmalted grains like corn and rice. Brewers were able to take advantage of six row barley's higher diastatic power to achieve full conversion of the mash in spite of the non-enzymatic starch sources (adjuncts).
Besides the lighter-colored base and toasted malts, there is another group of malts that don't need to be mashed and these are often referred to as "specialty malts". They are used for flavoring and have no diastatic power whatsoever. Some of these malts have undergone special heating processes in which the starches are converted to sugars by heat and moisture right inside the hull. As a result, these malts contain more complex sugars, some of which do not ferment, leaving a pleasant caramel-like sweetness. These pre-converted malts (called caramel or crystal malts) are available in different roasts or colors (denoted by the color unit Lovibond), each having a different degree of fermentability and characteristic sweetness (e.g. Crystal 40, Crystal 60). Also within the specialty malt group are the roasted malts. These malts have had their sugars charred by roasting at high temperatures, giving them a deep red/brown or black color (e.g. Black Patent malt). The Lovibond color scale ranges from 1 to 600. See Figure 70. To put this in perspective, most American mega-brewed light lager beers are less than 5 Lovibond. Guinness Extra Stout on the other hand, is comfortably in the 100s. Specialty malts do not need to be mashed, and can simply be steeped in hot water to release their character. These grains are very useful to the extract brewer, making it easy to increase the complexity of the wort without much effort.
Figure 70: Notice the difference in color between the base malt 2L (top), Crystal 60L Malt (below right), and Roasted Unmalted Barley 550L.
Lastly, there are fermentables not derived from malted barley which are called "adjuncts". Adjuncts include refined sugars, corn, rice, un-malted rye and wheat, and unmalted barley. These are not to be scorned, some adjuncts like wheat and unmalted roasted barley are essential to certain beer styles. Whole brewing traditions like Belgian Lambic, German Weizen, and Irish Stout depend on the use of adjuncts.