"Porter's praise demands my song, Porter black and Porter strong." -Anon. (c.1800)
The brewing process is a truly fascinating one whereby seemingly magical means a mixture of malted grain, water, and yeast are turned into a delightful frothy beverage that has been enjoyed for centuries. To me it is particularly fascinating that the brewing process has been going on for so long, being done by people who have had no idea of the complexity of the science that they were using.
Evidence indicates that the first beer brewed was by the Egyptians or Mesopotamians about 4,500 years ago(4). In ancient Mediterranean cultures, it had been discovered that wetting barley, allowing it to germinate, and drying it gave the barley a sweeter taste and caused it to last longer in storage. No doubt this was discovered by someone who once left their barley out in the rain and tried to salvage the mess by drying it. The resulting porridges and breads tasted better and everyone was happy. Then one day some poor sap left his porridge in the rain and it ended up sitting there for a few days. When the mess was discovered, it was a bubbling liquid. Some brave soul drank the liquid and discovered that not only did it taste good, but that it provided him with a mild sense of euphoria. However crudely it happened, the first beer had been brewed.
This paper will examine the processes behind brewing to explain how and why they work. In addition, the vocabulary used in brewing will be explained in lay terms as the terms appear for further clarity. There are three main phases in brewing: malting the barley, mashing the grains, and the fermentation process. I will now proceed to explain the first two of these phases in detail.
Malting involves germination of barley grain until its starchy food store, the endosperm, has suffered some amount of degradation by enzymes(3). When malting barley for use in beer, there are two things one must be concerned about: First, how much degradation the endosperm experiences, and second, how great the accumulation of enzymes in the grain is. What the maltster (one who malts) is unconcerned with is the growth of the germ or embryo, which is incidental to malting and leads to the unwanted depletion of the endosperm material through degradation of the embryo.
Not all varieties of barley are well suited for use with brewing, however. The criteria that a barley variety must stand up to are: rapid and synchronous germination of the grains, even degradation of the endosperm by enzymes, an adequate complement of enzymes in the barley even after kilning (which is the next step in malting), and low levels of fibrous material and nitrogen. The maltster wants little nitrogen in his barley because the endosperm not only contains starchy material but also proteins. Although proteins in soluble form are essential to the growth of a young plant, they happen to displace starch. Excessive proteins in the grain prolong the process of malting, making the process more difficult and more expensive. Not only that, but an excessive quantity of proteins in beer reduce both the quality and shelf life of the beer(2). Nitrogen is one of the three atoms in an amino group (the other two are hydrogen atoms) that forms part of all amino acids which in turn are the building blocks of proteins(1). Therefore, a high nitrogen content in a barley variety indicates the presence of large amounts of proteins.
Not all varieties of barley are equally suited for brewing beer. There are two main varieties of barley, two row and six row. In the ear of barley there are three single-flowered spikelets at each node of the rachis (the center axis). These alternate on the rachis so that the triplet of spikelets immediately above or below one triplet is on the opposite side of the rachis. This arrangement give six rows of spikes. In both varieties the median spikelet is fertile and develops a grain. In the so-called six row varieties, all four of the lateral spikelets are fertile and also develop grain, but in the two row varieties the lateral spikelets are sterile, producing no grain(2), as seen in Figure 2. The main difference between the two biochemically is that the two row varieties have a lower enzyme production potential than the six row while maintaining a higher extract yield per kernel(4). We will seen why greater quantities of enzymes are desired when examining the mashing process.
During the earliest stages of this process the action of various enzymes begins dissolving the walls of the cells of the endosperm(2). This liberates the starch molecules by a process called modification. Modification is defined as the degree to which the starchy endosperm is converted to soluble malt starch. Full modification also results in the conversion of long protein chains into usable yeast nutrients in the form of amino acids. Fully modified malt does not need to undergo the protein rest phase of mashing. When the malt is mashed, the diatase that is formed here operates on the starch to bring about its disintegration and solution forming a sweet sugar solution know as wort, from which beer is made(2). After the endosperm has been degraded by enzymes, the maltster terminates the growth of the embryo by drying the grain. Then the maltster usually continues the drying process past the point necessary for arrested growth of the embryo with a process called kilning.
Kilning the malted grains produces a readily milled, stable product that may be stored for long periods, and from which roots may be easily removed. The process of kilning finishes the transition of malt from green malt to finished malt. The so-called 'green-grain' flavor is removed and the characteristic odor, flavor, and color of the malt variety is developed(3), but only to a small extent. In kilning green malt the removal of moisture at low temperatures allows for the maximum preservation of the enzymes in the malt and the least development of odor and color. In some experimental malts, the full complement of diastatic enzymes survives when the green malt is dried at 104 F (40 C) in a rapid-air flow system.
After the malt has been kilned (when the moisture content of the malt is about 5%) it is ready to be cured, a process that finishes the development of the character of the grain's aroma, flavor, and color. The type of malt determines "the duration of the curing, the intensity of the curing, the degree of modification when the green malt is loaded onto the kiln, and the moisture content of the malt at which curing is begun."(3) In general, the more modified the green malt is, the moister it will be at the onset of curing, causing the final color to be darker, the flavor to be richer, and the aroma to be more noticeable. The temperatures used to cure malt are much higher: for pale malts the temperature is usually about 176 F (80 C), and for dark malts the temperatures used are between 203-221 F(95-105 C)(3). After curing, the malt is ready to begin the process of mashing.