Whether you know it or not, chemistry drives every step of the brewing process. It affects every quality of the beer, from it's flavors to it's color, and even alcohol content. This is why, as a home-brewer, it is essential to understand at least some of the basics of brewing chemistry. While the minute details of this process can get very complicated, it is possible for a non-chemist to understand the basics without much difficulty. The following is designed as a basic introduction to the principles of the chemistry behind the brewing process. In some cases, definitions of words are provided at the end of the section. These are designated by a number (#), which appears after the word in question.
Cheers!
Cheers!
You are probably familiar with the four ingredients of beer by now. They are malted barley, hops, yeast, and water. Each of these ingredients serves a specific function in beer making. Malted barley provides the sugar needed to make ethanol, plus amino acids and lipids necessary for healthy yeast growth. Hops adds flavor to balance the sugary taste of the malt, but also provides essential oils which act as a natural preservative. Yeast is a living organism, which converts sugar into ethanol and carbon dioxide. Water should not affect the aroma or flavor of the beer, but the compounds in the water used have an impact on many of the metabolic cycles which occur in the yeast.
|
1. Malting and Kilning
Malting and kilning are the processes by which barley is turned into "malt", which is then used to brew beer. Most home-brewers do not generally undertake this process on their own, and instead buy already prepared malted barley. However, since this process can seriously effect the flavor of your beer, it will be helpful to know a little about what goes on during this process.
Malting and kilning are the processes by which barley is turned into "malt", which is then used to brew beer. Most home-brewers do not generally undertake this process on their own, and instead buy already prepared malted barley. However, since this process can seriously effect the flavor of your beer, it will be helpful to know a little about what goes on during this process.
This is a simplified diagram of a barley seed. As you can see, most of the barley seed is taken up by the starchy endosperm. During malting, the barley is soaked in water until the seed coat, or bran, begins to break down and germination (1) begins. During this brief germination period, various enzymes (2) are released, which are designed to break down the endosperm. In normal germination, the endosperm would be broken down into small pieces which supply the nutrients the seed needs to grow. In the case of brewing beer, this process is stopped after the seed coat breaks down enough for the brewer to access the internal starch. At this point, some of the starch is converted into sugars, but we will discuss that in more detail during the mashing process.
|
Barley undergoes a "kilning" process which includes either toasting or roasting. Just like with any food, as you change the heat profile of it, it changes the quality of the product, such as browning meat. This browning is caused by a chemical reaction known as the "Maillard Reaction". This reaction combines simple sugars and amino acids (both which come from the starchy endosperm) to create a variety of cyclic "flavor molecules". One of these flavors that is created is a polymer (3) called melanoidin, which is brown in color and produces the characteristic browning effect
we see in meat and bread. This browning of the barley helps to produce the complex colors and flavors beer is known for. |
2. Mashing
Mashing is a brewers term for steeping the malt in warm water in order to allow the enzymes to break starch down into ferment-able sugars. There are multiple methods of doing this, but the end result is the same. The barley and water mixture (mash) is heated without boiling to the ideal active temperature of the enzymes which then process starch into sugar. If the mash is boiled right away, we will denature (4) the enzymes and not allow them enough time to react with the starches.
Mashing is a brewers term for steeping the malt in warm water in order to allow the enzymes to break starch down into ferment-able sugars. There are multiple methods of doing this, but the end result is the same. The barley and water mixture (mash) is heated without boiling to the ideal active temperature of the enzymes which then process starch into sugar. If the mash is boiled right away, we will denature (4) the enzymes and not allow them enough time to react with the starches.
Starch is composed of carbohydrate building blocks called glucose. Glucose exists in two different forms, a linear form and two separate cyclic forms. These two cyclic forms are called the alpha and beta forms. As you can see from the diagram, the linear form of glucose becomes the cyclic form when the second-to-the-bottom oxygen atom attacks the number 1 carbon near the top. (This is called the anomeric carbon.) The oxygen atom can attack from either side of the anomeric carbon, creating the two separate forms of cyclic glucose. Notice that the only difference between these two forms is the position of the highlighted OH group. There are typically more alpha than beta glucose molecules in a solution.
|
There are two important starches that are found within a barley seed, amylose and amylopectin. Amylose is a linear polymer of glucose with alpha linkages which connect carbons number 1 and 4. Anylopectin is a branched polymer of glucose which is connected by alpha linkages between carbons 1 and 4 as well as alpha linkages between carbons 1 and 6. Two enzymes, alpha and beta amylase, catalyze the hydrolysis (5) of alpha linkages, and break the long-chain starches up into much smaller sugars, such as maltose, glucose, and sucrose. Each of these enzymes has their own ideal working temperature, and the temperature that the mashing is performed at affects which enzyme is dominant in this process. Alpha-amylase leaves smaller molecules behind, and gives a more malty, full-bodied beer. Beta-amylase leaves larger sugars behind, and gives a crisper, less malty beer.
|
3. Boiling and Hopping
Before the boiling and hopping process occurs, the starch from malt has been converted into the sugar needed for the yeast. Boiling is done at this point to decrease the pH level and make the wort (6) ready for hopping. Boiling the wort also sterilizes it, killing bacteria and any active wild yeast. Raising the temperature will also stop all enzymatic activity by denaturing the proteins. Finally, boiling at this point in the process helps to coagulate (7) the proteins so that they fall out of solution and the beer will not be left cloudy.
Before the boiling and hopping process occurs, the starch from malt has been converted into the sugar needed for the yeast. Boiling is done at this point to decrease the pH level and make the wort (6) ready for hopping. Boiling the wort also sterilizes it, killing bacteria and any active wild yeast. Raising the temperature will also stop all enzymatic activity by denaturing the proteins. Finally, boiling at this point in the process helps to coagulate (7) the proteins so that they fall out of solution and the beer will not be left cloudy.
Near the end of the boil, hops are added. Hops add bitter resins to help counteract the sweet malt flavor. The bitter flavors come from alpha and beta acids. Alpha-acids are virtually insoluble in water, however, while the hops are boiled, the alpha-acids are converted to iso-alpha-acids which are much more soluble. Often, hops are selected to have more alpha-acids than beta acids, though beta-acids contribute to the bitter flavor as well. Another extremely important function of hops is that they carry essential oils. Essential oils are so volatile (8) that they carry very strong aromas. There can be up to 250 different essential oil components in hops, giving beer it's strong, floral aroma. The most prominent essential oil in hops is humulene.
|
4. Fermentation
The processes of yeast, like most biological processes, are very chemically complex. However, the function of yeast can be summed up quite easily by saying that yeast intakes glucose, and excretes ethanol and carbon dioxide. The yeast uses this process to create energy. Ethanol is a waste product because the organism can not acquire any more energy from this molecule. This process is considered an "anaerobic" process because it occurs without the presence of oxygen.
The processes of yeast, like most biological processes, are very chemically complex. However, the function of yeast can be summed up quite easily by saying that yeast intakes glucose, and excretes ethanol and carbon dioxide. The yeast uses this process to create energy. Ethanol is a waste product because the organism can not acquire any more energy from this molecule. This process is considered an "anaerobic" process because it occurs without the presence of oxygen.
The many byproducts of yeast greatly impact the flavor and aroma of beer for better or worse. Two common compounds that are released by yeast are acetaldehyde, which gives off a green apple type aroma, and sulfur, which can be reminiscent of rotten eggs. Choosing an appropriate yeast for the beer you're brewing is a critical step in the brewing process, because different strains of yeast leave behind different types and amounts of chemical byproducts which can greatly effect the overall flavor of the beer.
|
All of the in-depth chemical processes that occur while brewing are far too technical for the average reader. However, we hope you can see how a basic knowledge of the chemistry of beer can aid you in developing the best brew possible. Please feel free to ask for more in-depth
information by emailing the stlbrews crew.
information by emailing the stlbrews crew.
Definitions:
all definitions adapted from Merriam-Webster Online English Dictionary (www.merriam-webster.com)
1. germination- the process by which a plant grows from a seed
2. enzymes- any substance produced by a biological organism which acts as a catalyst in a specific biological reaction
3. polymer- a large molecule which is composed of many repeating subunits
4. denature - destroy the characteristics of a protein by disrupting its molecular configuration
5. hydrolysis -the chemical breakdown of a larger compound into smaller subunits due to reaction with water
6. wort - the liquid drained off the mash that will be used to ferment and make beer
7. coagulate - change to a solid or semisolid state
8. volatile - easily evaporated at normal temperatures
all definitions adapted from Merriam-Webster Online English Dictionary (www.merriam-webster.com)
1. germination- the process by which a plant grows from a seed
2. enzymes- any substance produced by a biological organism which acts as a catalyst in a specific biological reaction
3. polymer- a large molecule which is composed of many repeating subunits
4. denature - destroy the characteristics of a protein by disrupting its molecular configuration
5. hydrolysis -the chemical breakdown of a larger compound into smaller subunits due to reaction with water
6. wort - the liquid drained off the mash that will be used to ferment and make beer
7. coagulate - change to a solid or semisolid state
8. volatile - easily evaporated at normal temperatures