In the past, I’ve written about the flavor and scent of beer: what the bitter principles are, what off flavors are, or even what will make your beer smell bad. Something that hasn’t yet come up is the color. Most beers are some shade of yellow/brown, with tints of other colors occasionally coming in – some reds, oranges, etc.
Where does it all come from? As you know, the fermentable sugars in beer are extracted from malted barley. The malting process involves soaking barley in water to allow it to germinate and produce enzymes (these enzymes are later used in the brewing process to break down starches into more simple sugars). Before the barley sprouts, the water is removed and the barley is roasted in an oven (or dried by hot air). The length and temperature of the roasting “toasts” the grain, and the degree to which you toast your barley contributes to the darkness of your beer. The scale used to typically rank beer colors is shown the picture.
So what’s going on when you roast barley? It turns out that the process of roasting barley is governed by a series of reactions referred to collectively as a Maillard reaction. The Maillard reaction (named after Louis-Camille Maillard, a French Chemist) is a process of non-enzymatic browning that gives rise to a variety of flavors in food. The same process that makes your beer brown and gives it that roasted/malty flavor governs the flavors and color in the browning of a steak, coffee, maple syrup, fried onions, and a whole bunch of other cooked foods. The Maillard reaction stands in contrast to other reactions in brewing such as the breakwdown of sugars by beta-amylase or fermentation — both of which are controlled by various enzyme catalysts. The Maillard reaction, on the other hand, occurs in the presence of heat and nothing else.
When you heat up germinated barley (or bread, or a steak) sugars can react with amino acids in proteins present in the grain/meat. It is this non-enzymatic (heat induced) condensation between the sugars and those amino acids that is a Maillard reaction. [As an aside, a “condensation” reaction is when two larger molecules come together and expel a smaller molecule, often water. This type of reaction is so named because early chemists noticed water condensing on the sides of their flasks during the reaction process.] Carmelization, a related process, refers to the non-enzymatic heat induced browning reaction of a sugar alone (The heating of a compound in the absence of other components is also referred to as pyrolysis). In contrast to enzymatic reactions, which often produce a single product with very high selectivity, Maillard reactions produce hundreds of products from relatively simple starting materials. Exactly which products are present he mixture can be influenced by a number of factors, including temperature, water pH, mash/steep time, kettle boil time, hops, fermentation, filtration (or lack thereof), and oxidation.
In any case, some of the products of the Maillard reaction, like many organic compounds, are somewhat brown in color. Surprisingly, the exact components of this mixture are relatively poorly characterized — this is likely a consequence of the fact that the products themselves are difficult to generate in a selective way to study.* Some Maillard products have been characterized, however. Some components of the Maillard mixture are nitrogen containing molecules that are responsible for some of the “baked bread” smell you might find in your malted barley (and, uh… in roasted bread). Some other structures that have been isolated are more “sugar-like” but with nitrogen substitutions, and others are heterocyclic, meaning that they contain rings with atoms other than carbon. In any case, a huge number of changes can happen to sugars during the Maillard process.
Beer color is rated on a scale of degrees Lovibond (named after Joseph Williams Lovibond, a British brewer from the 1800’s and early 1900’s who was among the first to try to quantitatively measure beer color). Although you can sometimes measure color spectrophotometrically with a scientific instrument, most often beer color is recorded as compared to international standards, as the truly dark beers are opaque and not really measurable. Changing the type of malted barley, the way you malt the barley, or even the time you steep your grains all have an influence on the color of your beer. Also, it turns out that when you do a google image search for Lovibond, a cute chick turns up. She probably does something unrelated to beer, but we’d probably need more research to figure that out, and I’m no stalker.
The more you know.
* Interestingly, when a Maillard reaction occurs on proteins in your body, (i.e. when sugars condense on proteins in your organs) molecules called advanced glycation endproducts (AGEs) are formed. AGEs have been associated with diabetes and other physiological changes in humans such as changes in metabolism. This is a hotly contested area of research right now. AGEs typically form when you have too much sugar in your diet over long periods of time.