Before the widespread use of hops, herbs were used to stabilize beer, to retard spoilage, to increase palatability and cover brewing failures, to imbue the beer with medicinal qualities, and finally to make beer “stronger” or even hallucinogenic. In Europe herbs had previously been collected, dried, ground, and often blended and traded as a mixture called gruit, (Gruit is the low-German word for herbs)  which was usually added to the kettle during wort boiling. Today, more and more craft brewers are returning to using herbs in order to develop unique flavor profiles.


Antioxidants are naturally found in beer and may have a positive effect on health. An antioxidant is a substance that protects against the oxidation of other molecules. Oxidation is defined as the loss of electrons. Antioxidants function by interfering with the siphoning of electrons from molecules. They may do this by themselves being preferentially oxidized, thereby preventing other materials being oxidized; by blocking the action of oxidizing systems; or by donating electrons.

Antioxidants may be endogenous (i.e., native to the raw materials of brewing), exogenous (i.e., added), or both.Examples of endogenous antioxidants are polyphenols (such as catechin), phenolic acids (e.g., ferulic acid), and Maillard reaction products and enzymes (notably superoxide dismutase, catalase, and peroxidases). Exogenous antioxidants would include ascorbic acid, which, although present (as vitamin C) in many living systems, is not substantially present in those organisms significant in brewing. Sulfur dioxide (metabisulfite) is both endogenous (it is a product of yeast metabolism) and exogenous.

Antioxidants in a brewing context have two significant roles. First, they protect against the oxidation of wort, yeast, and beer, thereby extending beer shelf life and yeast viability. Second, their presence in beer is relevant to the impact of beer on the health of the drinker. The antioxidants in beer are derived from both the malt and the hops, but the levels found will depend on the style of beer and the raw materials and brewing processes used.

Beer contains more than twice as many antioxidants as white wine (of equivalent alcohol content) but only half the amount in red wine, although the antioxidants in beer tend to be smaller molecules than in wine and may be more readily absorbed by the body. Researchers working on animals have suggested a direct effect of antioxidants in beer to reduce the risk of cardiovascular disease.

Halliwell, B., and J. M. C. Gutteridge. Free radicals in biology and medicine. New York: Oxford University Press, 2007. Charles W. Bamforth


Enzymes are proteins possessing catalytic capability, i. e., the ability to accelerate chemical reactions without being changed themselves at the end of the reaction.

The production of beer is critically dependent upon enzymes, whether endogenousenzymes native to raw materials, such as malted barley and yeast, or exogenous (added) enzymes of commercial origin. There is a great diversity of enzymes, including amylases that break down starch, β-glucanases that hydrolyze β-glucans, pentosanases that degrade pentosans, and proteinases that catalyze the degradation of proteins. The molecules acted upon by the enzymes are called “substrates;” the materials produced are “products.” Traditionally, it is the enzymes naturally present in malted barley that will break down grain starches into sugars during the mashing process, and it is those sugars that will ferment into beer.

Optimizing enzyme activity is crucial to the brewing process and dependent on the style of beer brewed and the materials available. The brewer will carefully manipulate the temperature, time, ionic composition, and material concentrations in wort to ensure that the enzymes work in concert to create the perfect beer.

The more enzyme available, the faster the reaction. The relationship between the rate of an enzyme-catalyzed reaction and substrate concentration is not so simple. At a certain substrate concentration the system becomes “saturated,” such that elevating the substrate concentration beyond this point does not lead to the reaction proceeding any faster. This is referred to as “saturation” and occurs because the enzyme binds to the substrate molecule to form an “enzyme-substrate complex” which then breaks down to re-form the enzyme and release the product(s).

The location where the substrate binds to the enzyme and where the reaction occurs is called the “active site.” The shape of the protein molecules determines this and the active site might comprise amino acids from quite distinct parts of the enzyme molecule. Stresses such as heat or changes of pH that will tend to change the interactions in the enzyme molecule will disrupt the active site, prevent substrate binding, and destroy enzyme activity. Enzymes differ in their tolerance of heat and pH.

Temperature and pH also impact directly on the rate of the reaction that the enzyme catalyses. All chemical reactions, including those catalyzed by enzymes, are accelerated by heat according to Arrhenius’ Law. However, heat also disrupts proteins’ three-dimensional organization, thereby deforming the active site. Thus the net rate of reaction observed is a balance dependent on how resistant the enzyme is to heat. Enzymes in mashes such as α-amylase and peroxidases are very resistant to heat, whereas others like β-glucanase, β-amylase, and lipoxygenase are much more heat sensitive. The enzyme α-amylase, essential in starch breakdown during mashing, is also stabilized by the presence of calcium ions.

pH also impacts the catalytic process as well as the stability of the enzyme. It is likely that the amino acids functioning within the active site will only do so under certain charge conditions and this will be directly determined by the local pH. Most enzymes of relevance in mashing tend to function optimally in the pH range of mashes (between five and six). Enzymes are susceptible to inactivation by other agents (“inactivators”). One such substance is the copper ion that binds thiol groups. Other molecules (“inhibitors”) can block enzyme activity reversibly: i.e., if they are removed then enzyme activity is restored.

Bamforth, C.W. Current perspectives on the role of enzymes in brewing. Journal of Cereal Science, 50 (2009): 353–57.
Lewis, M. J., and Bamforth, C.W. Essays in brewing science. New York: Springer, 2006


Finings are processing aids added to unfiltered beer to remove yeast and protein haze. During fermentation yeast cells and beer proteins largely derived from the malt form a colloidal suspension that appears as a haze. A colloidal suspension forms when very small, charged particles are suspended in a liquid. An electrostatic charge, known as a zeta potential, repels one particle from the next and serves to impede the settlement of the solid particles from the liquid phase.

In beer styles originating in the British Isles this turbidity was traditionally removed by the addition of a solution of a charged polymer solution. Examples include isinglass, gelatin, and gum arabic solutions. In unclarified beer, yeast cell walls carry a negative charge. Isinglass and gelatin solutions are proteins that carry a positive charge. When added to newly fermented beer, the charged finings interact with the yeast and neutralize the zeta potential present on the cell wall. This eliminates the repulsive forces and sticks the yeast cells together to form a larger particle called a floc. These larger particles settle considerably faster than they would otherwise, as dictated by Stokes’ law.

The neutralization happens quickly and the use of finings can be remarkably efficient, so much so that it enabled British brewers to present fresh, unfiltered, cask-conditioned beer with a pleasing clarity without the need for filtration or extensive settling time. Some brewers will use finings to reduce the yeast suspended in beer before preparing a beer for filtration.

Preparations intended to precipitate proteins rather than yeast are referred to as auxiliary finings. Often derived from carrageenans or alginates, these preparations carry strong negative charges that attract and form flocs with positively charged proteins. Although yeast finings such as isinglass can be used in conjunction with auxiliary finings, they cannot be added at the same time because each would neutralize the other, rendering both fining agents ineffective.

According to the Oxford Companion to Beer
Ian L. Ward

Foam Controls

Foam, or head, atop a glass of beer is widely considered to be among its most alluring physical traits. It is the main attribute that visually separates beer from other sparkling drinks, and it is also quite important for the mouthfeel of many beers. As one drinks a beer, some of the foam is also consumed, giving the beer a thicker, smoother texture. Brewers, of course, know this, and therefore foam formation and stability are an essential part of overall beer quality. Beer foam has been studied extensively and brewers work hard to make sure their beer has good “head retention.”

Beer is, among other things, a supersaturated solution of carbon dioxide (CO2) and will not foam unless encouraged by agitation or by the presence of nucleation sites such as particles in beer or scratches on glasses. The more CO2, the more foam will be produced.

Foam is an inherently unstable phenomenon because of the huge increase in surface area within an aqueous system that is counter to the force of surface tension. That beer foam is stable, unlike that in richly carbonated beverages such as champagne and sodas, is due to the presence of surface-active agents in the beer.

The key physical process leading to the collapse of beer foam is disproportionation. In this phenomenon, gas passes from small bubbles to adjacent larger bubbles, leading to a drastic reduction in the number of bubbles and an increase in the size of remaining bubbles such that they become unattractive. The lower the temperature, the more stable is the foam. More important, it is advantageous to have a uniform distribution of bubble sizes, preferably small bubbles because then liquid beer drains more slowly from the foam, which helps stabilize the head. This focuses attention onto the sites and mechanism of foam formation; devices in dispense taps and deliberate scratching of the bottom of drinking glasses should be such as to enable the production of uniformly small bubbles.

The main foam-stabilizing agents in beer are hydrophobic polypeptides derived from grain. These molecules cross-link with the bitter iso- α-acids derived from hops to render the foam more rigid and not only more stable but also able to adhere to the sides of the glass as the beer is consumed (cling or lacing). The reduced hop preparations used to afford light protection to beer are especially good foam stabilizers; however, the foams may appear coarse, lumpy, and less appealing.

Other materials that can support foaming include metals. Zinc is especially efficacious and has an advantage over metals such as iron that were once used in that it does not promote oxidation. Melanoidins have some foam-stabilizing capability, meaning that darker beers frequently have superior foaming properties. Some brewers add foam-stabilizers such as propylene glycol alginate to the beer, and some brewers introduce nitrogen gas into the beer, which gives much more stable foams (though at risk to the aroma of those beers expected to have hoppy notes). This is the reason for the creaminess and retention of the heads on most draft Irish stouts such as Guinness.

The most frequent cause of poor foaming of beer is the presence of foam-negative materials, most notably lipids introduced in the process or as part of food consumed alongside the beer, and detergents that have not been properly washed from the glass or dispense lines. Alcohol is also foam-negative, so stronger beers tend to have less foam stability pro rata. Also damaging to foam are proteolytic enzymes, either those such as papain added as haze-preventatives, or those secreted from stressed and old yeast. Foam is more durable in pasteurized beer because the heat treatment destroys such proteinases.

Though most consumers want and expect to see at least a few centimeters of foam on top of a beer, there are wide cultural differences. In Britain, for example, consumers in the south, when served cask-conditioned ales, widely prefer the liquid level of a pint to nearly reach the rim of the glass. A cap of foam should float above, but no more than that. In northern England, however, the consumer expects a frothier foam, which is often achieved by a device called a “sparkler,” attached to the spout of hand-pump assembly. The sparkler causes the beer to spray violently into the glass, which foams the beer even though cask-conditioned beers contain only light carbonation. It is customary to use over-sized glasses, in which the pint measure is marked by a line near the top of the glass, but which leave plenty of room for the foam to feature. The quality of beer foam remains a topic of debate among beer drinkers, though hopefully over pints.

Bamforth, C.W The relative significance of physics and chemistry for beer foam excellence: Theory and practice. Journal of the Institute of Brewing, 110 (2004): 259–266.
Evans, D. E., Bamforth, C.W. “Beer foam: Achieving a suitable head.” In Beer: A quality perspective, ed. C.W. Bamforth, 1–60. Burlington, MA: Academic Press, 2009.

Water Agents

Beer is mostly water, so it stands to reason that the water used to brew that beer should be of good quality. In this course, we make an arbitrary distinction between quality and composition. Good quality water is free from contaminants and sediment, has a flavor that’s pleasant enough to drink on its own, and is not heavily chlorinated. Most municipal tap water is of good quality. Water composition, on the other hand, refers to the relative quantities of dissolved minerals, ions, and salts.

All good beer requires good quality water: This is a necessary but insufficient prerequisite. To brew the best beer possible, you need to consider water composition and check that it is suitable for brewing in general, as well as for the style you wish to brew. Virtually no knowledge of water is needed to brew from extract, apart from understanding that bad-tasting tap water does not make good beer. Once you start mashing grain, though, water composition plays a greater role. Dissolved compounds in the mash water interact with compounds in the grain in different ways and change conversion and flavor extraction.

There’s a reason that Burton-upon-Trent is so intimately associated with India Pale Ale and that Pilsner developed in Plzeň (Pilsen). These two cities have vastly different water compositions, and the beer styles they nurtured owe as much to the local water as they do to the selection of malts, hops, and yeast.

Water, or the formula H₂O tells us that a water molecule is comprised of two hydrogen atoms (H + H = H₂) that are chemically bonded to one oxygen atom (O). H + H + O = H₂O. But 100 percent pure H₂O doesn’t really exist except in theory. In reality, all water contains other dissolved substances. Even if you could completely purify water down to just hydrogen and oxygen in a 2:1 ratio, the water molecules themselves would still give and take each others’ hydrogen atoms to a certain degree.  It isn’t all that important to understand the chemistry of the hydroxide and hydronium ions except to understand that these negative and positive ions are free to interact with the positive and negative ions of other dissolved substances.

pH is nothing more than a measure of how acidic a substance is. For completely arbitrary reasons, pH is measured on a scale of 1 to 14 (actually, it’s not 100 percent arbitrary, but knowing the reasons won’t make you a better brewer).

In regular water, the hydronium and hydroxide ions always balance one another, which is why absolutely pure water is neither acidic nor basic. It has a pH of 7 and is neutral. However, as soon as ions from other substances are dissolved in that water, they throw off the balance, and the pH goes in one direction or the other, depending on the blend of those dissolved substances. So, given that we want the mash pH to be in the 5.2 to 5.6 range, which is acidic, and given that dissolved substances can affect that pH, our main goal as brewers is to ensure that the blend of dissolved ions and molecules results in a mash pH that’s in our target range.

Bamforth, C.W The relative significance of physics and chemistry for beer foam excellence: Theory and practice. Journal of the Institute of Brewing, 110 (2004): 259–266.
Evans, D. E., Bamforth, C.W. “Beer foam: Achieving a suitable head.” In Beer: A quality perspective, ed. C.W. Bamforth, 1–60. Burlington, MA: Academic Press, 2009.

Yeast Nutrients

Work with yeast (or microbiologists) for any appreciable length of time, and you’re bound to hear about the benefits of yeast nutrient. Added to a starter, nutrient helps promote healthy growth of the colony. Poured into mead, wine, or cider must, supplemental nutrients ensure that our single-celled fungal friends have enough goodies to complete fermentation and reduce that awful, rotten-egg sulfur smell. And a little nutrient goes a long way toward helping big beers reach terminal gravity.

Both Wyeast and White Labs make Nutrients (Wyeast Nutrient Blend and Servomyces, respectively). Every product is different, but some of the most common constituents of a good nutrient blend include:

Diammonium phosphate (DAP) is a water-soluble salt that is often included in plant fertilizer to increase the pH of soil. It also delivers valuable nitrogen and phosphate to yeast cells. Wort is generally rich in nitrogen, but a little supplementation can help high-gravity beers complete fermentation. Phosphates also help ensure smooth fermentation of worts that contain large portions of non-malt adjuncts.

Amino acids are necessary for creating proteins and for reproduction. Yeasts can actually make most of their own amino acids, but there are a handful, termed essential amino acids, that cells must pull in from the wort they’re in. If wort happens not to have enough for one reason or another, a little boost of yeast nutrient can help keep your yeast cells happy.

Vitamins and minerals of all kinds—biotin, pantothenic acid, calcium, magnesium, potassium, and many others—are necessary for the reactions that create the compounds yeasts need to do their job. They also serve as catalysts in many of the reactions that take place during fermentation, and some even aid in flocculation and cell wall preservation.

Zinc, which falls under the mineral umbrella is one of the less common essential minerals found naturally in all-malt wort. Zinc plays a vital role in the production of ethanol, which we can all agree is pretty key to the whole beer thing.

Yeast ghosts, or yeast hulls, are basically the water-insoluble skeletons of dead yeast cells, and they’re included in many nutrient formulations, as well as available on their own. Live yeast cells cannibalize these dead cells and feed off the nutrients they contain.

In most standard gravity all-malt worts, you need not worry about yeast nutrient (except perhaps zinc), but it can’t hurt to throw in a pinch or two for good measure. We usually don’t bother with nutrient in the main wort unless we’re brewing high-gravity or high-adjunct beer, but we always add a little to our yeast starters.

Stan Hieronymous