This Web page assumes that the reader possesses knowledge of basic brewing principles including: mashing, lautering, sparging, sanitation, yeast starters, chilling, aeration, priming, bottling, and oxidation. It also assumes that the reader knows how to use basic equipment including: grain mills, mash/lauter tuns, boil kettles, wort chillers, siphon hoses, and sanitation chemicals.

Most of the concepts described herein are somewhat advanced; hence this work is not intended as a beginner's manual. Its purpose is to expand on basic concepts, give finer points and explain a few chemical reactions, thereby helping brewers improve their understanding, processes and products.

During malting, raw barley or wheat is soaked in 57-64º water, which is changed several times in order to remove some of the wild yeasts and bacteria. (Often lactic acid bacteria are added in order to inhibit spoilage organisms, thereby keeping them from hurting mash filterability, malt yield, wort clarity, and beer flavor.) Water enters the micropyle (an opening in the husk where the corn was broken off from the stalk) and wets the embryo (which contains the acrospire) and endosperm (a matrix of about 250,000 cells consisting of starch contained in protein walls). This increases the corn's moisture content from 11-14% to 43-46%. The acrospire, which needs at least 32% moisture in order to germinate, springs to life and produces hormones that journey, via the water medium, to the aleurone, which is a membrane located just beneath the husk.

The hormones prompt the aleurone to produce beta glucanase, which chews up the walls of its own cells and the endosperm cells; proteases, which digest some of the endosperm's protein, thereby exposing the starch; and amylases, which attack the starch. This softens the corn over the course of 4-6 days, during which the temperature rises a little, 5-10% of the endosperm is eaten up, and the grain is turned in order to aerate it because germination requires oxygen. The process is stopped by kilning the malt at 122º or higher (over 400º for black malts) for 24-36 hours until the moisture content drops to 2-4%. (Some Belgian grains are dried a bit less; they contain more than 5% moisture, which gives them a shorter storage life than that of other grains.) Barley metabolism stops once moisture goes below 5%. Kilning starts at the low temperature end, and is increased only when half the moisture is removed. This lessens the heat's killing of enzymes (the drier they are, the less susceptible they are to destruction).

Protease activity is referred to as protein hydrolysis, or proteolysis. Proteins are either water-insoluble hordeins or water-soluble albumins (enzymes are albumins). In proteolysis, hordeins are degraded by proteases, which attack the middle of the molecule, releasing polypeptide chains of amino acids. Then peptidases chop these chains one amino acid at a time.

Ale malts are more modified than lager (pils) malts; that is, the enzymes are allowed to work longer. This gives ale malt greater amounts of sugar and amino acids. Ale malts are also kilned at higher temperatures than are lager malts. The higher heat, combined with more abundant sugar and amino acids, produces more color (from melanoidins) and more complex flavors.

Lager malts have higher diastatic power (lower kilning temperature is easier on the enzymes); lighter color; harder kernels; and more S-methyl-methionine (SMM), the dimethyl sulfide (DMS) precursor. SMM comes from the germinating embryo. Pale malt starts out with more SMM, because the acrospire is allowed to germinate a little more, but the SMM is broken down into DMS during malting, and the DMS is largely driven off with the flue gases. The result is that lager malt, which is kilned at a lower temperature, retains more SMM and DMS than pale malt does. The rest of the SMM is broken down during boiling, with most of the DMS being evaporated off. (SMM is not broken down during mashing because the minimum temperature required is 176º.)

Lager malt is good for beers in which color and malt flavor/aroma are not desired, e.g. pilsners and wheat beers. It is not recommended for single infusion mashes because it is higher in unmodified proteins than ale malt is, and therefore should receive a protein rest. It has more potential to produce hazy beers.

6-row malt has more husk, less starch, and more diastatic power than 2-row malt has. The greater husk material means more tannins, which can add astringency. 6-row malt is higher in free amino nitrogen (FAN); high levels of FAN hinder flocculation and make cloudier beers.

Flaked grains are rolled (flattened) but not malted. A protein rest is recommended since no proteolysis has occurred. High-diastatic base grains are recommended for converting flaked grains (American has more diastatic power than Belgian; pils has more than pale).

Mill the malt to crack, not crush it. The husk pieces should be as large as possible (tiny husk pieces can clog the lauter screen). An adjustable mill should be tested with small amounts of grain before deciding on a setting; the test amounts should be at least a handful at a time, because some of the crush comes from several grains being pressed against one another, while individual corns can fall through intact. If a setting that doesn't pulverize the husks also fails to crack some of the grain, running the grain through a second time might crack the intact corns without making the husk pieces too small.

Cracked grain is more susceptible to dampening, hence spoilage, by humidity, resulting in reduced yield and musty tones in the beer. If grain cannot be stored in a dry environment, crack it as close to brewing day as possible.

All grains, especially base grains, contain lots of bacteria (e.g. Lactobacillus, Pediococcus), which fly into the air in the grain dust produced by milling. Therefore milling is best done away from areas that house cooled wort.

Brewing water should not contain chlorine, as chlorine will combine with wort phenols to produce chlorophenols, which have an unpleasant taste. The water should also be free of iron, lead, nickel and tin.

Use spring or filtered water for mashing and lautering (distilled water doesn't have enough ions).

Malt contains many enzymes. Each has a particular temperature range at which it is active, and tends to be most active toward the high temperature end. The proper mash pH range for most of these enzymes to work is 5.0-5.7. Some work better toward the low end, others toward the high end. A pH of 5.2-5.4 is generally regarded as a good compromise. Mash pH is usually a little higher than this, but it can be lowered in several ways.

Phytase, which is active from about 86º to 126º, acidifies the mash by inverting the insoluble malt phosphate phytin to calcium phosphates, magnesium phosphates, and phytic acid (also called phytate). Phytic acid reacts with calcium (always present in malt) to form calcium phosphate and release pH-lowering hydrogen ions. Since phytase is active at protein rest temperature, acidification and protein breakdown can be accomplished at the same time.

It can take hours for phytase to lower pH into the desirable range, and since the temperature range in which phytase works would enable malt's bacteria to grow and sour the mash, a phytase rest (generally called an acid rest; I use the term phytase rest to distinguish it from a ferulic acid rest) is not cost-effective.

Only lager malt has both phytin and phytase, so a phytase rest is not possible with ale malt.

In lieu of a phytase rest, mash pH can be lowered by adding calcium, which reacts with phytic acid to release hydrogen ions, thereby increasing acidity. The chemical reaction is:

3Ca²⁺ + 2HPO₄^2- --> Ca₃(PO₄)₂ + 2H⁺

Note that this works with both lager and ale malt, whether or not a phytase rest is done, because some phytic acid is produced in both malts during malting.

Dark malts help to acidify the wort, so calcium is generally appropriate only for lighter beers. Furthermore, some calcium is present in both barley malt and wheat malt, so it needs to be added only when the mash water is calcium-deficient.

Calcium can be added in the form of calcium sulfate (gypsum) or calcium chloride. (Calcium carbonate [CaCO₃] raises pH because CO₃ is an alkaline ion.) They have different effects on the final product: gypsum (CaSO₄) accentuates bitterness and dryness, while calcium chloride (CaCl₂) affords body and fullness.

Check the calcium content of the water supply and add only enough calcium to bring it up to the desired level, which is 50-100 ppm for most beers, and up to 150 ppm for pale ales. Excess calcium causes too much phosphate to precipitate, thus robbing yeast of a vital nutrient. In one gallon of liquid, one gram of CaSO₄ adds 62 ppm Ca and 147 ppm sulfate; one gram of CaCl₂ adds 72-96 ppm Ca and 127-168 ppm chloride (different sources state different amounts). Weights are used rather than measures because the weight of a teaspoon of a material can vary, especially since calcium salts are sometimes sold as "puffy" pellets rather than powder; use a gram scale for accurate measurements. Excessive sulfate can make astringent beer; using CaCl₂ instead of CaSO₄ will prevent this.

If the water supply already has an adequate calcium level, the mash should acidify just fine. If the pH is still too high, acidify with phosphoric or sulfuric acid.

An elevated pH can cause: poor saccharification, increased viscosity, reduced protein breakdown, darker color, harsh bitterness, poor head retention, and sluggish fermentation (lager yeasts are more sensitive to high pH than ale yeasts are).

When testing the mash's pH, allow the sample to cool first, or else the reading will be lower than actual.

Wheat beers such as hefeweizens and witbiers get their spicy flavor and aroma from 4-vinyl guaiacol, which the yeast produces from ferulic acid (4-hydroxy-3-methoxy cinnamic acid). The mash's ferulic acid content can be increased with a ferulic acid rest at 111-113º. It should be limited to 30 minutes because of bacterial presence. Wheat malt has more ferulic acid than barley malt, which is one reason that wheat malt is used for these beers. (On a side note, corn has four times as much ferulic acid as wheat!) Wheat has no husk. Grists that contain more than 50% wheat (whether malted or raw) should have rice hulls added.

Barley's cell walls are composed of about 75% beta glucans and 25% pentosans. Beta glucans can be problematic because they make beer more viscous and contribute to haze and bottle sediment. There are also membranous proteins that encase starch and will not release it until they're enzymatically dissolved. At least 8 malt enzymes can break down proteins (proteases break down large, haze-forming proteins; peptidases break down smaller proteins and produce FAN). They work best somewhere in the 104-140º range (each enzyme has its own optimal temperature). A protein rest allows proteases and peptidases to work, thereby raising extract efficiency and producing amino acids that fuel yeast growth. A good schedule is to start at 104º, raise to 122º, hold it there for 20-30 minutes, and raise to saccharification temperature.

A protein rest is recommended only for lager and wheat malts because of their high protein content. Ale malts do not require a protein rest because most of their proteins are broken down during malting. Some sources claim that higher-temperature kilning destroys most of ale malt's proteolytic enzymes, so a protein rest is futile; others say that the enzymes survive but doing a protein rest with ale malt can hurt beer's body, head and flavor.

Unfortunately, the optimal pH for some proteases, including beta glucanase, is below that of the typical mash. As a result, protein gum is little affected by enzyme activity, survives the mashing process largely unconverted, increases the risk of a stuck lauter, and makes the extract prone to haze and oxidation. Decoction can help: boiling dissolves protein gum; when the boiled grains are returned to the main mash during a protein rest, the dissolved protein is exposed to proteolytic enzymes. However, keeping the mash temperature down in protease range while adding boiled grains can be problematic.

Before starch can be saccharified (converted to sugar), it must be gelatinized (solubilized) so that it is available to the enzymes. Barley and wheat starch are gelatinized somewhere in the 140º-154º range (each gelatinization temperature measurement method measures a different aspect of gelatinization, so not all methods give the same results). Rice and corn require higher temperatures: 172º and 165º, respectively. Flaked grains are already gelatinized because rolling ruptures cell walls and produces heat.

Saccharification is accomplished by two enzymes. Alpha amylase attacks starch at random, releasing all sizes of starch fractions: glucose, maltose, maltotriose, and unfermentable dextrins. Common knowledge is that it’s active at 150-158º; however, it is still somewhat active up to 162º (Orval’s saccharification rest is done at 160º). Beta amylase, which is most active at 131-149º, chops off two glucoses at a time (maltose) from the dextrin molecules’ ends. Saccharification rests below 150º therefore yield more highly fermentable worts than those in the 150-158º range, although they take longer because beta amylase needs more time to work than alpha amylase needs. Beta amylase gets denatured somewhere between 154º and 162º (its thermostability differs among barley and wheat species, and increases in thick mashes).

A 154-158º temperature would ensure that all starch granules are gelatinized.

Decoction gelatinizes starch because boiling brings the grains well over gelatinization temperature, so saccharification can be done below 154º without leaving ungelatinized starch.

There are two main forms of malt starch. Amylose, which constitutes 15-30% of the starch, is a straight chain of thousands of glucose units, completely accessible by amylases. Amylopectin, which constitutes 70-85% of the starch, has thousands of glucose units as well but also has branch points that amylases cannot access. These branch points ensure that usually 12-20% of malt sugar remains as unfermentable dextrins, even at saccharification rests below 150º.

Debranching enzymes such as limit dextrinase can access the branch points and thereby convert amylopectin to saccharifiable dextrins. However, very little of these enzymes survive kilning. The vast majority of debranching occurs during malting as a part of the modification process.

Thicker mashes tend to saccharify more quickly than thin mashes do because the greater concentration of reactants decreases the distance between molecules, increasing the reaction rate. Thicker mashes also preserve enzymes better and favor the breakdown of proteins. However, the increased concentration of sugars can inhibit further enzyme activity. Therefore wort fermentability can be increased by starting with a thick mash, and adding some (hot) water halfway through saccharification so the sugar concentration will no longer be high enough to inhibit the enzymes.

The time needed for saccharification is a matter of debate; only an iodine test will definitively indicate that no starch remains. Some sources report that it can be achieved in 20 minutes, but that is only with highly diastatic malt in a thick 158º mash. Furthermore, starch needs time to absorb water before saccharification can begin. Therefore 60 minutes is a general minimum.

Enzymes don't stop working when all the starch has been converted; the dextrins will continue to be broken down into smaller and smaller glucose chains, so that a mash can become more fermentable even at a temperature above the beta amylase range. Thus overnight mashing at 154-158º is a good way to both gelatinize all starches and get ample fermentables.

If not using a RIMS system, it would be a good idea to stir the mash occasionally. This will speed conversion and help to keep an even temperature.

Heating the mash to 168º (mashout) will inactivate alpha amylase, but this is not necessary since having it continue its activity during lautering will have little effect. Its activity would be more efficiently limited by shortening the saccharification rest by the lauter duration. For example, a 90-minute conversion with a mashout followed by a 35-minute lauter can be accomplished via a 55-minute conversion without a mashout followed by a 35-minute lauter. The heat lost during the vorlauf/lauter might drop the mash below 150º, but most of the beta amylase will have been denatured during the alpha rest.

Acidify sparge water to a pH of 5.7 in order to minimize leaching of husk tannins, which can cause astringency, haze, and medicinal flavors in the finished product. Phosphoric acid is best: it contributes phosphate, an important yeast nutrient. Sulfuric acid is okay: it adds sulfate rather than phosphate. Acidify and check pH before heating the water. If acid is not available, adding gypsum or calcium chloride to the sparge water will help somewhat in keeping the pH down.

If the lauter tun is different from the mash vessel, first pour enough sparge water into the lauter tun to cover the straining device; this ensures that there will be enough liquid to keep the grains in suspension instead of allowing them to compact onto and thereby clog the strainer. Then gently scoop the mash into the lauter tun; splashing will cause hot-side aeration. (Most beer oxidation happens during mashing and lautering.)

A vorlauf is recommended before lautering. This involves recirculating some of the runoff back on top of the grains, and should be done until the runoff is mostly clear and free of husks. (Be gentle in order to avoid hot-side aeration.) The vorlauf filters out proteins and other materials that can damage beer.

The wider the mash tun, the shallower the bed. Shallow beds tend to get better extraction and are less prone to sluggish runoffs. A shallow bed is recommended for mashes containing wheat. However, a bed that is too shallow will make the vorlauf less effective. The bed should be at least 6 inches thick.

Sparge water should be 168º or less in order to minimize tannin leaching. It should also be over 160º because the hotter the water, the less viscous the runoff and the less chance there is of a slow or stuck lauter.

Before lautering, put some sparge water into the boil kettle (it's okay to splash - plain water does not oxidize). The runoff tube should be submerged in this water as the wort is transferred to the kettle. This will prevent aeration of the initial runnings. Heat the kettle while it's filling in order to save time and to prevent further enzyme activity. (Do not leave a plastic hose touching the bottom!)

Keep the sparge water level above the grains in order to avoid compaction of the grain bed (which would result in a slow or stuck lauter). If a significant portion of the mash is specialty or non-barley grains, use a hose clamp to moderate the flow; if the wort flows faster than the liquid can filter through the grain bed, this can create a vacuum that will compact the bed.

The lauter rate should be slow at first, in order to avoid compressing the bed. As the wort thins, the bed might or might not expand a bit. If it does, some undesirable material could be released. Increase the flow rate just a bit during the second half of the lauterring process in order to maintain the right amount of suction.

Channelling can be minimized by cutting crisscross cuts in the mash. Do not cut all the way down to the lauter screen.

As the grains get washed, the liquid's pH increases (especially if the sparge water was not acidified) and the sugar concentration decreases. These factors make the husk tannins more susceptible to leaching. Toward the end of lautering, the sparge water temperature should be lowered in order to minimize tannin extraction. This is easily accomplished by leaving the sparge tank uncovered during the lautering process.

Sugar extraction can be measured in points per pound per gallon (PPG), which is the gravity that one pound of grain will give to one gallon of water. PPG is determined by the formula OG × W ÷ GR, where OG = original gravity (the figure to the right of the decimal point, multiplied by 1000; for example, a 1.040 gravity translates to 40), W = gallons of wort, and GR = pounds of grain. For example, if 11 pounds of grain make 5 gallons of wort with an OG of 55, then PPG = 55 × 5 ÷ 11, which equals 25.

The formula for determining how much grain to use is W × OG ÷ PPG. For example, to make 10 gallons with an O.G. of 1.066, if the PPG is 25, then use 10 × 66 ÷ 25, or 26.4 pounds of grain.

Extract efficiency is the amount of sugars extracted relative to how much is available. For example, if the maximum PPG of a grain is determined to be 34, and a brewer gets 25 PPG, then the extract efficiency would be (25 ÷ 34), or 73.5%.

During processing, hops are dried from 75% to 9% moisture at 131-149º.

Hops have hard resins (which are of no concern to us), and soft resins (alpha and beta acids). Alpha acids (humulone, adhumulone and cohumulone) are the primary bittering agents: boiling isomerizes them into iso-alpha acids, which taste bitter. Oxidized hops can’t isomerize so they have reduced bittering power. The most easily extracted alpha acid is cohumulone - it alone is often used for alpha acid rating. Beta acids, also called lupulone, don’t isomerize - they oxidize to compounds that give bitterness, but that are less pleasant than alpha bitterness. Beta acids are insoluble in wort that is at or below 5.5 pH.

Hops should not be boiled for more than 90 minutes. Prolonged hop boils can produce unpleasant flavors.

There are two hop species: Humulus lupulus and Humulus japonicus. The latter has no resins so only the former is used.

The hop flower has more than 250 essential oils, which compose 0.1 to 3% of total hop weight. They're divided into four groups: hydrocarbons, oxygenated essential oils, citrus/piney essential oils, and sulfur-containing essential oils.

Hydrocarbons consist mainly of humulene (not to be confused with humulone) and myrcene. Humulene, which constitutes 18-25% of the oil, undergoes transformation reactions to form epoxides and other oxidation products that contribute to beer aroma. Myrcene (40-70% of the oil) is undesirable (pungent). Both are rapidly oxidized even under good storage conditions. Dry hopping extracts fewer oxygenated products than hot-wort hopping does, leading to increased intensity and stability of humulene aromatics.

Oxygenated hop essential oils are created when oxygen reacts with humulene and myrcene. This can give good or bad flavors. Oxygenation of other hop elements can increase humulene flavor for a few months. Oxygenation usually has a positive effect on myrcene, which is pungent in its unoxygenated form. When oxygenated, myrcene produces the terpenes linalool and geraniol, which impart a floral or herbal character. Mt. Hood is very high in both myrcene and humulene; its oil chromatogram is virtually identical to that of Hallertauer Mittelfrüh [Haunold and Nickerson, "Factors Affecting Hop Production, Hop Quality, and Brewer Preference," Brewing Techniques May/June 1993].

Citrus/piney essential oils give a citrus fruit / pine smell.

Sulfur-containing essential oils can give a skunky aroma (not the same process as is involved in light-struck skunkiness).

Light-struck skunkiness is caused by blue-green light (400-520 nanometer wavelength). When the light strikes an isohumulone molecule, one branch vibrates, eventually breaking off. This broken branch is called an isoprene diene radical. The radical reacts with hydrogen sulfide - which is always found in beer - to produce a mercaptan called 3-methyl-2-butene-1-thiol (MBT), which is exactly the same chemical manufactured by skunks in the glands under their tails. Some people can detect MBT at 0.4 parts per trillion.

The amount of oil obtained in late hop additions is maximized if the hops are added after the heat is turned off and a lid is put on the kettle. This minimizes oil evaporation.

Boiling kills enzymes and bacteria, isomerizes alpha acids, drives off undesirable flavor compounds (e.g. DMS), concentrates wort, and darkens wort via melanoidin reactions. It also causes proteins, which are positively charged, to cross-link with tannins (more specifically, polyphenols; they're called tannins because they're used to tan animal hides), which are negatively charged. They coagulate into chunks called hot break that can be easily separated from wort. Proteins in finished beer can cause haze and excessive sediment (although some proteins are necessary for body and head retention). In addition to coagulating proteins, boiling can also break them into amino acids, which can become part of the hot break or reach the wort to support yeast growth.

As wort starts to boil, proteins form froth on the surface. It can be skimmed off, but this extra work isn't necessary since the proteins will eventually become part of the hot break.

A rolling boil is needed in order to drive off unwanted molecules, bring proteins and tannins together for hot break, and maximize isomerization of alpha acids.

Diacetyl is produced at the beginning of the boil, and is reduced later in the boil.

Boiling de-aerates wort, so the splashing caused by rising bubbles is not a problem.

Larger wort volume increases hop utilization, so if doubling a recipe, multiply the hop bill by somewhat less than 2.

Higher wort gravity lowers hop utilization. Utilization can be increased by doing a separate hop boil in water and adding the "tea" later. However, this separation of hop tannins and malt proteins won't allow optimal hot break formation.

Irish moss (carrageenan), which is made from seaweed, is a polysaccharide (sugar polymer) that sticks to beer solids, making them more sedimentary.

Wort should be whirlpooled at the end of the boil in order to put the hot break in the center of the kettle. Hot-side aeration can be minimized by whirlpooling while the wort is still boiling and then shutting the heat off. Even if whole hops are used, whirlpooling is a good idea because it will make less hot break available to filter through the edge of the hop bed.

Aluminum and stainless steel kettles accumulate beer stone because a thin layer remains between the wort and the kettle, allowing precipitate to bake on. This does not happen to copper because it is "wetted" by hot wort. Copper is needed by yeast at trace levels, but at higher levels can cause oxidation, cell mutation/death, and haze.

The wort should be cooled as rapidly as possible. Slow cooling can raise DMS levels, because DMS is formed in hot wort and will not be driven off if it's not boiling. Fast cooling yields a better cold break and a less hazy finished product.

Gravity can be reduced by adding distilled water (spring or tap water might have bacteria). The lack of ions is okay because the distilled water will be only a fraction of the total volume.

There are three phases of yeast activity:

1. Initial preparation. The yeast takes in nitrogen, sugar and oxygen, and prepares its cell walls. All wort oxygen is used up in 6-24 hours.

2. Aerobic respiration. The yeast grows and multiplies. It produces CO₂ but not ethanol. Each 100g of sugar is converted into about 50g of biomass.
C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6H₂O + 38ATP

3. Anaerobic fermentation. The yeast has used up all of its oxygen. There is still some yeast growth and cell division, but mainly the yeast just eats sugars and produces ethanol, CO₂ and esters. Each 100g of sugar is converted into about 5g of biomass.
C₆H₁₂O₆ --> 2C₂H₅OH + 2CO₂ + 2ATP

100g maltose + 0.5g amino acid --> 5g yeast + 48.8g ethanol + 46.8g CO₂ + 50 Kcal

The first thing yeast does in handling wort sugars is excrete invertase, which breaks the disaccharide sucrose into the monosaccharide isomers glucose and fructose (both C₆H₁₂O₆). Then it eats the glucose, fructose, maltose, and maltotriose, in that order. Once inside the yeast cells, the maltose and maltotriose are broken into glucose units by the enzyme maltase.

Respiration and fermentation start with glycolysis: yeast converts monosaccharides to pyruvate (the ionized form of pyruvic acid). Glycolysis is the initial metabolic pathway of carbohydrate catabolism, and is the only metabolic pathway common to nearly all living organisms. It converts each molecule of glucose or fructose into two molecules of pyruvate. This process happens in the cytoplasm.

In the presence of oxygen, yeast converts pyruvate (CH₃COCOOH) to activated acetic acid (acetyl CoA), which is converted to ATP. Without oxygen, the pyruvate is decarboxylated to acetaldehyde (CH₃CHO) by the enzyme pyruvate decarboxylase. Then the acetaldehyde is converted to ethanol by alcohol dehydrogenase.

Click here to see how the human body metabolizes ethanol.

Aeration is essential to the initial preparation period. In order for yeast to reproduce, its cell membranes must have sterols and fatty acids, which are sparse in wort, but yeast can synthesize them if oxygen is present. In fact, most of the wort oxygen is used up in this process. The wort should not be aerated after the initial preparation period because that can cause high levels of diacetyl to be produced (diacetyl will be discussed shortly). Additionally, ethanol can be reversibly oxidized to acetaldehyde and acetic acid, which can give off-flavors. Wort saturated with air will contain 8 ppm of dissolved oxygen, which is a good level. Wort saturated with pure oxygen may contain up to 40 ppm, which is too high because it can kill every microbe, including yeast.

Underaerated wort produces more esters: yeast will attach fatty acids to the alcohols it produces, making esters. High-gravity worts cannot hold as much oxygen as low-gravity worts can, so they tend to be estery. A high pitching rate can help keep esters down.

The brown layer of scum on top of beer in the initial fermenting stage is full of tannins; hence having a blowoff can improve beer.

Diacetyl (a vicinal diketone more technically called 2,3-butanedione) is produced by yeast during growth. Alpha-acetolactic acid (an intermediate in the pathway leading from pyruvate to the amino acid valine) leaks from yeast, encounters oxygen, and spontaneously oxidatively decarboxylates to diacetyl. The chemical sequence is:

pyruvate --> alpha-acetolactic acid --> diacetyl

Toward the end of fermentation, yeast mops up diacetyl. Yeast should be allowed to stay in the fermenter long enough to do this. Do not chill the wort, or else the yeast could drop out too fast to do its job. If the temperature is raised at the end of fermentation, yeast will settle more slowly and reduce diacetyl more quickly. The reduction reaction is:

diacetyl --> acetoin --> 2,3-butanediol

Acetoin (3-hydroxy-2-butanone) has an unpleasant fruity or musty flavor; 2,3-butanediol has no flavor or smell.

Excess wort oxygen can cause diacetyl production by alternative reaction pathways. Inadequate FAN can hinder diacetyl reduction.

More aerobic respiration means more yeast growth but less flavor. If more esters are desired, use less oxygen or less yeast.

Underpitching can result in sluggish fermentations, excessive sweetness (due to underattenuation), and increased off-flavors.

Overpitching doesn't allow much yeast growth, so fermentation is done mostly with older, weaker cells, resulting in slower fermentation and higher final gravity.

High-gravity worts can undergo the Crabtree effect (also called catabolite repression): the high concentration of sugar causes yeast to go directly into fermentation, even in the presence of oxygen. There is not much increase in cell count, and fermentation is feeble.

Yeast breaks down simple proteins and amino acids, but not long-chain proteins.

Bacteria, most of which are 1-10 micrometers (millionths of a meter) in diameter (cocci are spherical or oval; bacilli are usually rod-shaped, typically under 2 micrometers in width and up to 10 micrometers in length), are prokaryotic cells: all their DNA, protein, carbohydrates, lipids, etc. are contained in a bag of cytoplasm. Yeast, which are roughly 5-10 micrometers in diameter, are eukaryotic: the cytoplasm contains organelles such as mitochondria, nucleus, etc.

Yeast secretes organic acids and digests wort's buffer materials, thereby lowering wort pH to 3.8 - 4.6. This helps inhibit bacterial growth while yeast is unaffected (fungi are more tolerant of acidic conditions than are most bacteria). The low pH is one reason that pathogenic bacteria cannot survive in beer.

Unfortunately the bacteria Lactobacillus and Pediococcus are acid-tolerant. They can also tolerate low oxygen, high alcohol, and hop antiseptics. They produce lactic acid, which sours beer.

Saccharomyces cerevisiae has 16 chromosomes and about 6000 genes. It has about 3 copies of each chromosome, so it is not as prone to mutation as simpler organisms are.

Yeast secretes sulfur-containing molecules such as hydrogen sulfide (H₂S), sulfur dioxide (SO₂) and DMS. H₂S and DMS give off-flavors. SO₂ has positive effects: it binds to stale-tasting carbonyl compounds, producing bisulfite adducts that mask carbonyl off-flavor. Both the bisulfite adducts and the free SO₂ act as free radical traps, thus slowing oxidation. Ample wort FAN helps to limit the production of H₂S (which has a flavor threshold of 10 ppb) and increase SO₂ (25 ppm threshold). Binding to carbonyls usually keeps SO₂ under the sensory threshold.

Yeast produces higher alcohols (fusel oils), which are longer-chain alcohols such as propanol, isoamyl alcohol, butanol and isobutanol. Tyrosol is a phenolic alcohol. Ethyl acetate is ethanol + acetic acid. These can be caused by high fermentation temperature, excessive yeast growth, excessive amino acid levels, excessive ethanol that doesn't allow normal fermentation, excessive trub, and/or oxidation of alcohol into higher alcohol.

Dimethyl sulfoxide (DMSO) is a malting breakdown product of SMM. DMSO can be changed to DMS by yeast, particularly at lager temperatures.

The banana flavor produced by some wheat yeasts comes from isoamyl acetate, and the clove flavor comes from 4-vinyl guaiacol. Adding 120 ppb zinc sulfate to wort can increase yeast's production of isoamyl acetate. The optimal fermentation temperature for producing 4-vinyl guaiacol is 77º.

Lager yeast will ferment raffinose; ale yeast will not. Raffinose is not a significant wort constituent (under 1%).

Rousing yeast removes CO₂ (via the spoon's mechanical action) and puts yeast back in contact with wort to reduce diacetyl.

Cold break is mostly proteins and lipids. It provides nucleation sites for gas release, which keeps yeast in suspension and therefore in contact with wort, and prevents accumulation of excess CO₂ (which would inhibit yeast metabolism). Lipids enable yeast to transport nutrients across their cell walls and cell membranes, and inhibit the formation of some unpleasant esters. However, they’re easily oxidized so they contribute to staling. Lipids are not soluble in water, so they go to the foam and decrease head retention.

If yeast sits too long on the fermenter bottom, it might leak materials that can damage the beer.

Sugars are allowed into yeast cells with the help of permeases. Yeasts can become less attenuative via a mutation where they lose the gene that enables them to synthesize maltotriose permease.

In autolysis, dying cells excrete proteolytic enzymes, breaking down walls of neighboring cells so they can digest their components. Sulfury compounds are released, resulting in a rubbery stench. A warmer medium makes autolysis set in more quickly.

The best way to store yeast is under beer at 33º. This will minimize autolysis.

Wash yeast with a 2.0 to 2.2 pH phosphoric acid solution, at refrigerator temperature, for one hour. The yeast should be pitched immediately after acid washing, otherwise it will deteriorate. Do not attempt to store acid-washed yeast.

Bleach (sodium hypochlorite) is a very cost-effective sanitizer. It yields free chlorine at high pH. Use one ounce per gallon of water, which will give 100-200 ppm of free chlorine. Soak items for at least 10 minutes.

Iodophor is a mixture of iodine, phosphoric acid, and a surfactant. The surfactant makes cell walls permeable so iodine can enter. The iodine combines with cells' tyrosine and thus inhibits microbial protein function. Use enough to give water a light amber color, and soak materials for at least 10 minutes. The solution will lose its killing power within a few hours or days, and mold can then grow on the surfactant. The amber color is a good potency indicator: it fades as potency drops.

Brettanomyces can occasionally survive bleach and iodophor and wake up later in bottles to feed on residual nutrients (I know from experience!). In wood it can metabolize cellobiose (produced by the firing process that cooperages use to toast barrels).

Scrub plastic fermenters with a plastic scrubbie or rough sponge in order to work the bleach or iodophor into the small scratches that house spoilage organisms.

Clean the inside of copper counterflow chillers with products such as Star San or PBW. Boiling-hot white distilled vinegar can also be used. Do not use bleach because it can oxidize and blacken the metal; the oxides can later dissolve into wort, exposing yeast to unhealthy levels of copper during fermentation.

There are 3 ways beers deteriorate: staling, throwing a haze, and infection.

Oxygen stales beer. It can turn ethanol, fatty acids, lipids, proteins and tannins into undesirable products.

A compound oxidizes by giving up electrons. A compound is reduced by accepting electrons. One compound cannot oxidize unless another one is reduced.

Hot-side aeration oxidizes mash and wort components such as melanoidins and phenols. Oxidized constituents can react with alcohol in bottled beer and produce staling aldehydes, even in the absence of headspace oxygen; or give up their oxygen, which will then oxidize other compounds. Reduced constituents can act as flavor protectors: they react with oxygen and thus prevent oxidation of beer components. This delays, but does not indefinitely prevent, the emergence of stale flavors.

The first sign of oxidation is usually loss of hop flavor/aroma.

When bottling, the first unit of wort to enter each bottle gets aerated as it splashes in. Spring-loaded bottle fillers increase the splashing effect. Aeration can be minimized by not using a spring-loaded tip. Wort flow can be stopped/started with a hose clamp or a Phil's Philler.

Headspace is the primary source of oxygen in bottled beer. Filling bottles to the rim decreases oxygen content. Unfortunately, some headspace is necessary for proper carbonation, and lack of headspace can cause bottles to break since there is no cushion for pressure. Therefore a little headspace is a necessary evil.

Haze is caused principally by the cross-linking of certain oxidized polyphenols (tannins) and proteins. Cold storage helps protein-phenol complexes settle. However, store malty beers in a cellar, not a fridge, because long-term refrigeration causes malt flavor particles to drop out.

Isinglass (collagen solution derived from certain species of fish) helps clarify beer because collagen has a positive charge at wort pH, while yeast and other particulates have a negative charge. They form an attracted complex, and the agglomerates sediment readily. Isinglass works best at 50-60º.

Over time, bitterness decreases and sweetness increases. This is one reason that barleywine needs to be quite bitter at the outset.

Serve in a clean class; detergent, cooking fat, lipstick, etc. will hurt head retention. If the glass is very warm, the beer will foam up. Frosted glasses also cause foaming. Refrigerated glasses minimize foaming.

Medicinal, plastic, Band-Aid: Phenolic compounds from 1) chlorine, or 2) mashing/sparging with improper temperature, pH, or amount of sparge water. Aromatic hydrocarbons from wild yeasts or coliform bacteria.

Sour/acidic: Lactic acid (several kinds of bacteria, most likely Lactobacillus). Butyric acid (Clostridium). Acetic acid (several kinds of bacteria, as well as Brettanomyces). Pyruvic acid (made by most organisms during glycolysis).

Butyric acid (CH₃CH₂CH₂COOH), found in rancid butter and vomit, is detected by humans above 10ppm, and by dogs at 10ppb. It is thrown out of its aqueous solution by the addition of calcium chloride.

Some acetic acid bacteria leave a film on top of wort.

Sulfur (rotten eggs): Wild yeast and bacteria (e.g. Zymononas, Pectinatus, Megasphaera). Yeast autolysis.

Green apple: Acetaldehyde from oxidized ethanol. Acetic acid from bacteria or oxidized acetaldehyde. Yeast activity ending before converting acetaldehyde to alcohol.

Astringent: Compounds produced by bacteria or wild yeast, e.g. lactic acid from Lactobacillus or acetic acid from Acetobacter. Polyphenols from boiled/oversparged grain husks, boiled fruit skins, excessive trub, or excessive hopping (hop oils can be converted to polyphenolic anthocyanogens). Alkaline or high-sulfate water.

Solventy/acetone: Esters such as ethyl acetate and isoamyl acetate, resulting from high fermentation temperatures, high-gravity worts, low pitching rates, long periods in contact with trub, or wild yeasts.

Grassy: Oxidation products of humulene in old hops. An aldehyde called cis-3-hexenol, formed in improperly stored malt.

Cooked vegetable: Bacteria. Sulfur compounds such as diethyl sulfide, dimethyl sulfide and di-isopropyl sulfide produced from malt precursors during the wort boil and cooling. Improperly stored malt. Short boiling time. Long cooling time.

Papery: Staling aldehydes, mostly trans-2-nonenal, formed from the oxidation of higher alcohols or hop lipids. Carbonyl compounds formed from the oxidation of fatty acids.

Metallic: Iron. Freshly scrubbed stainless steel that hasn't had a chance to oxidize. Fatty acid oxidation.

Malt sugar is typically:

Fructose, which is also found in fruit and honey, is the sweetest sugar, followed by sucrose, glucose, maltose, and maltotriose. The more glucoses in a molecule, the less sweet it is. Corn sugar is glucose.

Molasses is sucrose (40-50%), invert sugars and dextrins. It's about 90% fermentable.

Honey, which is about 95% fermentable, is typically 38% fructose (27-45% range), 31% glucose (23-41%), 8% disaccharides (3.6-16%), 1% sucrose (0-6.5%), 3% dextrins (0-8.5%), and 18% water (13-23%). It also contains amylase, wild yeast and bacteria.

Belgian candi sugar is simply caramelized sucrose. Except for the caramel notes, it is exactly the same as sucrose (table sugar). Sucrose comes from sugar cane, beets, maple sap, and nectar.

Sucrose and candi sugar have a PPG of 46. Corn sugar has a PPG of 42.

Witbiers are often flavored with curacao orange (the flavoring used in Triple Sec). I've found that store-bought orange peels work.

Sodium at 75-150 ppm can give round smoothness, but combined with sulfate can give harshness. If adding salt to wort, use CaCl₂ rather than CaSO₄ in the mash. One tsp (5.3g) NaCl adds 110 ppm Na and 170 ppm Cl to five gallons of wort. Use only noniodized salt because iodine can impede yeast function.

All recipes are for 5 gallons, and are to be used as general guidelines only. Grain amounts needed for target gravities will vary depending on the type(s) of grain used (European grains tend to yield more than American grains) and the efficiency of the lauter system. Clone recipes are little more than best guess, consensus among homebrewers, and trial & error. Hop amounts are not always given - they are to be adjusted for preference. Styrian Goldings, used in many Belgian beers, is a Fuggle hop grown in Slovenia, so Fuggles can be substituted. All recipes can benefit from calcium chloride or gypsum. Mash schedules are single infusion except where noted, but a protein rest should be considered if using pils malt.

Bos Keun
pale malt, 2# sugar
7 AAUs Styrian Goldings
Saaz - aroma
grains of paradise?
Bos Keun yeast or Wyeast 3942
OG=78-81
ferment at 70-73º

Chimay
66% barley, 22% wheat, 12% sugar
6-12 AAUs Styrian Goldings (Chimay White has more AAUs than Red/Blue)
Hallertau - flavor
1-2 tbsp molasses
4-16 ozs honey
Chimay yeast
OG=63 (Red), 71 (White), 81 (Blue)

Duvel
pils/pale malt
3# sugar
10-11 AAUs Styrian Goldings 90 minutes
1 oz Saaz 15 minutes
0.5 oz Styrian Goldings 5 minutes
Duvel yeast or Wyeast 1388
cold store around 35º for 3 weeks before bottling
refrigerate 2-3 months before drinking
OG=80

Lindeman's Framboise
50-70% pils, 30-50% flaked or unmalted wheat
step mash at 95º, 113º, 130º, 149º, 158º
4 AAUs aged Saaz
OG=61-63; primary fermentation with Wyeast 1056
secondary:

46 ozs Oregon seedless raspberry concentrate
20 drops pectin enzyme
Wyeast 3278 lambic blend *

* Use Brettanomyces lambicus, Brettanomyces bruxellensis and Lactobacillus. Brettanomyces produces the volatile phenolic compounds 4-ethyl-phenol and 4-ethyl-guaiacol. Lactobacillus produces lactic acid, which is esterified into ethyl lactate, which gives lambics their distinctive aroma.

Mad Bitch (Dulle Teve)
pale malt
sugar?
Styrian Goldings
Wyeast 3942
OG=80-85

Orval
86.5% pale malt
13.5% 50L crystal
1# sugar
mash: 145º, then 160º for 60 minutes
boil 20 minutes before adding hops
5-8 AAUs Styrian Goldings pellets
Hallertau - flavor
dry hop with whole Hallertau
Orval yeast or Chico / Brettanomyces bruxellensis combo
OG=55-60
start fermentation at 59º, allow to rise no higher than 74º

Pale Ale
11-12# pale
0.5# 20L crystal
0.2# carapils
7-9 AAUs Northern Brewer
1 oz Cascade - flavor
2 ozs Mt. Hood - aroma
Wyeast 1056 or White Labs WLP001
OG=56

Petrus Triple
pale, caravienne
1.5# sugar
7.5 AAUs Styrian Goldings
Styrian Goldings, sweet orange peel 15 min
Willamette, sweet orange peel 3 min
Wyeast 3787
OG=75
secondary: 4 ozs oak chips

Rulles Triple
pale + pils
1.5 - 2# sugar
7-8 AAUs Styrian Goldings
1 oz Hallertau, Saaz or East Kent Goldings - aroma
Rulles yeast
OG=73
ferment at 72º
This yeast ferments slowly so it might take a month or two.

Saison Dupont
pils/pale/wheat
ferulic acid rest
protein rest
1# sugar
5-7 AAUs Saaz or Styrian Goldings
East Kent Goldings or Hallertau - aroma
Saison Dupont yeast or White Labs WLP565
OG=63
ferment at 80-90º
Allow to ferment for several weeks because this yeast takes a while to eat the last of the sugars.

Tuppers Hop Pocket Ale
12# pale
all hops are whole
8-9 AAUs Columbus
2 ozs Cascade - 20 minutes
1 oz Liberty - 10 minutes
1 oz Cascade - aroma
1 oz Mt. Hood - aroma
dry hop with 2 ozs Cascade and 2 ozs Mt. Hood for 3 weeks
Wyeast 1056 or White Labs WLP001
OG=55

Westmalle Triple
pale/pils
2# sugar
8-11 AAUs Styrian Goldings
Fuggles, Saaz or Hallertau - aroma
dry hop with Hallertau
Wyeast 3787 or Westmalle yeast
OG=80
ferment at 64-68º

Witbier
5.5# pils
5.5# flaked or malted wheat
rice hulls
ferulic acid rest
protein rest
5 AAUs
5-6 orange peels (5-10 minutes)
2 tbsp coriander powder (5-10 minutes)
White Labs WLP400
OG=55
ferment at 75º