by David Houseman and Scott Bickham
The primary goal of mashing is to complete the breakdown of proteins and starches that was begun during the malting process. This is accomplished by several groups of enzymes that degrade different substrates during a series of rests at specific temperatures.
With pale lager malts, this enzymatic degradation begins with the acid rest, where phytase breaks down phytin into calcium- and magnesium-phosphate and phytic acid. This helps acidify the mash when the brewing water has low calcium content and roasted grains are not part of the grist. This rest occurs at temperatures in the 95-120 °F (35-50 °C) range. Another group of active enzymes in this range are the b-glucanases, which break down hemicellulose and gums in the cell walls of undermodified malts. Some adjuncts, particularly rye, have high levels of these substances, and stuck mashes or other problems can result if they are not degraded to simpler substances by the b-glucanases.
For most malts, the mash begins with the protein rest, which is normally carried out at temperatures in the 113-127 °F (45-53 °C) range. This process begins with the proteinases, which break down high molecular weight proteins into smaller fractions such as polypeptides. These polypeptides are further degraded by peptidase enzymes into peptides and amino acids, which are essential for proper yeast growth and development. Proteins of molecular weight 17,000 to 150,000 must be reduced to polypeptides of molecular weight 500-12,000 for good head formation, and some of these further reduced to the 400-1500 level for proper yeast nutrition.
The final enzymatic process involves the conversion of starches into dextrins and fermentable sugars. The starches must be gelatinized for this to take place, and this occurs at temperatures of 130-150 °F (55-65 °C) for barley malt. The gelatinization temperature is higher for raw grains, such as corn grits, so these adjuncts must be boiled or hot-flaked before adding to the mash. The breakdown of starches is carried out by the combined action of debranching, a-amylase and b-amylase enzymes during the saccharification rest. Debranching enzymes break the 1-6 links in starches, reducing the average length and complexity of the molecules. The diastatic, or amylase, enzymes work in tandem, with the b-fraction breaking off maltose units from reducing ends and the a-fraction breaking 1-4 links at random. Temperatures below 150 °F (65 °C) favor b-amylase, producing a more fermentable wort, while temperatures above 155 °F (68 °C) favor a-amylase, producing a more dextrinous wort.
The simplest sugars produced in the above manner are monosaccharides, with only one basic sugar structure in the molecule. Monosaccharides in wort include glucose, fructose, mannose and galactose. Disaccharides are made up of two monosaccharides coupled together, and include maltose, isomaltose, glucose, melibiose, and lactose. Trisaccharides (three monosaccharides) include maltotriose, which is slowly fermentable and sustains the yeast during lagering. Oligosaccharides constructed of glucose chains (many monosaccharides joined together), are water soluble and called dextrins. The relative concentrations of these sugars are determined by the types of malt and whether the mash schedule favors a-amylase or b-amylase activity.
After this phase is completed, many brewers mash-out by raising the temperature of the mash to 168 °F (76 °C) and holding it there for several minutes. This ensures the deactivation of the amylase enzymes, halting the conversion of dextrins to fermentable sugars. It also reduces the viscosity of the wort, helping to make the lautering easier and more efficient. There is some controversy whether this step is necessary depending on the final mash temperature. However, it is generally agreed that the best extraction rates are achieved when the mash is heated to this range.
The mashing process begins by doughing-in the crushed grains with approximately 1-2 liters of water per pound of grain (2-4 liters per kilogram). The starch granules take up water with the aid of liquefaction enzymes, and the rests described above are carried out according to the degree of modification of the malt. The simplest mashing method is the single-step infusion, where the malt is combined with hot water to reach a temperature appropriate for starch conversion. This is the method of choice for fully-modified malts such as those used to brew British ales. It has the advantage of requiring a minimum of labor, equipment, energy and time, but prohibits the use of undermodified malt or adjuncts. A step-infusion mash allows a little more flexibility by moving the mash through a series of temperature rests. The temperature is increased by external heat or the addition of boiling water. This requires more resources than a simple infusion mash, but undermodified malts may be used.
Decoction mashing involves the removal of a thick fraction of the mash (usually one-third) and running it through a brief saccharification rest at a relatively high temperature. It is then boiled it for 15-30 minutes before mixing it back into the main mash. This is repeated as many as three times, depending on the modification of the malt and the beer style. The decoction helps explode starch granules and break down the protein matrix in undermodified malt, improving the extraction efficiency, and also promotes the formation of melanoidins. These compounds are formed from amino acids and reducing sugars in the presence of heat and are responsible for the rich flavors in malty lagers. This mashing method is the most resource intensive, but is the traditional method for many lagers. A possible side-effect of the extended mash schedule is the extraction of higher levels of tannins and DMS precursors from the grain husks, though this is not significant at typical mash pH levels.
A fourth mashing method is the double mash, which can be viewed as a combination of infusion and decoction. As the name implies, it involves two separate mashes: a main mash consisting of crushed malt, and a cereal mash consisting of raw adjuncts and a small charge of crushed malt. The latter is boiled for at least an hour to gelatinize the starches and is then added to the main mash, which has undergone an acid rest. The mixture is then cycled through protein and saccharification rests using the step-infusion method. The double mash is the most common way of producing beer styles such as American light lagers that contain a high proportion of corn grits or rice.
Lautering is the process of separating the sweet wort from the grain fractions of the mash. It is usually done in a vessel—appropriately called a lauter tun—that holds the grain and wort with some form of strainer in the bottom to separate the liquid wort from the grain. In most homebrewing setups, the mash tun, where the mash process occurs, and the lauter tun are the same unit. Where the brewer chooses to utilize two vessels and convey the mash contents from the mash tun to a special purpose lauter tun care must be taken to not introduce oxygen into the hot wort. This hot side aeration can introduce oxidative off flavors the finished beer that are often perceived as sherry-like, wet paper or cardboard-like.
Lautering consists of draining the wort off the grain and sparging, or the addition of hot liquor (treated brewing water) to the top of the grain bed to rinse the sugars from the grain. This procedure should be done slowly, with the wort returned to the tun until the run-off is clear. This initial runoff and return of wort to the lauter tun is called a vorlauf and is critical to preventing astringency and haze in the finished beer. Lautering too fast will give poor yield, poor extraction rates, and possibly flush starch and protein fractions into the wort. Failing to re-circulate the initial runoff through the lauter tun until it is reasonably clear will have a similar effect.
A temperature range of 160-170 °F (70-77 °C) should be maintained throughout the entire process; this ensures that the greatest extraction of sugars from the grain without excess tannin extraction from the husks. Temperatures above 170 °F (77 °C) will leach tannins and permit undissolved starch balls to explode and get past the filterbed, and gums and proteins may also be released into the wort. This starch will pass on to the finished beer without being fermented until broken down over a period of time by wild yeast or bacteria present.
Another potential problem is a stuck sparge, which may be caused by an inadequate amount of filtering material in the grain bed—usually barley husks—that allow wort to pass freely while holding back the bits of material to be filtered. When mashing with high quantities of wheat or rye malt that will not have their own husks to aid as a filter, it’s usually necessary to add additional filter material such as rice hulls, which themselves are neutral to the flavor or gravity of the resulting beer. Wheat, rye, oats and some other cereal grains also contribute a much higher proportion of gums that can help cause a stuck mash. These often require a b-glucanase rest in order to break down these gums and aid the resulting sparge.
Sparging is the addition of rinse water, or hot liquor, to the lauter tun. In general, the water chemistry of the sparge water should match that used in mashing. The pH should be approximately 5.7 in order to prevent the mash pH from exceeding 6.0, which promotes the extraction of excess tannins.
The sparge rate should be slow, with the water (at 170 °F, 77 °C) added gently so that the filter bed is not disturbed. A hydrometer reading of the first runs from the tun should be about twice the value desired in the finished beer. If not, it should be returned to the tun. Sparging should cease when the gravity drops to below about 1.010 or the pH of the runoff increases above 6.0. Monitoring of the runoff is essential in order to stop the collection of wort before excess tannins are extracted. Learning to taste the sweet wort to recognize when to stop the collection will provide the brewer with an intimacy of the process that doesn’t require the use of the hydrometer or pH meters and papers.
Boiling wort is normally required for the following reasons:
- Extracts, isomerizes and dissolves the hop a-acids
- Stops enzymatic activity
- Kills bacteria, fungi, and wild yeast
- Coagulates undesired proteins and polyphenols in the hot break
- Evaporates undesirable harsh hop oils, sulfur compounds, ketones, and esters.
- Promotes the formation of melanoidins and caramelizes some of the wort sugars (although this is not desirable in all styles)
- Evaporates water vapor, condensing the wort to the proper volume and gravity (this is not a primary reason, it’s a side effect of the process)
A minimum of a one hour boil is usually recommended for making quality beer. When making all grain beer, a boil of 90 minutes is normal, with the bittering hops added for the last hour. One exception to boiling was historically used to brew the Berliner Weisse style. Here, the hops were added to the mash tun, and the wort is cooled after sparging and then fermented with a combination of lactobacillus from the malt and an ale yeast.
Boiling for less than one hour risks under-utilization of hop acids, so the bitterness level may be lower than expected. In addition, the head may not be as well formed due to improper extraction of isohumulones from the hops. A good rolling boil for one hour is necessary to bind hop compounds to polypeptides, forming colloids that remain in the beer and help form a good stable head. An open, rolling boil aids in the removal of undesired volatile compounds, such as some harsh hop compounds, esters, and sulfur compounds. It is important to boil wort uncovered so that these substances do not condense back into the wort.
Clarity will be also be affected by not using at least a full hour rolling boil, as there will not be a adequate hot break to remove the undesired proteins. This will also affect shelf life of the bottled beer, since the proteins will over time promote bacterial growth even in properly sanitized beer bottles. The preservative qualities of hops will also suffer greatly if the wort is not boiled for one hour, as the extraction of the needed compounds will be impaired.
Boiling wort will also lower the pH of the wort slightly. Having the proper pH to begin the boil is not normally a problem, but if it is below 5.2, protein precipitation will be retarded and carbonate salt should be used to increase the alkalinity. The pH will drop during the boil and at the conclusion should be 5.2-5.5 in order for proper cold break to form and fermentation to proceed normally. Incorrect wort pH during the boil may result in clarity or fermentation problems.
The effects of boiling on the wort should match the intended style. It is often desirable to form melanoidins which are compounds produced by heat acting on amino acids and sugars. These add a darker color and a maltier flavor to beer. When desired, an insufficient boil will not form enough melanoidins for the style. Boiling the initial runnings of high gravity wort will quickly caramelize the sugars in the wort. This is desired in Scottish ales, but would be inappropriate in light lagers.
Vigorously boiling wort uncovered will evaporate water from the wort at a rate of about one gallon (four liters) per hour, depending the brewing setup. In order to create a beer with the appropriate target original gravity, changes in the wort volume must be taken into account. Longer boil times or additions of sterilized water may be required to hit the target gravity.
After boiling for a sufficient amount of time, the wort should be chilled at rapidly as possible, using either an immersion or counter-flow system. This minimizes the risk of contamination by Lactobacillus or wort-spoilage bacteria and produces an adequate cold break. This cold break consists of protein-protein and protein-polyphenol complexes and is often promoted by the addition of Irish Moss or Whirlfloc tablets to the kettle near the end of the boil. There is some debate on whether the cold break should be completely removed. On one hand, it can provide carbon skeletons that can be used by the yeast for sterol synthesis, but on the other, excessive levels may lead to elevated levels of esters and fusel alcohols and promote the formation of chill or permanent haze in the finished beer.
Irish Moss and Whirlfloc tablets are categorized as kettle fining agents since they are added during the last 10-15 minutes of the boil to aid in in coagulation and precipitation of proteins during the cold break. Irish moss is a dried form of a red seaweed variety that grows along the rocky Atlantic coastlines of Europe and North America. Whirlfloc tablets are also derived from seaweed, but with an enhanced flocculation ability due to the addition of purified carrageenan, which is the active ingredient in Irish Moss.
Fining agents can also be added at the end of fermentation to promote the sedimentation of residual protein-polyphenol complexes or yeast. These include silica hydrogels, gelatin, isinglass and polyclar. Gelatin and isinglass are collagen-based agents derived from animal hooves and fish bladders, respectively. They are used by dissolving small quantities in hot (but not boiling) water and adding the solution to the fermenter a few days prior to racking or bottling. Polyclar is a powdered plastic material with positively charged molecules that attach to the negatively-charged protein-polyphenol molecules to form larger aggregates that sink to the bottom of the fermenter.
- Dave Miller, Dave Miller’s Homebrewing Guide (Garden Way Publishing, Pownal, VT 1996).
- Darryl Richman, Bock (Brewers Publications, Boulder, CO, 1994).
- Gregory J. Noonan, New Brewing Lager Beer (Brewers Publications, Boulder, CO, 1996).
- George Fix, Principles of Brewing Science (Brewers Publications, Boulder, CO, 1989).
- George and Laurie Fix, An Analysis of Brewing Techniques (Brewers Publications, Boulder, CO, 1997)