The brewer’s mash is the last step of many taken, prior to lautering, to produce wort from starch. The process begins in the malt house where barley is germinated and then dried. Malting gives the grain a rich complement of enzymes that are stabilized by kilning. Brewers must control these enzymes during mashing to produce a wort with specific features.
On the surface the brewery mash appears to be a simple mixture of malt and water. When held hot for a period the mash begins to thin, producing a cloudy, semi-sweet liquid, then transforming into a mixture of clear, intensely sweet wort and spent grains.
Beyond these macroscopic changes lie important biochemical reactions that convert the starch found in the grain into sugar. Malt enzymes act as catalysts, in a sense causing these reactions.
Mashing begins when malt solids dissolve. These solids are primarily made up of starch but also include a significant portion of proteins. Included among the proteins are the catalysts, malt enzymes. The enzymes latch onto mainly starch and smaller carbohydrate molecule chains in a mash, bringing about a chemical reaction. These starch and carbohydrates are called substrates, because they are broken down by the protein-based enzymes during the reaction.
Smaller proteins, smaller beta-glucans (viscous gums that contribute to wort viscosity), sugars, and dextrins (unfermentable carbohydrates that add body to beer) are the products of enymatic attack and their parent compounds — proteins, beta-glucans, and starch — are called enzyme substrates.
The brewer’s challenge is to let nature travel its free-wheeling road but in a controlled environment.
Mash temperature, mash pH, water chemistry, enzyme concentration, substrate concentration, and product concentration are the mash variables that can be easily controlled.
Mash temperature has a great influence on which enzymes are active, because enzyme activity depends on temperature. Temperature also can cause enzymes to denature and permanently lose their catalytic activity. The principle enzymes involved in mashing all have different optimal temperatures.
Like temperature, mash pH affects enzyme activity. Enzymes must be in specific pH ranges to be active catalysts. In general the mash pH should fall between 5.2 and 5.4, because the enzymes of interest to brewers are active in this range. With most brewing waters and malts mash pH naturally falls in this range, so pH is not one of the mash variables that demands vigilant monitoring.
Other attributes that affect enzyme action are the concentrations of enzymes, substrates, and their products. These features are very important, because they influence the rate at which starch is broken down in the mash. As this reaction proceeds, the concentration of products (such as smaller carbohydrates) begins to build up and can slow down the reactions occurring in the mash. In addition to the speed or rate of the reaction, concentration can affect enzyme stability.
What Does It All Mean?
The concentration of enzyme, substrate, and product fall under the umbrella of “mash thickness.” Mash thickness is the weight ratio of water in the mash to malt in the mash.
Since one liter of water weighs one kilogram, mash thickness is easily determined when malt is measured in kilograms and water is measured in liters. For example, if 12 liters of water go into a mash with four kilograms of malt, the mash thickness — or if you are British, the liquor to grist ratio — is 3:1. Although this is the most common way of expressing mash thickness, some brewers use the ratio of malt to water and express the ratio as a percentage. In the previous example the mash thickness could also be called 33 percent malt. In both cases it is simply the weight ratio of water to malt.
Although there are infinite mash thicknesses to use in brewing, three generic ranges of thickness are used in practice. These are the “thick mash,” the “medium-thick mash,” and the “thin mash.” These terms do not define thickness in absolute terms, but they do convey some important messages to the brewer.
The Thick Mash
In a thick mash the concentrations of enzymes, substrates, and products are all high, since there is a bunch of malt in a little bit of water. In numerical terms a thick mash is anything less than about 2.5 parts water to one part malt. The rule of thumb for mash thickness quoted in many homebrewing books is one quart of water per pound of malt; as a weight ratio that is 2.1:1. That is a pretty darn thick mash!
The thick mash has certain ramifications. The most striking feature is that it provides substantial protection to the enzymes present in the mash. In other words the enzymes are less likely to be denatured (stripped of qualities that allow it to catalyze the desired reaction) by high temperatures. This feature allows beta-amylase and alpha-amylase to work in concert, which is handy for a single-temperature mash. Without the protection of the thick mash, beta-amylase could be quickly denatured and the resulting wort would be predominated by the products of alpha-amylase action. Such a wort would have a high concentration of unfermentable carbohydrates. The resulting beer would have a higher terminal gravity and lower alcohol content than a beer made from a more fermentable wort.
On the Other Hand
Thick mashes do have obvious advantages, but there are some problems. Water is required to break down starch. Water is chemically inserted between the glucose molecules of the starch polymer during hydrolysis (the enzyme-directed breakdown of starch) and a shortage of water can cause incomplete breakdown of starch during mashing. Although mashes are rarely thick enough to cause incomplete starch conversion, very thick mashes can slightly decrease wort fermentability.
A less subtle result of thick mashes is noticeably lower extract yield. Thick mashes simply cannot bring all of the malt starch into solution. Although decreased extract yield is not going to send any homebrewer to the poor house, commercial brewers are not very fond of this side of the thick mash.
The last major problem with thick mashes is the high concentration of starch breakdown products. This feature is easy to spot when the specific gravity of the first runnings from the mash is taken. In thick mashes the first running gravity is usually greater than 20˚ Plato (1.078). These products can interfere with enzyme action, resulting in what is called product inhibition.
Product inhibition may serve to control the millions of enzymatic reactions occurring every second in the human body, but it is not the brewer’s best friend. In the mash, product inhibition can lead to incomplete starch breakdown and decreased extract yield and fermentability.
Some enzymes, especially proteases (enzymes that attack protein), are very sensitive to product inhibition and are not very active in such environments. Periodically stirring a thick mash can help to alleviate product inhibition, since stirring distributes the enzymatic products that naturally accumulate near enzymes.
If a mash thickness less than 2.5:1 is thick, then a mash thickness between 2.5:1 and 4:1 should be medium. In practice a thickness of about 3.25:1 best captures the feel of the medium-thick mash. These mashes retain many advantages of the thick mash but few of the downsides. Additionally, mashes in this range of stiffness are easy to move around. This feature is important when conducting stirred, multi-temperature mashes as it allows for easier mixing and better heat transfer than a thick mash. These mashes are easy to pump, if required. Commercial breweries, for example, pump the mash from the mash vessel to the lauter tun.
Although thinning out the mash makes the enzymes less concentrated and hence more susceptible to temperature denaturation, this only occurs if the mash is conducted at an unacceptably high temperature. In general an infusion mash temperature of 150° to 155˚ F in a medium-thick mash allows sufficient beta-amylase activity before rendering it inactive (beta-amylase usually begins losing activity above 149° F).
After beta-amylase is denatured, alpha-amylase remains active because it is less sensitive to these temperatures, it can survive up to 170° F. If multi-temperature mashing is used, then these problems are alleviated, regardless of thickness. But the thinner mash makes stirring easier.
The thinner mash also decreases the concentration of substrates and products. This minimizes the effects of product inhibition, the slowing of chemcial reactions caused by build-up, and also eliminates the loss of extract associated with very thick mashes.
In general the medium-thick mash provides for good enzyme activity, allows for easy stirring and pumping, will produce a wort with a high degree of fermentability, and produces a good extract yield from the malt. However, if a mistake is made by mashing in too hot, then the chance of causing irreversible enzyme loss is higher than if the same mistake is made in a thick mash.
Thin mashes are any mashes where the water-to-malt ratio exceeds 4:1. Like the medium-thick mashes, thin mashes are easy to move around and provide excellent heat transfer. They also give high extract yields, since the malt solids are easily dissolved.
The problem with thin mashes is enzyme stability. Enzymes are less stable in a thin mash and denaturation can become a real problem. The enzyme of concern is beta-amylase, since there is a limiting supply of beta-amylase in comparison to alpha-amylase. If beta-amylase denatures too quickly, then the resulting wort will have a decreased fermentability.
Some multi-temperature mash schedules suggest adding very hot water to increase temperature. This technique thins the mash and can render enzymes, especially beta-amylase, inactive when they are most needed. You may not like this method unless you want to limit fermentability.
Into The Thick Of It
It may seem like the logical conclusion is to only use thick and medium-thick mashes. But for some special cases thin mashes may do just the trick. Suppose the goal is to produce a wort with good extract yield and a negative iodine reaction but with low fermentability (such as a low-alcohol beer).
Some brewers try to accomplish this goal by mashing at a very high temperature in hopes of killing off most of the beta-amylase before producing much maltose. In thick and medium-thick mashes, high temperatures are not as destructive as may be expected. Most of the so-called optimum temperatures for enzymes are for model systems carried out in laboratories. Since these temperatures are usually not representative of mashing conditions, exceeding text book numbers does not always do the trick.
This is where varying mash thickness becomes an effective method of wielding control over the mash. To limit fermentability, a thin mash coupled with high temperatures (say 160˚F) may be more effective than mashing at 170˚ F in a very thick mash.
This topic has become of interest to many commercial brewers in recent years who have taken an interest in low- and non-alcohol beers. Although homebrewers are usually not looking to produce bland, low-alcohol products, some are dabbling with full-flavored but low-alcohol beers such as some mild ales. If these beers have tickled your taste buds, then mash thickness control may be the parameter you’ve been looking for to brew low-alcohol beers without sacrificing body.
The next time you’re mashing, consider mash thickness in addition to temperature and pH as one of the parameters that sets the stage for the dance of the enzymes.