The process of making beer wort (unfermented beer) encompasses several steps. The first of these is mashing.
The primary goal of mashing is to finish the breakdown of proteins and starches that the maltster began when he produced the malt.
In days past, when malts
were less modified, the mashing process was accomplished by using
several steps that utilized various groups of enzymes to degrade
different parts of the proteins during a series of rests within a
specified range of temperatures.
Before the chemistry behind the interaction of malts and water was well understood, brewers in certain areas, namely Pilzen, had a difficult time getting their mash pH to reach the proper range when using only pale malts.
The darker grains, and especially the highly kilned malts, acidify the mash and brewers using these malts do not have the problems with mash pH that those in Pilsen had.
Pilzen's water was so soft and devoid of minerals that they had to employ a special mash rest within the temperature range of 86°-126°F (30°-52°C) to acidify the mash to prevent the beer from getting overly astringent.
Most malts today are well modified and don't require an acid rest, thus it is rarely used anymore.
The reaction of the malt's phytase enzyme breaks down the phytin in pale lager malts into calcium and magnesium phosphates and phytic acid.
By removing the ion buffers and producing a weak acid, phytic acid, the mash pH is lowered. Today through the use of the proper mineral additions, proper mash pH can be achieved without an acid rest.
About the only time one might want to employ this mash is when using a large percentage of brewing adjuncts which have high levels of hemicellulose and gums in their cell walls.
The enzyme beta glucanase works in this temperature range to break down these substances to help prevent stuck mashes or other problems when a large percentage of rye is used in the grist.
The next step in the mashing regime is called the protein rest. It is employed for undermodified malts which may still be purchased from German maltsters.
These moderately-modified malts benefit from a protein rest in the range of 113°-131°F (45°-55°C) to break down any remaining large proteins into smaller proteins and amino acids. Some brewers feel that they get a fuller and maltier flavor profile by using a protein rest on less modified malts.
Malted barley has many amino acid chains which were in place for the germinating plant. They are now used by the yeast for their growth. The two main enzymes responsible for protein degradation are peptidase and protease.
It is peptidase which provides the wort with the amino acid nutrients used by the yeast.
Protease breaks down the larger proteins which help enhance head retention and reduce haze.
For most of us that use well modified malts, the work of the two proteolytic enzymes has already been completed during malt production. In fact, you don't want to do a protein rest with well modified malts because of the breakdown of the proteins which produce body and head retention. The resulting beer would be thin and watery.
However, when using a grist with >25% of unmalted grains like flaked wheat, rye, oatmeal or barley, employing this rest will break up the beta-glucans which, if left intact, may cause a gummy mess and stuck mash.
The enzymes which accomplish this are the beta-glucanases and beta-cytases. Fortunately for the homebrewer, these enzymes have an optimum temperature which is below that used by the proteolytic enzymes, allowing us to rest in the 98°-113°F (37°-45°C) range without affecting those proteins we need for body and head retention.
When using less than 25% unmalted grains, utilizing a mashout will aid in solubilizing the gums prior to running off into the wort.
For most of the homebrewers in the world, the only rest we use is the saccharification rest which gelatinizes and then converts the starches into dextrins and fermentable sugar.
The gelatinization (or the "melting" of the bonds in a starch's crystalline structure) temperature for starches in our mash is in the 130-150° (54°-66°C) range for barley malt.
When using raw grains such as corn grits, the gelatinization temperatures are higher and thus they must be boiled in a separate cereal mash prior to being added to the mash.
The amylases, alpha and beta, work by hydrolyzing the straight chain bonds between the glucose molecules in the starch chain.
One single starch chain is called an amylose (about 25% of the barley malt starch is amylose) and a branched chain (made up of amylose chains) is called an amylopectin (which makes up the other 75% of the starch in barley malt). Both enzymes, beta-amylase and alpha-amylase, attack the starch, but do so in different ways.
Alpha-amylase chops up starch molecules randomly into chunks that beta-amylase can then work on. Until these molecules are chopped up, they are unfermentable and called dextrins.
What alpha-amylase does is called liquefication. It physically liquefies the starches, making them ready for further enzymatic activity. Mash schedules that target the alpha-amylase enzymatic action (optimum at 158°F/50°C) yields a wort with a high percentage of unfermentable sugars, or dextrins. The beer produced is very rich, with a thicker body and mouthfeel.
Beta-amylase breaks down starch and dextrins into glucose (one molecule), maltose (two molecules) and maltotriose (three molecules). After beta-amylase is through working, the starch has been broken down into fermentable sugar.
Mash schedules that target the beta-amylase enzymatic action (optimum at 140°-149°F/60°-65°C) yield a wort that is highly fermentable. The beer produced will be drier tasting and contain more alcohol.
Customize Fermentability of Your Beer by Adjusting Mash Temperature
What this knowledge means to homebrewers is that they can customize the fermentability and body of their beers by adjusting the mash temperature, and thus the enzymatic activity.
It is important to understand that although mash enzymes have an optimum temperature, they will work over a wide range, and most of the time, the activity of enzymes overlap within that range.
Both alpha-amylase and beta-amylase will work well together within the range of 145° to 158°F (63°-70°C). So in general, if you want a thinner, drier, more alcoholic beer you can mash in the lower portion of this range, and if you want a richer more dextrinous beer with more mouthfeel and body, you should mash in the upper portion of this range. A good compromise is made by mashing in the middle, around 152°F (67°C).
Adjusting Mash Thickness
Another variable homebrewers can affect is mash thickness. A thick mash (which has a lower water / grain ratio) will keep the enzymes in contact with the starches and allow them work better and quicker.
A thick mash, <1.25 qts. of water/pound of malt, is better at breaking down proteins and results in a faster starch conversion. But, the sugars that result will be less fermentable and the beer will be taste sweeter and maltier.
It should be noted that a thick mash is easier on the enzymes because heat transfers less in grain than in water. The result is that the enzymes are protected from the denaturing effects of high temperatures in a thick mash.
For the homebrewer, using a thicker mash will allow the beta and alpha-amalyse enzymes to work in concert when using a single infusion mash at higher temperatures.
A thin mash, >2.0 qts. of water / pound of malt, dilutes the relative concentration of enzymes in the mash. Thin mashes are much easier to move around, have a better heat transfer, and produce a better yield since the starches are more easily dissolved.
One problem with a thin mash is the stability of the enzymes. They are more prone to the denaturing effects of higher temperatures. If the beta-amalyse enzyme denatures too quickly, the resulting beer will be less fermentable.
A thin mash will slow down starch conversion but ultimately produces a more fermentable, thinner and drier, beer because the enzymes are not inhibited by the increased concentration of sugars in the wort.
For a more detailed look at enzyme activity in brewing, go the the enzymes page on my website.
References: Information for this page on wort production was adapted from How to Brew by John Palmer, the article what mash temperatures create a sweet or dry beer? by Aston Lewis appearing in BYO magazine in the June 1999 issue, and the article Wort Production by David Houseman and Scott Bickham in the BJCP Beer Exam Study Guide.
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