Mashing is the brewer's term for the hot water steeping process which hydrates the barley, activates the malt enzymes, and converts the grain starches into fermentable sugars. There are several key enzyme groups that take part in the conversion of the grain starches to sugars. During malting, the debranching (chainsaw), beta-glucanase (weed whacker) and proteolytic (lawnmower) enzymes do their work, preparing the starches for easy access and conversion to sugars. During the mash, a limited amount of further modification can be accomplished, but the main event is the conversion of starch molecules into fermentable sugars and unfermentable dextrins by the diastatic enzymes (hedge trimmer and clippers). Each of these enzyme groups is favored by different temperature and pH conditions. A brewer can adjust the mash temperature to favor each successive enzyme's function and thereby customize the wort to their taste and purpose.
The starches in the mash are about 90% soluble at 130 °F and reach maximum solubility at 149°F. Both malted and unmalted grains have their starch reserves locked in a protein/carbohydrate matrix which prevents the enzymes from being able to physically contact the starches for conversion. Unmalted grain starch is more locked-up than malted. Crushing or rolling the grain helps to hydrate the starches during the mash. Once hydrated, the starches can be gelatinized (made soluble) by heat alone or by a combination of heat and enzyme action. Either way, an enzymatic mash is needed to convert the soluble starches to fermentable sugars.
Figure 79 - Typical Enzyme Ranges in the Mash
Table 11 - Major Enzyme Groups and Functions
| Enzyme | Optimum Temperature Range | Working pH Range | Function |
| Phytase | 86-126°F | 5.0-5.5 | Lowers the mash pH. No longer used. |
| Debranching (var.) | 95-113°F | 5.0-5.8 | Solubilization of starches. |
| Beta Glucanase | 95-113°F | 4.5-5.5 | Best gum breaking rest. |
| Peptidase | 113-131°F | 4.6-5.3 | Produces Free Amino Nitrogen (FAN). |
| Protease | 113-131°F | 4.6-5.3 | Breaks up large proteins that form haze. |
| Beta Amylase | 131-150°F | 5.0-5.5 | Produces maltose. |
| Alpha Amylase | 154-162°F | 5.3-5.7 | Produces a variety of sugars, including maltose. |
Note: The above numbers were averaged from several sources and should be interpreted as typical optimum activity ranges. The enzymes will be active outside the indicated ranges but will be destroyed as the temperature increases above each range.
The Acid Rest and Modification
Before the turn of the (last) century, when the interaction of malt and water chemistry was not well understood, brewers in Pilsen used the temperature range of 86-126°F to help the enzyme phytase acidify their mash when using only pale malts. The water in the area is so pure and devoid of minerals that the mash would not reach the proper pH range without this Acid Rest. Most other brewing areas of the world did not have this problem.
Pale lager malt is rich in phytin, an organic phosphate containing calcium and magnesium. Phytase breaks down phytin into insoluble calcium and magnesium phosphates and phytic acid. The process lowers the pH by removing the ion buffers and producing this weak acid. The acid rest is not used nowadays because it can take several hours for this enzyme to lower the mash pH to the desired 5.0 - 5.5 range. Today, through knowledge of water chemistry and appropriate mineral additions, proper mash pH ranges can be achieved from the outset without needing an acid rest.
Doughing-In
To the best of my knowledge, the temperature rest (holding period) for phytase is no longer used by any commercial brewery. However, this regime (95-113°F) is sometimes used by brewers for "Doughing In"- mixing the grist with the water to allow time for the malt starches to soak up water and time for the enzymes to be distributed. The debranching enzymes, e.g. limit dextrinase, are most active in this regime and break up a small percentage of dextrins at this early stage of the mash. The vast majority of debranching occurs during malting as a part of the modification process. Only a small percentage of the debranching enzymes survive the drying and kilning processes after malting, so not much more debranching can be expected. With all of that being said, the use of a 20 minute rest at temperatures near 104°F (40°C) has been shown to be beneficial to improving the yield from all enzymatic malts. This step is considered optional but can improve the total yield by a couple of points.
The Protein Rest and Modification
Modification is the term that describes the degree of breakdown during malting of the protein-starch matrix (endosperm) that comprises the bulk of the seed. Moderately-modified malts benefit from a protein rest to break down any remnant large proteins into smaller proteins and amino acids as well as to further release the starches from the endosperm. Fully-modified malts have already made use of these enzymes and do not benefit from more time spent in the protein rest regime. In fact, using a protein rest on fully modified malts tends to remove most of the body of a beer, leaving it thin and watery. Most base malt in use in the world today is fully modified. Less modified malts are often available from German maltsters. Brewers have reported fuller, maltier flavors from malts that are less modified and make use of this rest.
Malted barley also contains a lot of amino acid chains which form the simple proteins needed by the germinating plant. In the wort, these proteins are instead utilized by the yeast for their growth and development. Most wort proteins, including some enzymes like the amylases, are not soluble until the mash reaches temperatures associated with the protein rest (113-131°F). The two main proteolytic enzymes responsible are peptidase and protease. Peptidase works to provide the wort with amino acid nutrients that will be used by the yeast. Protease works to break up the larger proteins which enhances the head retention of beer and reduces haze. In fully modified malts, these enzymes have done their work during the malting process.
The temperature and pH ranges for these two proteolytic enzymes overlap. The optimum pH range is 4.2 - 5.3 and both enzymes are active enough between 113 - 131°F that talking about an optimum range for each is not relevant. This optimum pH range is a bit low with respect to most mashes, but the typical mash pH of 5.3 is not out of the ballpark. There is no need to attempt to lower the mash pH to facilitate the use of these enzymes. The typical Protein Rest at 120 - 130°F is used to break up proteins which might otherwise cause chill haze and can improve the head retention. This rest should only be used when using moderately-modified malts, or when using fully modified malts with a large proportion (>25%) of unmalted grain, e.g. flaked barley, wheat, rye, or oatmeal. Using this rest in a mash consisting mainly of fully modified malts would break up the proteins responsible for body and head retention and result in a thin, watery beer. The standard time for a protein rest is 20 - 30 minutes.
The other enzymes in this temperature regime are the beta-glucanases/cytases - part of the cellulose enzyme family, and are used to break up the beta glucans in (un)malted wheat, rye, oatmeal and unmalted barley. These glucan hemi-celluloses (i.e. brambles) are responsible for the gumminess of dough and if not broken down will cause the mash to turn into a solid loaf ready for baking. Fortunately, the optimum temperature range for the beta glucanase enzyme is below that for the proteolytics. This allows the brewer to rest the mash at 98 -113°F for 20 minutes to break down the gums without affecting the proteins responsible for head retention and body. The use of this rest is only necessary for brewers incorporating a large amount (>25%) of unmalted or flaked wheat, rye or oatmeal in the mash. Sticky mashes and lauters from lesser amounts can usually be handled by increasing the temperature at lautering time (Mashout). See Chapter 17 - "Getting the Wort Out - Lautering" for further discussion.
The Starch Conversion/Saccharification Rest
Finally we come to the main event: making sugar from the starch reserves. In this regime the diastatic enzymes start acting on the starches, breaking them up into sugars (hence the term saccharification). The amylases are enzymes that work by hydrolyzing the straight chain bonds between the individual glucose molecules that make up the starch chain. A single straight chain starch is called an amylose. A branched starch chain (which can be considered as being built from amylose chains) is called an amylopectin. These starches are polar molecules and have different ends. (Think of a line of batteries.) An amylopectin differs from an amylose (besides being branched) by having a different type of molecular bond at the branch point, which is not affected by the diastatic enzymes. (Or, theoretically, feebly at best.)
Let's go back to our yardwork allegory. You have two tools to make sugars with: a pair of clippers (alpha amylase) and a hedge trimmer (beta amylase). While beta is pre-existing, alpha is created via protein modification in the aleurone layer during malting. In other words, the hedge trimmer is in the garage, but the clippers are out in the grass somewhere. Neither amylase will become soluble and useable until the mash reaches protein rest temperatures, and in the case of moderately-modified malts, alpha amylase may have a bit of genesis to complete.
Beta amylase works by hydrolyzing the straight chain bonds, but it can only work on "twig" ends of the chain, not the "root" end. It can only remove one (maltose) sugar unit at a time, so on amylose, it works sequentially. (A maltose unit is composed of two glucose units, by the way.) On an amylopectin, there are many ends available, and it can remove a lot of maltose very efficaciously (like a hedge trimmer). However, probably due to its size/structure, beta cannot get close to the branch joints. It will stop working about 3 glucoses away from a branch joint, leaving behind a "beta amylase limit dextrin."
Alpha amylase also works by hydrolyzing the straight chain bonds, but it can attack them randomly, much as you can with a pair of clippers. Alpha amylase is instrumental in breaking up large amylopectins into smaller amylopectins and amyloses, creating more ends for beta amylase to work on. Alpha is able to get within one glucose unit of a amylopectin branch and it leaves behind an "alpha amylase limit dextrin."
The temperature most often quoted for mashing is about 153°F. This is a compromise between the two temperatures that the two enzymes favor. Alpha works best at 154-162°F, while beta is denatured (the molecule falls apart) at that temperature, working best between 131-150°F.
Conversion Check
The brewer can use iodine (or iodophor) to check a sample of the wort to see whether the starches have been completely converted to sugars. As you may remember from high school chemistry, iodine causes starch to turn black. The mash enzymes should convert all of the starches, resulting in no color change when a couple drops of iodine are added to a sample of the wort. (The wort sample should not have any grain particles in it.) The iodine will only add a slight tan or reddish color as opposed to the flash of heavy black color if starch is present. Worts high in dextrins will yield a strong reddish color when iodine is added.
What do these two enzymes and temperatures mean to the brewer? The practical application of this knowledge allows the brewer to customize the wort in terms of its fermentability. A lower mash temperature, less than or equal to 150°F, yields a thinner bodied, drier beer. A higher mash temperature, greater than or equal to 156°F, yields a less fermentable, sweeter beer. This is where a brewer can really fine tune a wort to best produce a particular style of beer.
Manipulating the Starch Conversion Rest
There are two other factors besides temperature that affect the amylase enzyme activity. These are the grist/water ratio and pH. Beta amylase is favored by a low wort pH, about 5.0. Alpha is favored by a higher pH, about 5.7. However, a beta-optimum wort is not a very fermentable wort, leaving a lot of amylopectin starch unconverted; alpha amylase is needed to break up the larger chains so beta can work on them. Likewise, an alpha-optimum wort will not have a high percentage of maltose but instead will have a random distribution of sugars of varying complexity. Therefore, a compromise is made between the two enzyme optimums.
Brewing salts can be used to raise or lower the mash pH but these salts can only be used to a limited extent because they also affect the flavor. Water treatment is an involved topic and will be discussed in more detail in the next chapter. For the beginning masher, it is often better to let the pH do what it will and work the other variables around it, as long as your water is not extremely soft or hard. Malt selection can do as much or more to influence the pH as using salts in many situations. The pH of the mash or wort runnings can be checked with pH test papers sold at brewshops, and pool supply stores.
The grist/water ratio is another factor influencing the performance of the mash. A thinner mash of >2 quarts of water per pound of grain dilutes the relative concentration of the enzymes, slowing the conversion, but ultimately leads to a more fermentable mash because the enzymes are not inhibited by a high concentration of sugars. A stiff mash of <1.25 quarts of water per pound is better for protein breakdown, and results in a faster overall starch conversion, but the resultant sugars are less fermentable and will result in a sweeter, maltier beer. A thicker mash is more gentle to the enzymes because of the lower heat capacity of grain compared to water. A thick mash is better for multirest mashes because the enzymes are not denatured as quickly by a rise in temperature.
As always, time changes everything; it is the final factor in the mash. Starch conversion may be complete in only 30 minutes, so that during the remainder of a 60 minute mash, the brewer is working the mash conditions to produce the desired profile of wort sugars. Depending on the mash pH, water ratio and temperature, the time required to complete the mash can vary from under 30 minutes to over 90. At a higher temperature, a stiffer mash and a higher pH, the alpha amylase is favored and starch conversion will be complete in 30 minutes or less. Longer times at these conditions will allow the beta amylase time to breakdown more of the longer sugars into shorter ones, resulting in a more fermentable wort, but these alpha-favoring conditions are deactivating the beta; such a mash is self-limiting.
A compromise of all factors yields the standard mash conditions for most homebrewers: a mash ratio of about 1.5 quarts of water per pound grain, pH of 5.3, temperature of 150-155°F and a time of about one hour. These conditions yield a wort with a nice maltiness and good fermentability.
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