Chapter 14 - How the Mash Makes Wort
The Acid Rest and Modification
The Protein Rest
The Starch Conversion/Saccharification Rest
Manipulating the Starch Conversion Rest
Mashing is the brewer's term for the hot water steeping process which 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. When mashing malted grain, the brewer is concerned with two main classes of enzymes: proteases (or proteolytic enzymes), and diastases (or diastatic enzymes). Proteolytic enzymes break down long complex chains of protein molecules into simpler and more useful proteins and amino acids. Diastatic enzymes convert starch molecules into fermentable sugars and unfermentable dextrins. Each of these enzymes is favored by different temperature and pH conditions. A homebrewer can adjust his or her mash temperature to favor each successive enzyme's function and thereby customize the wort to their taste.
The starches in the mash are about 90% soluble at 130 °F and reach maximum solublity at 149°F. Unmalted grains have their starch reserves locked in a protein matrix which prevents the enzymes from being able to physically contact the starches for conversion. Only by crushing or rolling the grains is the matrix broken up. The starches can be gelatinized (made soluble) by heat alone or by a combination of heat and enzyme action. Either way, a mash is needed to convert the soluble starches to fermentable sugars.
Figure 11 - Typical Enzyme Ranges in the Mash
Table 5 - Major Enzyme Groups and Functions
|Enzyme||Optimum Temp Range||Optimum pH Range||Function|
|Phytase||86 - 126°F||4.4 - 5.5||Lowers the Mash pH. No longer used.|
|Beta Glucanase||98 - 113°F||4.5 - 5.0||Best gum breaking rest.|
|Peptidase||115 - 135°F||4.6 - 5.2||Produces Free Amino Nitrogen (FAN).|
|Protease||115 - 135°F||4.6 - 5.2||Breaks up large proteins that form haze|
|Beta Amylase||130 - 150°F||5.0 - 5.6||Produces small, highly fermentable sugars.|
|Alpha Amylase||155 - 167°F||5.3 - 5.8||Produces larger, less fermentable sugars|
Doughing-In/ The Acid Rest
To the best of my knowledge, this temperature rest (holding period) is no longer used by any commercial brewery. It is sometimes used by homebrewers for "Doughing In"- mixing the grist in with the water to allow time for the mash to liquify and time for the enzymes to be distributed. The use of the a 20 minute rest at temperatures near 100°F (40°C) has been shown to be beneficial to improving the yield from all enzymatic malts. This step is considered to be optional but can improve the total yield by a couple of points.
Before the turn of the 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. This stage is known as the Acid Rest but it is not used nowadays. 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.
The Protein Rest and Modification
Modification is a term which describes the degree of breakdown during malting of the protein-starch matrix (endosperm) that comprises the bulk of the seed. Moderately-modified malts need a protein rest to utilize the proteolytic enzymes that are responsible for breaking down the large proteins into smaller proteins and amino acids as well as the beta-glucanases/cytases to release the starches from the endosperm. Fully-modified malts have 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 brewing, these proteins are instead utilized by the yeast for their growth and development. 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 enzymes overlap. The optimum pH range is 4.6 - 5.2 and both enzymes are active enough between 115 - 135°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 125 - 130°F is used to break up the proteins which might otherwise cause chill haze and can improve the head retention in beers made from lightly kilned and/or less-modified malts. The standard time for a protein rest is 20 - 30 minutes. If the rest is too long, the head retention and body of the beer will be diminished. This rest should only be used when using moderately-modified barley malts, or a large proportion (>25%) of flaked barley, wheat, rye, or oatmeal. Otherwise there is usually no need with today's fully-modified malts.
The other enzyme in this temperature regime is glucanase- part of the starch enzyme family, and is used to break up the beta glucans in (un)malted wheat, rye, oatmeal and unmalted barley. These glucan hemi-celluloses 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.
Starch Conversion / Saccharification Rest
In this stage the diastatic enzymes start acting on the starches, breaking them up into sugars (hence the term saccharification). One group, the amylases, are enzymes that work on the more complex starches and sugars. The two main amylases are Alpha and Beta. Alpha works by breaking up long, branched starch chains at the branch points, leaving behind a variety of straight chain starches and dextrin-type sugars. The reduction of these large branched chains reduces the viscosity and "liquifies" the mash. Beta amylase works by separating these straight chains into fermentable maltose sugar units.
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 158F, while beta is denatured (the molecule falls apart) at that temperature, working best at 140F. The mash liquification function of alpha amylase is effective at temperatures as low as 120°F.
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 150F, yields a thinner bodied, drier beer. A higher mash temperature, greater than or equal to 158F, 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.
Testing Your Conversion
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.
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 5.4. Alpha is favored by a higher pH, about 5.7. However, a Beta-optimum wort is not a very fermentable wort, Alpha amylase is needed to break up the larger chains so Beta can work on them. A good analogy is to visualize making firewood from a stand of oak trees. If you picture Alpha as being a chainsaw and Beta being a splitting maul, you can understand that you need both tools to make the firewood. The chainsaw can cut off the branches and cut the logs to lengths that the maul can split into useful pieces.
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 153-155F and a time of about one hour. These conditions
yield a wort with a nice maltiness and good fermentability.