Enzymes and Diastatic Power



There are two processes in brewing history that were mysteries: the conversion of malt to sugars (saccharification) and fermentation. In 1857 Louis Pasture proved that yeast was responsible for fermentation and disproved the theory of “spontaneous generation of life”. Even further back in history, magic was given credit for the fermentation of beer and wine. Enzymes that convert starch to sugars were also not understood by the historic brewer. They just accepted that sweet liquid came from malt. As is turns out, the process is quite in depth and can be controlled to produce different beers from the same recipe.


The enzyme was first discovered in 1833. This discovery led to Louis Pasture’s discovery of yeast. Inside of yeast are enzymes called “invertase” that convert complex sugars (like sucrose) to simpler sugars (glucose and fructose). This process happens before yeast make alcohol and CO2 because brewer’s yeast does not turn sucrose directly into alcohol.


Enzymes are proteins that act as a catalyst to help complex reactions occur many times faster than they would have normally. A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Nearly all living cells need enzymes to perform chemical reactions at a rate sufficient for life.


Enzymes are selective for what substrate they convert among many possibilities. They are made up of thousands of amino acids which form a specific shape. This shape is meant to compliment other molecules’ specific shapes. If they do not match, then the enzyme will not react with that substrate. This basically means that enzymes are designed to perform a specific purpose on a specific molecule(s). These shapes are fragile and can be damaged or destroyed by either heat or agitation. If the shape is destroyed it will no longer match the other molecule(s) shape. This will reduce or destroy its ability to catalyze the desired reaction (denature). Denaturing is usually permanent. At the same time, heat can cause the enzyme to catalyze the substrate at a faster rate. Its peak activity is reached just before the temperature denatures the enzyme. At their high temperature range, the enzymes can denature in minutes (in a very thin mash).


The brewer can manipulate the wort’s fermentability by mashing at specific temperatures in the saccharification range (145-158 F) that emphasizes the action ofeither alpha or beta amylase enzymes. Lower temperatures enhance beta amylase and higher temperatures enhance alpha amylase. At the upper temperature limit of the beta amylase activity, alpha amylase becomes more active.


Alpha amylase breaks down starch molecules into non-fermentable long-chain dextrin sugar molecules in the range of 145-158 F. Beta amylase then goes to work on these long-chained dextrins and break them down further. Beta only works on the starches at the end of the starch chain one molecule at a time. Its temperature range is 131-149 F and primarily produces very fermentable maltose (the main sugar in wort).


In order to have very fermentable wort, but less extract, mash at 148 F. This mostly favors beta amylase activity. For a full bodied, less fermentable wort, but higher extract, mash at 158 F. Adjust the mash temperature to any degree in between to customize the wort. The extract changes with the temperature of the mash. At 148 F, the sugars are not as soluble as they are at 158 or even 170 (mashout temperature). pH is also a factor. 5.2 is the overall best pH for both beta and alpha amylase and slightly helps buffer the enzymes from denaturing.


Mash thickness is also a factor.

Experiment: Place 1 cup of malt in the microwave for 30 seconds. Remove the cup of malt from the microwave and take the temperature of the malt – it should be around 140 F. Put your finger in the malt. It feels warm but it’s not burning your finger. Now think of water at that same 140 F temperature. If you put your finger in water at that temperature, it would certainly burn your skin in seconds.


The same thing happens to enzymes in the mash. The greater the quantity of hot water to malt, the more the enzymes will denature. Because beta amylase is more sensitive to heat, a thick mash (1 quart water per pound malt) is favorable and will not denature as quickly, which enhances fermentability. Enzymes are most stable when bound to their substrate (starch). More water = less contact with the substrate.


A thick mash of 2 quarts water per pound malt will denature enzymes faster, but will increase the sugar extract from the wort. This is because the sugar flows better when it is less concentrated.


Putting all this together we see why mash schedules are done in a certain order. This is a general explanation of the process. The specifics are not given. The first water infusion brings the mash to a certain temperature and means that the mash is at its thickest, encouraging beta amylase. If a second infusion is done, it thins out the mash and increases the temperature which starts to denature beta amylase. At the same time, it increases the activity of alpha amylase. The final step is the 170 F mashout. Here the mash is at its thinnest, beta amylase is denatured, alpha is on its way out, and the sugars produced by the enzymes are made more soluble by the thin and hotter mash – ready for sparging. The only imperfect part of this process is increasing the temperature from beta to alpha amylase. In a perfect world, we could mash at a higher temperature and let alpha break down the long chain starch molecules and dextrins, then reduce the temperature and let beta nibble at the ends of those molecules creating extremely fermentable and high extract wort. Of course, it would make the beer very thin but high in alcohol. This is why mashes are done above 148 F to encourage both enzymes to work. Something else significant about 148 F is that this is the lowest temp at which barley is gelatinized (made soluble in water) and alpha amylase becomes sufficiently active. [The starch must gelatinize before the enzymes can get access to them.]

Helpful hints:

1) Introduce hot water to malt, not malt to hot water. By “doughing in”, the enzymes are better protected from the thin hot water.

2) For every degree the mash changes up or down, the final gravity will change by about .001 point or less.

3) Beta amylase optimum range: pH 5.5, 143F

4) Alpha amylase optimum range: pH 5.2, 152-154F


A test can be performed to see if the starch conversion is complete. Note that this test does not detect 100% of the malt starches. Perform an Iodine test. Iodine tincture must be used, not regular antiseptic iodine. This test will show a change in the iodine’s color in the presence of starch.


Iodine tincture starch test:Picture from: maltingandbrewing.com

  1. while mashing, take a tablespoon sample of the wort - no grain or husks
  2. let it cool to room temperature by spreading it out on a white plate or bowl.
  3. place a few drops of iodine tincture on the sample and next to the sample (so the color change can be seen)
  4. if the iodine on the sample remains the same, then the starches have been converted; if there is a darkening of the iodine, then there are still starches that need to be converted.
  5. Do not place the sample back in the mash!


The protein rest is another temperature range where different enzymes work. It takes place in between 112-140 F for 20-30 minutes in which certain enzymes break down proteins. This could reduce chill haze and improve head retention. With today’s fully modified malt, this rest is not needed. The proteins have mostly been broken down in the malting process. Some actually advise against this rest with fully modified malt because it can cause the beer to be thin. However, some homebrewers still practice it. One benefit of the protein rest is it can help break down the gumminess in unmalted or flaked wheat, rye, or oatmeal in the mash. However, making sure you mashout at 170 will also help reduce this gumminess.


Beta-Glucans are also worth mentioning. With under-modified malt, beta-glucans can be a problem. They are gummy and can slow or stop the sparge process. There is a beta-glucan rest that takes place at 98-113 F for 20 minutes. This breaks down the glucans without affecting the proteins. However, most all the beta-glucans in malt are degraded in highly modified malt, and this rest is no longer needed unless under-modified or high levels of unmalted barley are used.


The final mash rest I’d like to mention is the cereal mash. This does not involve enzymes. It is designed to make the starches in certain grains or adjuncts accessible to the enzymes in the saccharification rest. The cereal mash causes the starch to gelatinize – made soluble in water. For most grains and vegetables this happens between 120-140 F. Therefore, they can be mashed as normal provided there are enough enzymes to convert them (keep it under 25% when using 2 row). Other starches like rice and corn grits must be boiled to break down their starches.   This is done with a little malted barley, crushed and combined with the corn or rice and water and held at 158 F for 15 minutes, then boiled. Next it is cooled to mash temperatures and introduced in the mash.


In many specialty malts there are no enzymes and also no starches that need to be converted. The majority of crystal and roasted (black) malts have already gone through the saccharification rest during the malting process. They are moistened and brought to mash temperatures for the conversion to take place then roasted at high temperatures until done. These malts do not need to be in the mash. They can simply be steeped for 10 minutes or more at 150-170F to rinse the sugars from the grain. They can also be in the mash if that is your preference. Other malts have some enzymes, but not enough to “self-convert” its own starches. They need to be added to higher enzyme malt for full conversion in the mash.


Diastatic Power

Diastatic power refers to the amount of enzymes in the malt which will break down starches during the saccharification rest. The “diastase” enzyme group contains alpha and beta amylase enzymes which are responsible for converting these starches. The level of diastatic power is decided by the malting process.


Here’s a crash course in malting. Fresh grain is moistened and allowed to sprout inside the kernel. Once the acrospire (the leaf sprouting inside the grain) reaches about half the length of the kernel, it is dried to stop germination. This new growth dries up and falls off the grain and the kernel is now malted grain. This process breaks down most of the protein structure of the grain making it “fully-modified”. If this process is not completed or stopped early, then not all the proteins are broken down making it “under-modified”. A by-product of this process is the creation of diastatic enzymes.


Just like during mashing, these enzymes can be denatured by the kilning and roasting processes. Malts that are fully modified and lightly kilned have a lot of enzymes or diastatic power. In other words they have all the enzymes needed to convert their own starches to sugars in the mash. If the malt is kilned to a darker temperature, then some of the enzymes are denatured. When malt is roasted, all the enzymes are denatured. This is why black malt’s starches are already converted to sugars in the maltster’s process. If they weren’t, then there would be a lot of roasted starches in the grain and I don’t know that the enzymes would convert them – just my thought.


Diastatic power is stated in degrees lintner (°L not to be confused with degrees lovibond). A grain is considered to be self-converting if it has a number greater than 35°. The entire mash should average out to 70°L or more to efficiently convert the carbohydrates to sugars. Lower lintner malt will need to be combined with higher lintner malt to sufficiently convert its starches. The highest lintner grain is American 6 Row Pale. At 150°L it can easily convert itself and other under-modified malts. It has the most diastatic power because it is a smaller grain than 2-row. So pound-per-pound, there are more kernels in 6-row than 2-row. Perhaps the most common ̊̊̊̊̊malt used by U.S. homebrewers is American 2-Row Pale. It is about 140°L. British 2-Row Pale has a much lower diastatic power (40-71°L) because it is kilned to a higher color lovibond and some of the enzymes are denatured. It can only cover itself and a limited amount of under-modified malt. All crystal and roasted malts have no diastatic power, but their starches have already been converted to sugar during their cooking process. Malted wheat has a °L as high as American 2-row pale, but unmalted wheat has no diastatic power. Any grain that is unmalted will not have and diastatic power.


Maltsters list the diastatic power on their bags of malt. If you buy grain in bulk, then you’ll know your grains specific DP. This number is not consistent. There are variables that make the DP number change a little up or down.  Here is a basic DP chart.