What makes malt go: diastatic power and proteolytic enzymes

barley malt

I made it through a whole hour-long presentation on malt without once mentioning diastatic power (what it is, how it works) or proteolytic enzymes.  Whups.  Thank goodness they were at least in my handout (see my last post for the handout).

a round plate divided into wedges, each full of a different kind of malt
Ah, the colors of malt!

So, to make up for this rather large omission, I’m going to discuss what they both mean to the homebrewer.  fair warning: I haven’t taken chemistry since tenth grade, we won’t discuss how long ago that is, just that I’m dealing with it in a very remedial, basic way.  If you’re happily technical this may drive you crazy.Remember the malting process: take grain, usually barley or wheat, and moisten it until it sprouts.  Stop the sprouting by drying the grain, and shake off the new rootlets and growth, then roast/toast the grain until it has the color/flavor you desire.

a small pile of wehat grains that have sprouted
Sprouted wheat

The enzymes formed in the process are catalysts – they cause other reactions without being changed themselves.  They are protein-based.  The malting process creates enzymes we homebrewers care about (which is why I should’ve included them, duh).  Malting is all about getting enzymes to break down starches into more accessible sugars and nutrients your yeast can access in the brewing process – without letting the sprouting seed greedily use it all up in its attempt to grow into a plant.The BJCP exam study guide gives a healthy dose of malt chemistry, but often forgets to tell us why the terms they use matter, or what it does for our beer.  So here’s a really basic view:  we brewers love the proteolytic enzymes, which break down proteins, and the diastatic enzymes which break down starches.  The starch chains native to the endosperm of a single grain of barley are insoluble.  We need them to float away in the water we administer, to become water-soluble.  Cytase enzymes  break down the cell walls so all of these sugars and proteins becomes more accessible.

Diagram of the parts of a grain: hull, endosperm, acrospire range, rootlets
A Wheat Germ, true of barley too

The Winning-Homebrew.com website says it very well (emphasis mine):Activating and deactivating enyzmes is what the mash is all about.

There are two groups of protein enzymes we focus on in brewing, peptidase and proteinase (protease).   Peptidase breaks down smaller amino acid chains released by proteinase, releasing nutrients used by the yeast.  Proteinase breaks down the very large protein molecules into smaller amino acid chains, which enhances the head retention of beer and reduces haze.  We call the process of activating the proteolytic enzymes the protein rest.

Ah, the mystery of the protein rest.  Remember for a moment that a “fully modified” malt is one where the sprouty bits have gotten 3/4 of the length of the grain to the whole length of the grain.  Less than that is “under modified”, more is “over modified”.  Getting a big batch of grain to all sprout about the same amount is a testimony to how carefully it’s all sorted by maltsters!

The protein rest isn’t what it used to be.  Now that most of us buy our malts mass-produced, they are almost all fully modified.  The malting allows the proteolytic enzymes to break down proteins so far that you mostly don’t need a protein rest these days.  if you do, however, know that most proteins in the wort aren’t actually soluble until the wort reaches the 113°-131° range. If you use a protein rest with fully modified malts, you will probably get a thin watery beer, since the proteins responsible for head retention and mouthfeel break down too far during the rest.  If you use an undermodified malt, or a large proportion of unmalted or flaked grains (like, more than a quarter of your grain bill), that’s when you need the protein rest.  The ideal protein rest temp is 122°F.

model of glucose molecule
Glucose molecule

I have made watery beer from not understanding the protein rest.The word for breaking down the enzymes too far for them to do their jobs is “denaturing“.  Temperature and pH can cause this, among other things.  To every enzyme its own preferred temperature range.

You hear brewers talk about diastatic power a lot.  Diastatic enzymes convert the starch resident in the endosperm of their grain into fermentable sugars and unfermentable dextrins.  The two that become active during the mash are alpha- and beta-amylase.  Now, I knew of amylase as the enzyme your mouth produces to break down starches in your mouth when you’re chewing food – it’s the first stage of human digestion.  So it’s weird to find it here but not so hard to remember.

cartoon of dog as carnival barker saying "see the amazing beer geeks"
See the Amazing Beer Geeks Geek Out

Fermentable sugars are glucose and maltose, which is essentially two glucose molecules bonded together. Dextrins are long chains of glucose molecules; they are byproducts of starch conversion, but they’re not fermentable and have no taste.  I wonder if this is like potato starch, because they do add body and mouthfeel.OK, to enhance alpha-amylase enzymes, your mash is best off at 158°F.  That’ll give you wort with a lot of dextrins (unfermentable sugars).  Your beer will have a thicker body and mouthfeel. I mash at 158°F a lot.

If it’s beta-amylase you want, it’ll break starches and dextrins into glucose, maltose, and maltotriose (three glucose molecules stuck together).  It’s fermentable sugar.  Best mash temps for beta-amylase are 140°-149°F.  You’ll get a drier, higher-alcohol beer. Go on, you big beer fiends.

For all you Libras out there:  Most of the enzymes work pretty well within an overlapping range of 145°-158°F.  If you want your beer thinner and more alcoholic, lean toward the low end; if you want more body, rest your mash toward the upper end.  A fair compromise temp is 152°F.

Now, there are also beta-glucanase enzymes.  Their job is to break down the (surprise!) beta-glucans present in the grain’s bran, as beta-glucans show up mostly as cellulose.  They can make the wort kinda gummy and un-clear if they’re not broken down, so hurrah for beta-glucanase.  If you’re using more than 25% unmalted grain – there’s that number again – you can use a rest that’s a lower temp than the usual protein rest ( 98°-113°F) for about 20 minutes, which should help break down the gums without affecting the proteins that give you your mouthfeel and head retention.  It is so weird to factor in gums – I keep thinking of Egyptian kings mummified in rare resins.





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