The other night, over a glass of porter, Erica asked me how to make a sweet beer. It was a reasonable question – the porter in question is big, boozy, and sweet in the same way that a bar of Sharffenberger 62% is big, chocolatey, and sweet.
“Put a lot of sugar in it,” I answered.
Now before you go and think that my wife and I frequently play the snappy-answers game, I did elaborate and, because the real answer gets at a lot of the craft of making a beer, I am at her request sharing that information. If you are a brewer, perhaps this will give you another arrow in your quiver of brewing skills. If you are not, I hope it is an interesting insight into the science (and black magic) of the brewmaster’s science (and art).
All beer starts with sugar water. Brewing writer Randy Mosher once likened wort, the first intermediate stage in a beer’s production, to sweet beef and barley soup, but without the beef. Wort is produced in a process called mashing, where malted barley soaks in hot water. Malted barley is, basically, barley that had begun to sprout before being kiln dried and having its lifecycle put on pause for a while.
Once re-wetted, that lifecycle kicks back into gear, but now at an accelerated pace, thanks to the high temperature of the water – usually anywhere from 148 to 158 degrees Fahrenheit. Actually, the barley never sprout, the drying took care of that, but a complex cocktail of enzymes will go back to work – turning the starchy grains into sweet sugars. Normally this process proceeds at a pace designed to mirror the needs of the sprouting grain, which depends on the released sugar to nourish initial growth.
But in hot water, everything goes faster and in just an hour or less the enzymatic magic is complete.
Now the main reason we want this sweet water is to nourish the yeast – the little microscopic beasties that do the dirty work of making the alcohol. Yeast eat the sugar, make the alcohol, yum.
If yeast are going to come along and eat the sugar, then how do we make a sweet beer? Why does’t more sugar just lead to more alcohol? There are a couple of approaches.
First off, brewer’s yeast will only survive up to a certain alcohol level. Eventually, the yeast will get sleepy and slow, just like humans do above a certain alcohol level. So a sufficiently “big” beer can have plenty of residual sugar. Just mash enough grains, produce enough sugar, and once your yeast have gotten drunk and died, there will be some unfermented sugar left over.
We are taking BIG beers here though, above seven or eight percent alcohol, higher for some yeast strains (Belgians). That’s at least 50% above the typical brew.
So without producing massive intoxication and venturing into malt liquor land, there is one other way to get a sweet beer.
Yeast, as it turns out, are simple creatures and can only ferment short chain sugars. They are incapable of fermenting longer, complex chains of sugar molecules, what brewers collectively refer to as dextrins.
If we can yield a wort with more of these dextrins, at the expense of shorter and more fermentable sugars, the result would be a beer with sugar leftover. And it turns out we can, by taking advantage of the complexity of the enzymatic cocktail in those malted barley grains. The two key enzymes are Alpha-Amylase and Beta-Amylase. The former produces short, fermentable sugar and the latter long, unfermentable sugar.
In a fairly complex way, lower temperatures favor the action of the Alpha-Amylase. It is the more aggressive enzyme and, at a mash temperature of around 148 Fahrenheit will do by far the majority of the work. The result? A clean, dry, crisp beer that is great for a summer day, shows off bitter hop aromas, and leaves the drinker feeling refreshed.
Raise the temperature and the Beta-Amylase grows more aggressive and Alpha-Amylase stats to actually get a little overcooked and to break down. Around 158 degrees you get a beer that is big, sweet, and going to nourish the drinker through a cold winter day.
Now these are extremes (particularly the high range), and most beers land somewhere in the middle. Other factors (pH, water/grain ratio) influence the production of dextrins vs. short sugars as well, but I personally tend to take the approach of holding everything else constant and just fiddling with one variable at a time – my mash temperature.
Brewing textbooks tend to have lots of charts and graphs showing how these different factors interact. The relationships are subtle and the effects disproportionately dramatic (a 5% change in dextrin content is the difference between summer-crisp and winter-nourisher). But in reality it is all black magic. Even the most teutonically scientific of brewers will admit that the interplay of variables means that it all boils down to experimentation, trial and error.
The porter mashes at a toasty 158. It is always a scary moment, because just a couple degrees higher and enzymatic action shuts down for good and the tender Amylase molecules (Alphas and Betas) denature and disintegrate into useless fragments. But the result, when I hit it, is a dark, full, sweet, sweet fall season brew.