Hot Process: Exploring the Role of Heat in Brewing

March 1, 2017 By aab

As you feel the comforting cool sensation of that beer in your hand, consider that our universe encompasses an almost incomprehensible range of temperatures, from atom-slowing cold to raging infernos not even Dante could have imagined. We are fortunate to live in the zone where liquid water is possible, making life—and beer—possible.

Heat is a form of energy, and when applied it induces vibration in atoms and molecules. Ice, water and steam are chemically identical, differing only by the action of heat upon them. One principle in physics and chemistry is that the more heat you apply, the faster things happen. It’s fundamental to everything we experience around us, and that includes beer and the way it’s brewed.

A brewer’s job is to hijack a bunch of biochemical processes intended for other purposes, so paying attention to temperature is crucial. Each of the thousands of chemical reactions in brewing has an optimum temperature, so manipulating heat is one of the main tools brewers use to control their process.

Let’s start with agriculture. It’s well-known that temperature does a lot to determine the suitability of a particular plant to any region, and this is certainly true of grain cultivation. The traditional grains used for beer—barley and wheat—prefer temperate climates, and within that parameter, different breeds are suited to specific zones. Germany and the rest of central Europe, for example, can produce barleys with low protein and a very clean flavor, making them well-suited to the production of all-malt beers for which this area is famous.

Move to a warmer climate, however, and you get barleys with very different characteristics. Growing conditions in China and India generally create barleys with a greater proportion of husk, bringing more tannic, astringent material to the beer; this is a flavor you can definitely taste in beers brewed from local malt in those regions. The same is also true in Northern and Southern Africa, Central and South America and to some extent, the United States. Paradoxically, barley grown in cold regions can show the same husky characteristics, as the plant creates additional protective material to shield itself from threatening conditions.

Many of these extreme-climate barleys are also high in protein, which contributes haze in the finished beer. High protein also translates to copious starch-converting enzymes, allowing the use of adjuncts such as corn and rice to both dilute huskiness and make a beautifully clear beer. This is why American-style adjunct lagers developed as they did in the late 19th century and still dominate the world to this day.

Loaves of Beer

If you’ve ever had barley soup, you know this cereal has very little flavor in its unprocessed state. And I think if that flavor were all that barley could bring to beer, we might have given up on it long ago. Fortunately, a heat-related process transforms raw grain, developing nearly every malty flavor we recognize in beer, from bread to cracker to cookie, caramel and toffee, all the way through toasty into the roasted, chocolaty, espresso zone. It is not by chance that we use these descriptors, as the browning process known as the Maillard reaction is responsible for all these foody flavors and more. Ancient brewers in the Middle East knew this, using specialized malt kilns for grain and also for baking loaves of malted barley for use in brewing.

Heat is one of the most important variables in malt kilning, but time, pH, moisture and grain composition also play roles. No matter the color, most malt is heated for many hours at relatively low temperatures to drive off moisture. Yet even the palest malts develop some Maillard flavors. The chemistry is hideously complex, and I won’t bore you with it here. Brewers, however, are advised to understand it thoroughly as a cornerstone of beer flavor. Once dried, malts may be left in the kiln longer, sometimes at somewhat elevated temperatures, for additional flavor and color. Some specialty malts are transferred to drum roasters, similar to those used for coffee, to develop truly roasted flavors and deep, nearly black color.

Malts known as caramel or crystal are wet-stewed at mashing temperatures to convert the malt’s starches into sugars before they are roasted. This encourages a chemical reaction known as caramelization, resulting in honey, caramel, raisin, toffee and burnt sugar flavors. Look for caramel malt flavors in classic old-school American pale and red ales, where toasted raisin and burnt marshmallow notes are probably the most prominent flavor elements.

Hot Tub! Into the Brew

Heat isn’t just good for malt flavor development, of course. It’s the engine that drives the enzymatic processes that make beer possible. Each barley kernel is a seed. It comes into the world with the energy and tools it needs to sprout. Taking control of these resources is a large part of what happens during malting; the brewer simply continues the process in the brew house. This happens in a tub of hot malt porridge known as a mash.

Enzymes are key. These specialized proteins are everywhere in life, assisting chemical reactions and allowing them to happen efficiently at temperatures and energy levels far below the levels that would be required by brute force alone. Without them, life is just about impossible. Each enzyme has a specialized purpose and a set of optimum conditions, one of which is always temperature. In the brew house, much of enzyme activity involves the breaking apart of starches and other molecules.

Malt has a fair amount of protein, not all of which is in a form desirable in the finished beer. It’s a pretty complicated story, but protein in the right form is responsible for beer’s lovely and persistent head, plus much of its body. It’s sort of a Goldilocks situation, with too-large and too-small proteins being either harmful or not all that helpful, and the mid-sized ones being just right for beer’s head. Depending on the specific malt and the beer being brewed, the brewer may choose to use a temperature rest that allows proteinase (enzymes are generally named for the molecules they act on followed by the “ase” suffix) to act, typically around 122 degrees F (50 degrees C).

Starch is simply individual sugar molecules strung together into chains or bushlike structures. In brewing, the money is in breaking malt’s starch into fermentable sugars that the yeast can ferment into alcohol. This happens at somewhat higher temperatures than the protein rest: in the range of 145–165 degrees F (63–74 degrees C). We are fortunate in brewing to have two enzymes available for this purpose, each with a different action and slightly different optimum temperatures.

For most beers, we don’t necessarily need to squeeze every last drop of alcohol from the available starches. Some styles depend on unfermentables to add a rich sweetness—think Scotch ale or doppelbock, for example. Luckily, our two different starch-breaking enzymes make this possible. One operates by popping off two-sugar units called maltose from one end of the starch chains. Since these are highly fermentable, favoring this enzyme in the mash makes for a drier, more attenuated beer. The other enzyme attacks the large starch molecules more randomly, making smaller pieces that may or may not be fermentable, which results in a beer with less residual unfermentables.

After about an hour or so of this, the brewer has extracted the right amount of the right mix of sugars, and it’s time to ramp up the heat and stop the action of the enzymes, a step called the mash-out. After that, the mash is drained, usually with the addition of more hot water to rinse any remaining sugars from the spent grain. The sugary liquid, or “wort,” heads into the kettle and begins heating its way to a boil.

In its essence, this seems like the simplest part of the process: just a big pot of sugary liquid, heating until it boils. In many cases it is as simple as that. But there’s a lot going on. The wort is sanitized by heat, and hop bittering compounds are chemically transformed and incorporated, while unwanted volatiles are driven off with the steam. The process takes about an hour.

Because we are talking about a solution with proteins in it, after a few minutes we will begin to get some coagulation like you see in egg drop soup. Since the wort is rich in sugars and we are applying heat, we’ll see the same kind of Maillard browning that occurs in malt kilning. This is not necessarily a good thing.

In a dark beer, Maillard formation in the kettle may be pleasant, and even encouraged in some dark styles, but the science around beer staling is coming to a different point of view, especially in pale beer. While Maillard compounds can be quite tasty, they can also act in the oxidation process, first absorbing oxidative potential and then releasing it later when it’s unwanted. Some manufacturers are deconstructing the boiling process and re-engineering it in a way that’s more complex and expensive in terms of equipment, but which is much more energy-efficient and produces much cleaner-tasting beer with a longer shelf life as well. Also impacting the shelf life of beer is the amount of oxygen picked up through processes like stirring or splashing during brewing, a phenomenon known as hot wort aeration. Brewers and equipment manufacturers do as much as they can to minimize this.

Now we cool things way down, hopefully as rapidly as possible. Heat exchangers, using cold water flowing in an opposite direction from the hot wort, do the job pretty efficiently as the beer gets transferred to the fermenter.

Yeast will now turn the wort into beer. Being a living organism, yeast is exquisitely fine-tuned to its environment, including temperature. However, we’re purposefully not going to give it what it wants. Yeast actually is happier at much higher temperatures than are normally used for brewing. If we were to allow it to sizzle along at its preferred 100 degrees F (38 degrees C) temperature, the resulting beer would be a nasty soup of esters and smell a lot like nail polish. Of the many fermentation conditions a brewer can control, temperature is by far the most important. Sometimes an adjustment of a degree or two can noticeably change the aromatic profile, especially with complex phenolic yeasts used in Belgian ales and Bavarian hefeweizens.

Each yeast strain has a temperature range within which it produces the best-tasting beer. At the high end, it makes a lot of aromatic chemicals. At the low end it tends to be more neutral, and below a certain temperature it simply goes dormant. Fermentation is an exothermic reaction, meaning it creates more heat than it consumes, so if the tank is not aggressively cooled, the yeast will generate runaway thermal conditions—just ask any brewer that has ever had a refrigeration failure on a tank.

Typical ale fermentation temperatures are in the mid-60s Fahrenheit (17–18 degrees Celsius), although some Belgians can go a bit higher. Some saison yeasts can actually produce tasty beer in the 90-plus F range (32 degrees C), but they are an exception. Lager beer is an extreme in the opposite direction, employing a special strain tolerant of cool fermentation with a long, cold conditioning called “lagering.” Precipitated by the cold, haze-forming proteins settle out and the beer becomes crystal clear. Because fermentation is cool, the yeast produces very little flavor of its own. That means that the focus of a lager beer will be more on the flavors of the ingredients with few aromatic embellishments of fruit or spice from the yeast.

Beating the Heat

Beer is famous as the great summer refresher among beverages, but before refrigeration its manufacture was strictly limited along seasonal lines. Through much of Europe, brewing of full-strength or strong beers was limited to the winter brewing season, sometimes with the force of law, as with the famous decree of Bavaria’s Albert V that bookended the brewing season between the Feasts of St. Michael and St. George, Sept. 29 to April 23. Brewers knew the issues with high-temperature brewing: runaway fermentations leading to solventy levels of esters, plus a high probability of infection furthered by agricultural activity. So, as in the case of 19th-century Belgium, brewers restricted summer brewing to small or “single” beers even without government intervention.

Such prohibitions were never necessary in the U.S., as brewing was largely restricted to the northeastern quadrant of the country, where natural ice was cut from frozen lakes and rivers and stored for summer use. The availability of refrigeration coincided with expanding settlements in the West and Southwest from about 1880 onward. The lack of refrigeration in certain spots in the west—notably California—led to the creation of a historical oddity: steam beer. This was sort of an ersatz lager, fermented with lager yeast but at higher temperatures more typical of ales. San Francisco’s Anchor was the last survivor of this genre, but its beer was reformulated from the ground up in 1971. It’s clear from conversations with the legendary rescuer of the brewery, Fritz Maytag, that by that time, Anchor Steam was a shadow of whatever it had been in its heyday, so we may never know exactly what the real deal tasted like.

Not many beers benefit from aging beyond what the brewer has provided, but there are those rare, strong few that do need a dark, quiet corner to lie down in. Coolish temperatures are best—hence the term “cellaring”—but equally important is a relatively constant temperature without short-term swings that can hasten the breakdown of the beer’s protein structure and ruin its body and head.

Drinking Temperature

Beer tastes better when it’s properly served, and temperature plays a big role in that as well. Carbonation follows strict rules about temperature and pressure, so getting just the right amount of sparkle and foam in your glass takes the combined efforts of brewer and publican, along with a healthy dose of physics.

Serving temperature matters a lot. Each of those thousand or two aromatic chemicals that give beer its character has a point at which it vaporizes, and as a beer warms it releases more and more of them. While keeping each beer in its “Goldilocks” temperature zone is easier said than done, it’s worth the effort. No beer should ever be served at freezing or below. Paler lighter beers should land in the glass about 38 degrees F (3 degrees C). British real ales do well at cellar temperatures, below 60 degrees F (16 degrees C), and bigger, darker beers shine in the same zone. If your big dark beer is served too cold, you can do it a favor simply by holding the glass tightly in your warm hand and swirling gently. You’ll be amazed how quickly it warms up and what a difference this makes as the aromas start flowing out of the glass.

If you live in a place where the weather changes through the year, you can enjoy the full range of beer experiences, each in its own perfect context: brooding imperial stouts as the snow falls, rich and mellow doppelbocks as the day gets longer, then bright and hopeful maibocks as the daffodils bloom. And when it finally arrives, the warmth of summer unleashes a torrent of lighter and more refreshing brews from pils to wit to Kölsch to weisse and on to hoppier pales and IPAs. As the days grow shorter in the fall, it’s amber Märzens and even a pumpkin beer if it suits your fancy. Then as the snow starts blowing in again, festive strong and spicy ales reign supreme.

So the next time you’re sweltering in the summer or freezing your ears off, have a deep and satisfying sip and think about what those temperatures have done in the service of beer.