Beer is driven by human imagination and produced by the chemistry of plant growth, post-harvest processing, brewing, and fermentation. At virtually every step, the transformations that produce beer and carry it to our lips involve manipulating temperatures to achieve specific outcomes.
The field of chemistry that deals with chemical reaction rates is called kinetics. The main principle of kinetics is that the higher the temperature, the faster chemical reactions occur. In a chemical reaction, the participants go from one stable state to another, overcoming a “wall” between the two by adding energy, which is often supplied by heat. There are countless ways that heat affects that chemical product we call beer, and many happen outside the brewhouse and are beyond the brewer’s control.
From the Roots...
It’s obvious that weather and climate affect crops in complex ways, from the aroma and bitterness of hops to the starch and protein content in barley. Once harvested, heat may be applied to a crop to reduce moisture—as with hops and kilning. In malt it’s taken further, becoming an active contributor to the creation of differently flavored malts, resulting in hundreds of flavor-active molecules that form beer’s unique malty backbone.
An important part of brewing is managing a system of plant enzymes to break apart starches into sugars. Temperature is one of the main levers of control. This control, for example, is what creates the difference between a highly fermentable, dry-tasting beer and one with a lot of unfermentable sugars and a rich, sweet personality, such as a doppelbock.
The chemistry becomes vastly more complex when we involve living creatures to ferment our beer. As their physiologies are exquisitely sensitive to temperature, this is another important control point.
As kinetics would suggest, yeast operate more enthusiastically at higher temperatures, but this is only partially a good thing for beer. The yeast have a lot to accomplish, and each of their many activities involves a multistep pathway and many intermediary chemicals. Some, such as esters, are pleasantly fruity and important in top-fermented beers. Others are not that pleasant or desirable, so it’s not usually a good idea to crank up the heat to get your beer in a hurry. In its preferred temperature range, each strain will take its time, releasing fewer of these bad-tasting by-products, and it will do a better job of cleaning them up after fermentation.
After all, that’s what beer conditioning is all about. Lager takes this to an extreme, with yeast at the very low end of their cold tolerance and a long, chilly conditioning. No wonder its flavors are clean and smooth.
Seasonal temperature management may well be what led to the development of lager. When Bavarians banned the brewing of full-strength beer outside the cold half of the year (as many countries did), they created conditions where a cold-tolerant hybrid yeast species could thrive. As a general rule, brewers there conditioned lagers in cellars over the summer to be enjoyed in the fall, while brewing weaker “small beers” for hydration through the warm season.
Okay, It’s Beer. Now What?
The unfortunate truth is that beer is an unstable product, never in a state of equilibrium. From the moment it’s packaged, it starts to change.
Even at room temperature, there’s plenty of heat energy available for chemical reactions, which is why beer stales four times faster when not refrigerated. It’s also acidic enough to encourage other reactions, such as the breakdown of fruity esters. Alcohol itself is plenty reactive, and certain oxygen-bearing molecules work their dark magic, creating stale, papery flavors.
The lesson here? Check those freshness dates. Most beers are good for a month then slowly decline, with both the lightest and most hop-forward beers aging most quickly. “Best by” dates for imports are often a joke. A golden lager is not “best” at a year old, or even six months.
Why Is Cold Beer So Appealing?
Refrigeration has become ubiquitous for most of us, but we retain cultural memory from the time when cold could only be provided by ice. In hot weather, this was a genuine luxury. Even today, it retains its soothing charm.
Before the era of refrigeration, people made every effort to keep beer as cool as reasonably possible. In Britain, this simply meant keeping the beer in the cellar and drawing it up to the bar with mechanical “hand pumps.” In the best circumstances, this kept the beer below about 60°F (16°C). In a moderate climate, this is plenty refreshing.
At these higher temperatures, though, beer can hold perhaps half to two-thirds of the carbonation typical of beers served “cold,” which is generally held to be 38°F (3°C) for lagers and similar light-bodied beers. British cask ales tend to be low in alcohol and relatively light in body. As carbonation can mask other flavors, cask ales show more malt and hop character—and they’re brewed for this as well. It’s a great example of how clever people adapt to technological limitations to create beers that work perfectly within those limits, sacrificing nothing. Their lack of gassiness and light body make them the perfect session beers, enjoyed in large servings.
Carbonation is simply carbon dioxide dissolved in a liquid, and colder temperatures allow more to be dissolved. There can be quite a lot—in beer, as much as two or three times the equivalent volume of the liquid at atmospheric pressure, sometimes more. When you pop the top off a bottle or can, the lowered pressure allows the gas to gradually leak out.
In very weak beer, the numbing chill in your mouth can be one of the strongest sensations, along with wetness—yes, there is a wet “taste”—and the tangy prickle of carbonation. The lightest beers (as with seltzers and sodas) lean on these attributes for much of their impact. When the chill goes away, so does the carbonation. At that point, this delicate flavor system pretty much collapses—so, to keep the flavor coming, drink quickly.
The Brazilians have a lot of warm weather and, not coincidentally, a lot of very dilute mass-market beer. One of their solutions is to serve their chope draft beer in little 10-ounce tapered pils glasses, and to serve it very, very cold. They give each beer a fillip of dense foam produced by a “creamer” faucet—a long-lived visual reminder of the carbonation that was present when the beer was poured. Japan has similar systems, serving light, dry (and cold) rice lager with a faucet to add some dense foam.
The Seasonally Shifting Joy of Beer
At one point, “drinkability” was simply an excuse for beer thinned out with adjuncts and extra water. You may not hear much talk about it, but this concept remains the cornerstone of all mass-market beer today. I’m not necessarily knocking it—some people just want to drink a lot of beer in a session, and that’s nigh impossible with IPAs and other big styles. Even with craft- and quality-minded enthusiasts, there’s a lot to be said for the easy drinkability of classic lagers. We see it in our pubs: People start with an IPA (or a double), then switch to something less chewy.
If you’re drinking to keep cool, it’s not a very effective strategy. Besides raising your body temperature, alcohol is also a diuretic, drying you out when you need to be hydrating. With less water in your system, you sweat less, so you’re less able to regulate your temperature. There are various strategies for managing this. Mexico and Central America have traditions of beers with additives such as tomato and lime juice—micheladas—often topped with salty-spicy seasonings (e.g., Tajin) that replace electrolytes and encourage sweating. And while this practice has little to do with flavor, adding ice cubes to an already light beer can refresh while mitigating dehydration. As my editor tells me, “Living in Bangkok, I never thought I’d enjoy drinking pale lagers like Singha poured over ice—but sitting outside on a hot night while eating some spicy street food, that is just the thing.”
As fall approaches, we enjoy a long tradition of darker, richer beers, such as the märzen and Vienna. The toasty Düsseldorfer altbier seems to have descended from erntebier, or “harvest beer.” It’s hard to scientifically explain, but these seem to go better with the cooler days and richer foods of the season.
There is still a tradition of “winter warmers” in Britain, although the term is forbidden on packaging in the United States—because it implies, er, um, something physiological? And we can’t have that. Still, strongish dark ales are generally the template for holiday ales, whether spiced or not. They do taste just right when there’s a nip in the air.
In the coldest months, there are warmed beers—or at least there used to be. In the days before central heating, the quickest way to warm up was to pour hot liquid directly down our gullets. Spiced beers, often spiked with spirits or fortified wines and enriched with eggs and cream, were the original “nogs” and can be quite tasty on a cold day. They’re fun and festive, with a lot of surrounding culture.
Give them a try this winter and give yourself a delicious opportunity to ponder how lucky we are to live on a rock in just the right temperature range to support life—and, thus, beer—and how even the slightest changes can lead to a completely different experience.