Make Me Sweat! Cool Tips for Hot-Weather Brewing

For centuries, brewing was a seasonal activity. Beer was brewed in the colder months and stored in caves. But the fermenters were empty throughout the summer because brewers could not control their fermentation temperatures. For many homebrewers, brewing is still a seasonal activity for the same reason. However, it doesn’t have to be. I live in Texas, but I brew year-round. As I’ll show you, there are many ways to ease or eliminate the problems of hot weather brewing.

Problems of Brewing in the Heat

There are two main problems with brewing in hot weather: maintaining cool fermentation temperatures and cooling the wort adequately after the boil. If the temperature in your brewing area is too warm—for example, if you don’t have air conditioning— you are limited to brewing only ales, or certain styles of ales. High temperature fermentations lead overly fruity smelling beers. These beers may also have high levels of fusel oils, alcohols with more carbon atoms than ethanol. There’s no escape from having to control the temperature of your wort; but these days there are many alternatives to help the summer brewer do just that. Of the two problems of hot-weather brewing, cooling the wort adequately is the easiest to remedy.

Warm-Weather Wort Cooling

For all-grain brewers, or extract brewers who boil their entire wort, wort cooling can be a problem in hot weather. The tap water used to cool the wort may be warmer than in the winter. It may not be warm enough to get the wort down to pitching temperature. Generally, you can only cool your wort down to about 10° F degrees above the temp of your tap water. If the wort is still too hot after cooling the yeast can be stunted or killed when it is pitched. For most ale yeasts, the wort should be, at a minimum, below 90°F. It’s much better if the wort is cooled all the way down to fermentation temperatures, however. Lowering the temperature to suitable fermentation temperatures becomes even more difficult if you pitch the yeast into a warm wort.

Homebrewers have a variety of methods to cool their worts. Some cool the wort by immersing their kettle in a large amount of water, for example in a large sink or their bathtub. Other brewers use a wort chiller, either a submersible chiller or counterflow chiller. In all cases, the temperature of the cooling water affects how quickly the wort can be chilled and the coolest temperature the wort can reach.

Homebrewers also have different target temperatures they wish to cool their worts down to. Some brewers want to cool their worts all the way down to fermentation temperatures and pitch the yeast at the temperature it will be fermenting at. See Table 1 for a list of common temperatures. Other brewers want to pitch their yeast when the wort is warmer. Their idea is to get the fermentation started quickly, then cool the wort down to fermentation temperatures.

If you cool your wort in the bathtub, adding ice to the tub will suffice to cool the wort if your tap water is less than 10° F lower than your target temperature. If you use a wort chiller, you will need to cool the stream of water entering the chiller. The easiest way to do this is with a “pre-chiller.” A pre-chiller is simply a submersible wort chiller that lies between you water source and regular wort chiller. The pre-chiller is placed in an ice-water bath to cool the water as it flows through.

If you use a submersible wort chiller, you can add ice to the pre-chiller reservoir after the wort has cooled for 5–10 minutes. In the initial stages of cooling, the difference in temperature between the wort and tap water will be great. Consequently, the initial cooling will be rapid. Adding ice early on does little except melt the ice. After 5–10 minutes, when the temperature difference between the wort and tap water has narrowed, add the ice to cool the wort down to your target temperature.

When using a submersible chiller, occasionally swirling the chiller around to create a slow whirlpool greatly increases the rate at which the wort is cooled. In a whirlpool, the hot wort flows by the copper tubing. Without a whirlpool, the area immediately around the copper coils cools quickly but the rest of wort cools more slowly. Be careful not to splash or agitate the wort when swirling the wort with the wort chiller. This can cause hot-side aeration. Hot-side aeration is any introduction of air into wort when it is above 86° F (30° C). Hot-side aeration causes beer to go stale more quickly than beers that have not been hot-side aerated. Swirl slowly and stop moving the wort chiller once the wort is moving. Wait for 5–10 minutes before repeating. You should also take care not to leave the cooling wort exposed to air when it can be helped; airborne bacteria and wild yeasts may contaminate it.

If you use a counter-flow chiller, you will need to keep the pre-chiller iced the entire time the wort is siphoning. You may also have to adjust the rate of siphoning if the wort is not being cooled enough. The slower you run the wort through the chiller, the more opportunity it has to cool down.

Cooling the wort quickly and efficiently takes a little more effort during hot weather. And, it requires ice and perhaps a pre-chiller to work efficiently. However, this is the easier and least expensive problem of the two hot-weather brewing problems to solve.

Control Fermentation

Keeping fermentation temperatures low throughout fermentation is tougher than just cooling your wort adequately. However, there are a variety of ways brewers can deal with this problem. The solutions range from costly to cheap, but the cheaper solutions require much more effort and attention on the part of the brewer.

As shown in Table 1, ales are usually fermented between 68°F and 72°F. Lagers require colder fermentation temperatures, usually between 45°F and 55°F. Above these temperatures, yeast will give off unwanted fermentation by-products such as esters and fusel oils.

Esters lend a fruity smell to beer. In moderation, these molecules are an important part of the profile of some beer styles. For example, we expect that an IPA should have a fruity ale nose to it. In excess, however, esters become overwhelming and undesirable. Beers fermented too warm can have a distinctive banana smell that most beer drinkers find objectionable.

Fusel oils are alcohol molecules with more carbon atoms than ethanol, the primary alcohol in beer, wine and spirits. At low levels, these accepted in certain styles of beer such as barley wines or other high-gravity brews. However, they are usually thought to be objectionable in most styles of beers. At excessive levels, they can cause health problems.

High-tech fermenters

Homebrewing is getting more high-tech as time goes on. If you are willing to spend some money on your fermentation equipment, starting at around $800 for a 7 gallon brewery, you can buy fermenters with built-in cooling equipment. With these fermenters you can completely control your fermentation temperatures throughout the summer.

A few different homebrew outlets [I’m referring to here, in case you want to mention them] sell small cylindro-conical (CC) fermenters (7 gallon and up) with built-in cooling options. These fermenters are smaller versions of the fermenters most brewpubs and microbreweries use. The are round (cylindrical) at the top and taper to a point (conical) at the bottom. Yeast and trub can be drawn off the bottom at any time, so you don’t need to rack to secondary. In addition, harvesting yeast is very easy.

These fermenters have cooling jackets, many filled with glycol, that circulate cold liquid through the walls of the fermenter. Self-cooled CC fermenters aren’t cheap, but you will be able to simply dial in the temperature you want to ferment at and forget about it. With a CC fermenter you can brew any style of beer in warm weather, including lagers. In some models you can even program the temperature to change over time. For example, you may want to perform a diacetyl rest at the end of your fermentation.

Full-Sized Brewing Fridge

Another way to keep your wort cool is to use a refrigerator. In a full-size fridge, you will have room for two 5–7 gallon carboys. Since they are taller and thinner, you will have room for 4–6 cornie kegs, which can also be used as fermenters.

In order to use a refrigerator to ferment beer, you will need an external thermostat to control the temperature inside the fridge. In most fridges, the warmest temperature setting, typically in the mid-forties, is too cold for beer. An external thermostat bypasses the refrigerator’s internal thermostat and allows the fridge to reach ale temperatures. All you do is plug the fridge into the thermostat, and the thermostat into the wall outlet. When the temperature inside the fridge is too high, the external thermostat turns on the power to the fridge and the compressor turns on. When the temperature inside the fridge has dropped below your set-point, the external thermostat cuts the power to the fridge. Thermostats such as this, made by Johnson Controls, are available at most homebrew shops; they cost between 50 and 100 bucks, depending on the model. You can tape the temperature probe to the side of the carboy so you are reading the temperature of the carboy instead of the ambient temperature inside the fridge.

The adhesive temperature strips, similar to those used in aquariums, can also tell you the temperature of your fermenting beer. Since fermentations generate their own heat, and it takes time for this heat to dissipate from the carboy, the temperature of your wort may not be the same as the temperature set on your temperature controller.

A brewing fridge allows you to brew any style of beer during warm-weather. Plus, once the beer is brewed, you can store bottles or kegs in the fridge. The only problem with brewing fridges is a small one. If the wort is warmer than the inside of the fridge, you can get suck back when using the U-shaped fermentation locks. Suck back is when the liquid in the fermentation lock gets sucked into the beer.

Suck back occurs because, as the air in the headspace above the wort cools, the air contracts. The contracting air pulls the liquid backwards through the lock. To prevent suck back, put the minimum amount of water in the lock to begin with. The lock will then “gurgle” backwards as well as forwards. Alternately, you may remove the fermentation lock when wort or beer is cooling. Cover the carboy opening with aluminum foil until the temperature has stabilized, then replace the fermentation lock. [This does happen before fermentation begins and possibly after it ends. An easy way to prevent it is to begin fermentation with a cotton plug “air-lock” or start fermentation warm and move it into the fridge after active fermentation begins. At UC Davis we would ferment warm and move the carboy to a cold room for aging. This also results in suck-back. To prevent we would take off the air-lock, use foil until the beer was cold and then replace the air-lock.]

Dorm-Sized Brewing Fridge

If you have an old dorm fridge from your college days, you can turn it into a fermentation fridge. As with a full-sized fridge, you will need an external thermostat. But, unlike full-sized fridges, you will need to build an extension to the fridge. Basically, you will place the carboy in front of the fridge, and the box will surround it. You can get as involved as you like in constructing the box. You can build a wooden frame and make the sides out of insulation. Alternately, you can duct tape a thick cardboard box to the fridge and insulate it with old towels.

With a dorm fridge-box, you can easily maintain ale temperatures in hot-weather. However, trying to brew lagers may put too much stress on your condenser.

T-shirt method

If you don’t have the room or the budget for a brewing fridge, there is a low-tech way of cooling your fermenter. If you place a wet T-shirt over the fermenter, it will cool down the wort inside the fermenter. The wet T-shirt method works because as water evaporates from the T-shirt, heat goes with it. To keep the T-shirt wet, set a pan of water next to the fermenter and dip part of the shirt in the water. As water evaporates from the shirt, water from the glass will wick up to replace it. You can also circulate water over the shirt with a garden-type pump.

You can increase the cooling power of the T-shirt method by pointing a fan at the fermenter. The air flowing past the fermenter displaces the air next to the fermenter. This air, laden with water vapor from evaporation, is replaced by drier air. This allows further water to evaporate from the T-shirt. And, of course, you can always add ice to the water pan. [This works even better if you put a garden-type pump in a bucket and pump water over the tee-shirt. The excess water flows back in the bucket and is recirculated by the pump.]

Another way to further the cooling power of the T-shirt method is to decrease the surface-to-volume ratio of your fermenter. Basically, if you split the wort in your 5–7 gallon carboy into two smaller carboys, you’ve increased the amount of surface area per unit of wort volume.

The T-shirt method is cheap, but only moderately effective. You can decrease the temperature of your wort by 5–15° F, depending on a number of factors. These factors include temperature of the water in the pan, relative humidity, and surface-to-volume ratio of the fermenters.

You can help yourself out by cooling your wort all the way down to fermentation temperatures and placing the fermenter in the coolest part of your house or apartment. In addition, you can “strike while the iron is cold”—watch the weather reports for cooler periods and brew the day before the cold front arrives.

You should monitor the temperature of your wort as the fermentation progresses. You can easily do this with a temperature strip. These sell for 2–3 bucks at homebrew shops and stick to the outside of your fermenter. By keeping an eye on the temperature, you’ll know when you need to add a fan or ice to your set-up.

Brewing at High-Temperatures

Sometimes, you just can’t avoid the heat. When I was a graduate student, I lived in an apartment without air-conditioning. And, I didn’t have the money to buy a brewing fridge. So, I was often brewing when the temperature in my room was up to 80° F. (Above 80°F, I figured it would be too risky to brew; I didn’t want to be drinking too many fusel oils.)

If you are stuck brewing at the upper end of the ale range, or even slightly beyond, there are a few things you can do to compensate for the higher temperatures. In addition, you can choose appropriate styles to brew, so that the effects of high temperature brewing are less at odds with the style parameters.

At higher temperatures, yeasts produce more esters; but there are other variables that influence ester levels. These variables include the yeast strain, amount of yeast pitched, wort gravity, and level of aeration. By controlling these variables you can partially counteract the effect of high fermentation temperature. Using these following techniques, you can brew ales at temperatures in the upper 70s.

Some yeast strains produce fewer esters. These are usually described as “clean.” Yeasts that produce many esters are labeled as fruity. If you are brewing at high temperatures, pick a clean yeast strain. See Box 3 for some yeast strains that can be used for warm-weather fermentations. The higher temperatures may cause your clean yeast to make fruitier beer than it would at the correct temperature. But, unless the fermentation temperature is excessive, you can brew a decent beer even with the extra esters.

You should likewise pitch a lot of yeast, up to one and a half times the recommended amount. For a 5 gallon batch, make a 3L starter in a large soda bottle. Pitch only the sediment. Essentially, you grow up the starter and throw away any esters produced in the yeast’s growth phase. Remember also that you can keep your starter cool by using the T-shirt method.

Thoroughly aerating your wort also lowers the amount of esters produced. Since more air dissolves in cold water than warm water, this is another reason to cool your wort all the way down to pitching temperature.

Finally, you can minimize ester levels by only brewing low-medium gravity beers in hot weather. Brewing at lower gravities also limits the amount of heat your wort generates.

With clean yeast from a big starter pitched into a well-aerated wort, you can brew a reasonably clean ale at 75°F. At temperatures between 75 and 80F, you may end up with a moderately fruity beer even with the adjustments I’ve mentioned. How fruity the beer is will depend on the yeast strain; some strains can still produce a clean ale at these temperatures. Above 80° F, beer brewed with a normal ale yeast would probably be undrinkable (and maybe even unhealthy due to elevated levels of fusel oils.) However, it is still possible to brew a Belgian ale or wheat beet at these temperatures.

If you choose to brew an appropriate style of beer, one where some fruitiness is expected, the esters will be less detrimental to your beer. British ales are good candidates for warm-weather brewing, bitters, milds, and porters are expected to have a bit of fruity ester smell. Stout is also a good choice as the smell of the roasted grain can partially cover up some of the fruitiness. See Box 2 for a beer that can be brewed at temperatures up to 80°F.

One final caution when brewing at high temperatures. The wort can pick up off-flavors from the trub fairly quickly. It’s best to rack the beer to secondary after 3–4 days. At high temperatures with lots of yeast, your primary fermentation will probably only take 2 days.


Hot-as-Hell British Bitter
5 gallons

OG 1.043
FG: 1.011
IBUs 40


  • 7.0 lbs of pale ale malt, or
  • 5.5 lbs of liquid malt extract (pale or light, unhopped), or
  • 4.5 lbs of dry malt extract (pale or light, unhopped)
  • 3/4 lb crystal malt (30°L – 40°L)
  • 12 AAU East Kent Goldings hops (bittering)
  • 1/2 oz Fuggles hops (dry hop)
  • Wyeast 1272 (if your fermentation temperature will be up to 75°F)
  • White Labs WLP001 (if your fermentation temperature will be up to 80° F)
  • Wyeast 1056 (if your fermentation temperature will be up to 80°F)
  • White Labs WLP008 (if your fermentation temperature will be up to 85° F)


Make 2.5 liters of yeast starter wort with 300 mL of dry malt extract. Refrigerate the starter overnight and shake it well to aerate. Pitch the yeast starter three days before brewing. For all-grain brewers, mash all the grains at 152°F for 1 hour. For extract brewers, heat the brewing water to 152°F and steep the crystal malt for 1/2 hour prior to boiling the water and adding the malt extract. Boil the wort for one hour, adding the Goldings to the wort once it begins to boil. Cool the wort down to between 65°F and 68° F. Aerate the wort well. Pour off the liquid from the yeast starter and pitch the yeast sediment. Let ferment 4 days. Rack to secondary and add dry hops. Bottle after another 4–7 days in secondary with 2/3 cup of corn sugar. Enjoy.


Fermentation Temperatures
80+ not recommended for most yeast strains
75-80 even with compensating techniques, ales will be fruity with most yeast strains
72-75 reasonably clean ales can be brewed with compensating techniques or appropriate yeast strain
68-72 normal ale fermentation temperature range
60-68 some ales are fermented at these temps (Scottish Ales, for ex.)
55-60 some high-temperature lagers brewed here
45-55 normal lager temperature range


Seventy-two degrees Fahrenheit is the commonly-cited upper temperature limit for most ale yeasts. However, some ale yeast strains perform well at temperatures above this limit.

In general, Belgian yeasts and wheat-beer yeasts are good high-temperature fermenters. A bit of esters are expected in these beer styles. In addition, according to Dave Logsdon, from Wyeast, “When temperatures increase above 78 F, a significant increase in fusel alcohols is likely for most yeast. Belgian yeast, wheat beer yeast, and wine yeast appear to have lower levels of fusels when fermented at the higher temperature range.”

Some “normal” ale yeast strains also work well above 72°F. Chris White, from White Labs yeast says, “California, WLP001, is the best high temperature yeast we have. Neutral character can be obtained even up to 80F. WLP008 (East Coast Ale Yeast) is used by one brewery in Taiwan that consistently ferments at 90F, and they report good beer flavor.”

Here are some strains that Mr. Logsdon and Mr. White recommend:

“Normal” ale yeast strains

White Labs WLP001 California Ale Yeast
White Labs WLP008 East Coast Ale Yeast
Wyeast 1099 Whitbread Ale Yeast
Wyeast 1332 Northwest Ale Yeast
Wyeast 1335 British Ale Yeast II

Belgian yeasts

White Labs WLP500 Trappist Ale Yeast
White Labs WLP550 Belgian Ale Yeast
White Labs WLP565 Belgian Saison Yeast
Wyeast 1214 Belgian Ale Yeast
Wyeast 1388 Belgian Strong Ale Yeast
Wyeast 1762 Belgian Abbey Yeast II
Wyeast 3787 Trappist High Gravity Ale Yeast

Wheat-beer yeasts

White Labs WLP300 Hefeweizen Yeast
White Labs WLP380 Hefeweizen IV Yeast
Wyeast 3068 Weihenstephan Weizen Yeast
Wyeast 3333 German Wheat Yeast
Wyeast 3638 Bavarian Wheat Yeast

Issue: Summer 2001