Beat the Heat
This is the time of year many homebrewers in the Northern Hemisphere start thinking about the rising temperatures. Other than just worrying about staying cool and hydrated on brew day, the heat can pose some very specific challenges to making the best possible beer.
The solutions to those problems range from cheap and simple to expensive and complex. Once you know your options, you can pick the best approach to keep yourself and your friends in beer all summer long. The good news is that it’s not really as daunting as you might think.
Why Does the Heat Even Matter?
Heat is a funny thing with brewing. When we talk about altering temperatures in making beer, most of the time we’re heating things to well above (e.g. mashing and boiling) or cooling things to well below (e.g. lagering and serving) the ambient temperature. For those processes, we can add heat with burners and heating elements or chill with refrigeration, so it doesn’t really matter if the ambient temperature is 40 °F (4 °C) or 100 °F (38 °C). Though perhaps those who use coolers or uninsulated mash tuns would prefer a nice warm day where their mash temperatures won’t drop as quickly.
So when does hot weather come into play? For most brewers it’s all about fermentation. Yeast is extremely sensitive to temperature and many ale strains have a fairly narrow band near 68 °F (20 °C) where they produce the ideal character we’re looking for. It’s no accident that this temperature range coincides with the average daily temperatures in many of the European climates where the strains were originally selected. Before widespread refrigeration, brewers were at the mercy of the seasons and chose yeast that performed well at their ambient temperatures.
This observation provides the first possible solution to beating the heat: Choose a yeast strain that likes it hot. For example, while there is a fair amount of mystique around the saison strains, many brewers ferment up to and into the 90s °F (30s °C).
Of course, limiting yourself to one style — even one with so much breadth as saison — isn’t everyone’s cup of tea. If you were to take most ale strains and certainly all lager strains well above their ideal temperature ranges you can expect an increase in fusel alcohols, esters, and acetaldehyde. Those are associated with solventy, fruity, and apple-like characters, respectively. Go high enough and yeast will halt fermentation entirely, stalling out
your batch.
So let’s get back to those basics of getting your fermentation under control and within the ideal temperature range for the results you are looking for.
Temperature Basics
It helps to understand two critical characteristics of heat that are relevant to brewing. The first may be obvious but it’s worth stating that you can only cool wort as cool as the coolant you’re using. Stated another way, if you’re using 75 °F (24 °C) tap water to cool wort you can only cool the wort to 75 °F (24 °C). In practice, the drop in the last couple of degrees will take a very long time so it is more likely that your wort will only be cooled to around 77 °F (25 °C) when using 75 °F (24 °C) water.
The second critical characteristic is that the rate of temperature change is proportional to the difference in temperatures (the delta-T) between the thing being cooled and the coolant. In other words, if you are trying to cool 100 °F (38 °C) wort, it will cool much faster with 60 °F (16 °C) coolant than with 80 °F (27 °C) coolant. The large delta-T at the start of the cooling process results in fairly rapid decrease in wort temperature. As the relative temperatures of wort and coolant merge (or delta-T decreases), so does the rate of wort cooling. You have probably observed this during your brewing as the initial temperature drop during cooling is fast and gets slower and slower as your wort approaches your coolant temperature.
Brew day – Chilling Out
As mentioned earlier, most of the brew day process is agnostic to the ambient temperature. If anything, warmer weather will give you a jump on heating your strike water, help you maintain your mash temperatures, and get you to a boil a little faster as you’re not losing as much heat to the air.
Things get interesting, though, at the end of the boil. The step of chilling is basically an exercise in changing temperatures from a rolling boil down to pitching temperature. In this section I’m going to describe variations of this process but note that not all will get you entirely to your final pitching temperature. In those cases where you come up short (or high, as it were) you just need to start your fermentation temperature control from this higher starting point and then wait until the temperature falls into the desired range before pitching your yeast.
The simplest way to make the temperature transition from boiling to pitching is to do nothing other than wait. You can read about no-chill brewing in more depth in the September 2014 issue of BYO, but in summary you just need a way to keep spoilage organisms out of the beer and then you let the heat dissipate into the air. Some people use tightly sealed temperature- and food-safe plastic “cubes” for this but a brew kettle with some foil around the lid works quite well. In this process the ambient air temperature is what is relevant for our cooling calculations. But air doesn’t carry away heat nearly as quickly as many other coolants so you can expect to wait overnight or longer. And on hot days you may never get all the way down to your target unless you can put the wort in an air-conditioned space.
The next simplest way and what many homebrewers start with is to fill a tub with water and ice and carefully put the brew kettle in there to chill. This can be very dangerous, though, as you are moving a large volume of very hot liquid. This approach does work, though, and if you’re able to do it safely the only downside is that it takes a long time to fully chill. Please note that you should never transfer your boiling wort directly to a glass fermenter as they are likely to shatter from thermal shock
In an ideal world you want this transition to be quick if for no other reason than that the sooner you can pitch your yeast the less time your wort is vulnerable to spoilage organisms. There are other advantages for minimizing cooling time, as quicker chilling stops the isomerization of alpha acids (assuming you do not want increased bitterness from your late hop additions), encourages a strong cold-break, and minimizes the creation of dimethyl sulfide (DMS).
With partial-boil batches, where a smaller amount of wort is boiled and water is added to hit the right gravity and volume for fermentation, an easy solution is to chill the added water. Depending on your volumes and targets it may make sense to put the added water in the freezer and get it near frozen.
Many homebrewers eventually move up to full-volume boils and use immersion or counterflow chillers that use tap water as a heat sink. This approach usually works well as groundwater is generally cooler than your pitching temperature. The colder the groundwater the faster and more efficiently those chillers work. As the weather warms, tap water often warms as well. Initially this just slows the process and requires more time and volume to complete the process but if the water is warm enough it may prevent you from hitting your target.
If you still want to quickly chill wort all the way to pitching temperature you have a few options. The first option is to use a pre-chiller in association with an immersion or counterflow chiller. These basically look like an immersion chiller and are often made from a coil of copper. To use a pre-chiller, connect it to the hoses supplying your cooling water and submerge the chiller in a bucket of ice water. The cooling water becomes cooler than the source groundwater, increasing your delta-T and thereby speeding cooling. Continue to add ice to the bucket as needed. The tradeoff to this approach is that it uses less cooling water but may require a lot of ice.
There’s nothing that says you need to waste that water down the drain, though. A simple solution is to use a submersible pump to run water through your chiller and then return the outflow back to the bucket. Fill a bucket with ice-water, drop in the pump and outflow hose, and recirculate cold water. Or give the whole system a boost by refrigerating the cooling water first. It’s easy to top off with ice as needed and while this can be slower than using a pre-chiller it can save on ice in addition to the massive water savings.
So having walked through the options for chilling I’ll remind you of the key point I called out earlier. There’s nothing that says you have to keep chilling with your chosen method all the way down to your pitching temperature. So when the mercury rises, consider saving yourself a lot of time and effort and just cutting off the chilling at a higher temperature and moving into fermentation temperature control. Of course this requires scrupulous sanitation as your wort will be vulnerable to spoilage for longer. But if your process is clean, as it should be anyway, there’s no reason you need to rush those last 10–30 °F (6–17 °C) of cooling.
Control Fermentation Temperature
When it comes to controlling fermentation temperature in the heat, the simplest solution is one of the most expensive. Having a dedicated fermentation fridge paired with a thermostat is an expensive but ideal solution. It’s simple because during the hot weather the only thing that the fridge needs to do is turn on periodically to keep things cool. Just make sure you don’t accidentally leave the temperature probe outside the refrigerator like several brewers I know have done!
Not everyone has the money or space to commit to a fermentation fridge, though, and there are plenty of other options that can work well enough most of the year. Some struggle considerably when it gets hot so let’s talk about what works and what does not.
First off, to get the easiest solution out of the way, if you can move your batch into an air-conditioned space you can neatly avoid a lot of problems. No air conditioning or no fermentation space where there is A/C? Well, keep reading.
Many start in the hobby with either putting their fermenter in a cool interior closet or a tub of water with ice or frozen water bottles. Cool interior closets are harder to find in the summer but don’t forget that basements and root cellars often stay cool since ground temperatures are much more stable than air temperatures. The temperature also fluctuates less in basements. If you have a basement, put a thermometer down there and see if the temperature will work for fermentations.
As for the tub of water, you’re just going to need to babysit the fermentation more frequently. Remember how we talked about a large delta-T helping to cool things quickly? Well the reverse is true as well, and a large delta-T of the warm ambient air compared to your fermentation temperature will heat things up quickly as well. What used to be a frozen water bottle a day can quickly become four or five. So keep a close eye on things, and keep your freezer full of substitute ice bottles so they are on hand when needed.
Building a fermentation chamber out of insulating material or a large cooler can minimize heat gain and the amount of work you need to do to keep things at the right temperature. If you don’t have a cooler big enough, you can use rigid insulating foam sold at hardware stores to make something custom. If you take that approach, make sure to carefully tape all the seams and consider using canned spray foam to minimize air leaks. Weather strip around the lid as well and weigh it down to ensure there’s a tight seal. Just like a commercial cooler, if warm air can get into your chamber your efforts will be greatly diminished.
At various times over the years, I have heard the advice that you can use a wet t-shirt or towel on a fermenter in a pan of water with the idea being that evaporation will help cool your fermentation. I haven’t had much luck with this approach in extreme heat because the evaporative cooling effect is so small. The impact is also decreased dramatically as humidity rises. If you live in a region where swamp coolers are effective then this may be something to consider, though. But keep vigilant against the risk of mold and mildew growing on the shirt.
There is a cooling technology that is often more affordable and sometimes more space-efficient than refrigerators: The thermoelectric cooler (TEC). Rather than having the moving parts and refrigerant, a TEC works by running electric current through a special material to create a heat pump. One side of the TEC is hot and the other is cold. So for a cooling operation you typically will have the cool side in contact with the fermenter and the hot side will have metal fins to help dissipate heat to the air. You may have seen TECs in cheap soda can coolers and some wine fridges. They have the benefit of being cheap, durable, and quiet.
The problem is that TECs are generally limited to cooling an amount relative to the ambient temperature. They rely on a delta-T between the hot side of the device and the air. It’s not as simple as just running them more frequently or with more power to get to lower temperatures. If you already have one of these you will want to focus on helping out the TEC as much as possible. Ensure you have complete insulation and no air leaks in your fermentation chamber. Also, if the chamber is enclosed, consider putting ice in there like a cooler.
Ultimately I wouldn’t recommend TECs for dealing with fermentation in hot weather as they are better suited to times when you are trying to maintain your beer at temperatures closer to ambient. If you do want to further explore this option, make sure to carefully read the specifications sheet so you can be sure it will work in your situation. You’re looking for the number of degrees cooling below ambient and you need to take into account the temperature where you’ll be fermenting.
What Works Best for Me
One of the great things about this hobby is that every brewer gets to decide what they value and can then use that to guide their choices. For me, I value making great beer with minimal wasted time and effort, at the expense of a few key purchases. In other words, for the same reason I gave up on bottling and went to kegging, I didn’t have the patience to babysit buckets of ice or frozen water bottles.
For me, I like the water savings and time efficiency of a counterflow chiller. I upgraded to one with a convoluted copper core since it has a large surface area between the coolant and wort, introduces additional turbulence in the flows, and maintains easy cleaning and sanitation. When groundwater temperature climbs, I simply accept a higher cutoff point for my chilling step and stop after about 5–10 minutes. At the hottest times this still usually gets me down to the mid-90s °F (~35 °C). I pop my fermenter into the fridge and set my thermostat for my fermentation temperature. Typically, I leave that overnight and pitch the yeast first thing in the morning (about 10 hours after flame-off.) I’m very careful with sanitation so this hasn’t been an issue and I’ve followed this basic process for about a decade.
Conclusion
Remember that hot weather only impacts a small portion of the brewing process and there are clear solutions you can apply to keep things under control. The great news is that any investment you make to deal with the heat will likely pay off year-round with shorter chilling times, more consistent fermentation temperatures with less effort, and perhaps even the ability to brew lagers. So don’t let a heat wave put a halt to your brew schedule.
