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How to Keep Your Fermenter Cool

We all want to make good beer during the summer, but when temperatures are above 90 degrees outside, it's just too hot to ferment anything other than Belgian farmhouse ales. 

Ale-makers... don't despair!  Here are a few tips that actually WORK:

We all know most ale yeasts do their best work between 62º and 70ºF.  Rest assured, they'll ferment at 85º or 90º and be quite successful.  But they won't be very kind to your brew.  Acceptable temperature ranges can often be difficult to achieve during the summer months, unless you are willing to have your air conditioner blasting 24/7.   Since most of us can't afford an electric bill which yields 300 dollar batches of beer, it's nice to know there are easy and affordable means of keeping your fermenter cool during those hot summer months.  There's a simple method which works well in hot temps, even in the desert southwest. 

What do you need?  All you need is a common household wash tub, large enough to handle the size of your fermenter, and a little ice.  Your existing kitchen refrigerator/freezer should be able to produce enough ice for the job.   Wash tubs can be purchased at any household store where such items are found.  We also carry them here at the shop during the summer months.  They usually aren't more than $10.00 in price.  Plastic tubs are preferable, but any wash tub will work.

Here's what to do: 

While you are chilling your wort, fill your wash tub about 1/3 full with cold tap water, no higher up than the Fermometer will be once the fermenter is setting in the "bath".   You don't want your Fermometer in contact with water for an extended time.  Fill the water in the wash tub low enough to account for water displacement as the fermenter is set into the bath.  Remember, keep the Fermometer dry.  If it's too low, purchase another, and place it horizontally halfway between the bottom of the fermenter and the five gallon-mark.

Next, make sure your washtub water is chilled to the same temp.  If you want to pitch at 64º, get your water to 64º.  If your tap water is warm (usually the case in the summer) use some ice in the wash tub to help get the water down to temperature. 

Once you're chilled and ready to pitch, your wort is already at the correct temperature.   All you need to do, is keep it there!   The water bath is the way you do it.  Every day the temps of your house can rise and fall according to the daily temperature spikes.  Eventually an uncontrolled fermenter will creep up to the household temperature average, which is likely higher than the ideal temperature range of your fermentation. 

The secret to maintaining a constant temperature in the fermentor, is to allow the water bath to absorb those daily temperature spikes, rather than your fermenter.

The water acts as an insulator... like a refrigerator.  The water not only absorbs the daily temperatuire spikes before the heat can reach your fermenter, it also helps to draw out considerable heat created by the fermentation process.

We have found that most styles of ale yeast make great beer when fermenting around 68F.  Since the process of fermentation generates heat, the temperature of your beer can rise 4-6 degrees very quickly.  Therefore, it is recommended to chill the wort around 4-6 degrees cooler than the target temp.  The yeast manufacturers usually provide a target range for each strain.... follow their instructions.

Remember, it's about control.  If you allow the yeast to get too warm, they will produce esters and other compounds which will contribute flavors not necessarily desired in your beer.  Keeping the water around 64F will allow room for the spike in temperature created during the vigorous attenuative phase, which will keep flavor production under control.  During the vigorous stage (high krausen, rapid airlock activity) the water bath might be 64F, but inside your fermenter it will be warmer.  Knowing this, and preparing for it, will improve the quality of your beer ten-fold.

Every home is different.  Some are hotter than others.  You will need to get a feel for how quickly heat is absorbed into your water bath.  Some people will need to put a handful of ice into the water every morning to keep it at 64º.  Others might have to do this once in the morning and once in the evening.   Every house is different, so you may need to monitor your temps several times a day until you have a feel for your own household environment.

For example, we know some starving college students who live in a hot apartment near the brewshop.  Their a/c doesn't work well, and their freezer doesn't have an ice-maker.   Like all college students, their thirst for good beer kindled their ingenuity.  They came up with a simple yet affordable way to regulate their fermentation temperature.

They picked up a twelve-pack of bottled water for a few bucks at the supermarket, and placed the bottles in their little freezer.  Froze 'em solid.  Every morning before class, they'll put four of them into the water, spaced evenly around the fermenter.  When they get home in the evening, they'll swap them out with new frozen bottles, and rotate the old ones back into the freezer.  Their apartment is much hotter than most, but it is working well for them. 

Other people take it one step further.  They make 'swamp coolers' out of their wash tubs.  They take an old t-shirt and place it over the fermenter with the airlock sticking out the neck, and the bottom of the shirt soaking in the water.  After a few minutes, water will begin 'wicking' up the sides of the t-shirt, and as it climbs it evaporates, which cools down the surface of the fermenter.  Pretty handy!

Once you get the hang of it, you can make great beer during the summer no matter how hot it gets in your house.  If your house stays above 90... maybe you should address that issue first!  Or perhaps the Belgian styles are more appropriate.  

One last (but important) note... temperature control is only critical for the first 4-5 days, as this is when most flavor production occurs.  After that time, it is optimal to allow the wort temperature to rise... to around 72 degrees.  This helps delay yeast flocculation, which encourages the yeast 'finish' the beer. 

Cheers!