TIPS AND TECHNIQUES: How to Control Fermentation Temperature Better?

Fermentation temperature control is the single most important thing you can do that will make the most dramatic improvements in your beer. And it can be a big problem, especially when brewing in the Deep South. Winter brewing is great but summer brewing can be brutal in the 100°+ days. Without temperature control, it’s simply impossible to brew most beers correctly. Many homebrewers underestimate its importance and therefore are doomed to brew mediocre beers.

Some of the major problems associated with fermenting too warm are as follows.

What Happens if Your Fermentation Temperature is Too Warm:

  • The biggest problem is the off flavors from esters and fusel alcohols that the yeast produce. Sometimes the flavors are not so much “off” as they are inappropriate for the style.
  • Your yeast can blast out of the starting gate, consuming everything in sight, then run out of nutrients before finishing the sugar. This usually ends in an incomplete fermentation.
  • Poor fermentation temperature control often results in fermentations that are too hot, causing the yeast to become too sensitive to alcohol toxicity (meaning that they will die off from the alcohol before their usual tolerance is met).
  • Yeast begin to die off from heat stress, leaving the remaining yeast to do all the work. In effect you ended up under-pitching the yeast and will get off flavors as a result.
  • Since yeast metabolism generates a lot of heat, starting fermentation at too high of a temperature will quickly lead to problems as the temperature will climb in the 80°F+ range and yeast die off.

What Happens if Your Fermentation Temperature is Too Cold:

When brewing in colder climates or during the winter without temperature control, yeast will exhibit stress problems too. Winter is the traditional time to brew because there is less spoilage bacteria and wild yeast to contend with. For a homebrewer, too cold of a fermentation temperature can cause the following problems:

  • Your fermentation may never get started.
  • Your fermentation may be sluggish and drag on for weeks before finally getting stuck.
  • For ales that require a degree of fruitiness from esters, fermenting too cold can lead to a beer that is too clean or bland for the style. Judges will be looking for flavors and aromas that just didn’t make it into the beer due to the cold fermentation.
  • If there is any contamination in your beer, it is going to be a race to see which can dominate the fermentation. A sluggish start from poor temperature control can give these bacteria a chance to take over and ruin a batch of beer.
  • When fermentation does commence in an environment that is too cold, CO2 becomes entrained in the cold beer. Flavors that are normally “gassed off” stay in solution and may make it through the entire fermentation process to the final product. This is especially true for the “sulphur” aromas and flavors produced in lager fermentations.

Monitoring Fermentation Temperature Control

So what are the solutions?

What can you do to control your fermentation temperature? It goes without saying that before you can use temperature control in your fermentation, you must know what that temperature is. There are a few options for temperature measurement are:

  • A separate thermowell with temperature probe installed will give you the exact temperature of your fermentation. This is the most accurate way to measure and control the temperature of the fermenting wort.
  • Or you could rely on the setting on the dial of your temperature controller. You want to control the actual temperature of the wort and not the ambient temperature inside the fridge (which can vary by quite a bit). To do this, tape the temperature probe to the side of your fermenter and then tape a piece of bubble-wrap on top of the probe for insulation.
  • For measurement only, an indoor/outdoor thermometer works well for monitoring the ambient temperature inside your refrigerator. Place the control unit on the outside of your fridge, and the temperature for the outside (which is now inside your fridge) will be the inside ambient temperature of your fridge.
  • Of course, the better the quality of the thermometer, the more accurate the temperature will be. I place my traceable thermometer inside and compare it to the cheaper indoor/outdoor temperature. In my case there is a two degree difference. I just keep that in mind when I monitor the temperatures.
  • Your local homebrew supply store will probably have the stick-on thermometers you can use for your fermenter. It’s not the most accurate instrument but is better than nothing.
  • A good option is a liquid-filled thermometer that you place inside the fridge. The liquid reacts much slower to changes in ambient temperature than does the air inside the fermentation fridge. If you have the door open for a short period of time, while measuring the SG of your fermenting wort for example, the liquid filled thermometer will still measure the same temperature. It is also a little more accurate measuring the fermenting beer than just a typical thermometer, since it is filled with liquid just like the fermenter is.

Controlling Fermentation Temperature

Once you can monitor fermentation temperatures, here are a few solutions for controlling the actual temperature of your fermentation:

Refrigerator or Freezer The most common solution is the spare refrigerator or chest freezer for fermentation temperature control.  Because fermentation temperatures need to be more precise than the refrigerator can provide, you will need to bypass the thermostat. The simplest way is to use either an analog or digital electronic thermostat controller.  

The only downside to using a spare fridge or freezer for fermentation temperature control is when you also use it to store your bottled beer. The temperature inside is always fluctuating based on whether you are fermenting an ale or a lager. Aging beer benefits from stable temperatures. I’m not sure what effect this has on the beer’s quality. It may be minimal for beers you will consume within a few months. But for big beers meant for long aging, like barleywines, lambics, and old ales, the consequences of constant temperature fluctuations may be more dramatic. More research is in order.

Fermentation temperature controllers recommended:

INKBIRD ITC-308;

INKBIRD ITC-308-WIFI;

Souce: winning-homebrew website.

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