What Happens If Your Beer Fermentation Temperature Is Too High?

You’ve probably heard guidance about finding the optimal fermentation temperature for the beer you’re brewing. But controlling temperature can be hard. What happens if you ferment your homebrew at temperatures that are too high?

Fermenting at too high of a temperature is unhealthy for yeast, leaving your beer susceptible to the development of off-flavors from undesirable elements. If the temperature becomes exceptionally high, it can even kill your yeast. Your target temperature will vary depending on the type of yeast you use and the style of beer you’re brewing.

Read on to find out more about why temperature control is so important, and what you can do about it.

What happens if you ferment your beer too hot?

Depending on where you store your fermenting beer, its temperature can be tricky to control. For best results, it’s crucial to maintain your beer’s optimal temperature, from the moment you pitch your yeast through the remainder of fermentation.

If your beer gets too hot during fermentation, it can affect the final product of your homebrew with unwanted flavors, sometimes quite severely. Yeast is very finicky and highly affected by both high and low temperatures.

This is why most brewer’s yeast on the market comes printed with recommended fermentation temps for best results. Always read and follow these guidelines when brewing.

How does temperature affect beer fermentation?

If the temperature in your fermenter is too low, fermentation will slow greatly or even stop entirely. When fermentation stops before all of the available sugars have been converted, homebrewers call the beer “stuck.” If you suspect your homebrew has become stuck, move the fermenter to a room temperature area and monitor closely for additional activity.

High temperatures, on the other hand, can create a host of problems, here are a few key things to watch out for:

  • Fusel Alcohol – Warm temperatures can cause yeast to produce more fusel alcohol, an extra-harsh form of alcohol that may present itself as a burning sensation when you taste your beer. It’s often likened to cheap liquor and will overpower the flavor of your beer’s key ingredients.
  • Acetaldehyde – Warm yeast also can promote the development of additional acetaldehyde. This naturally occurring compound is present in trace amounts as part of a normal fermentation, but too much of it can lead to flavors of green apple in your brew. 
  • Rapid Fermentation – The higher the temperature, the faster your fermentation will go. A couple of degrees is nothing to be concerned with, but if your beer develops too fast you run the risk of off-flavors. Good things come to those who wait!

Why is fermentation faster at higher temperatures?

Warmer conditions make fermentation go faster, but why?

Heat is a catalyst in the sense that it causes the particles in beer to become more active and move faster. The warmer your beer, the faster the yeast will consume the sugars and convert them into alcohol and CO2

Bear in mind that speeding up fermentation aggressively is typically not optimal, but you can make a small difference in your fermentation time by keeping your fermenter at the higher end of your particular yeast’s target fermentation temperature range.

Does fermentation increase temperature?

Many homebrewers overlook the fact that the fermentation process itself generates heat.

Because of the heat produced by fermentation, you should plan for the temperature in your fermenter to become at least 5°F (15 °C) higher than the ambient temperature. 

Much like our bodies when we exercise, the temperature of yeast increases with activity. If you start your yeast at too warm a temperature, your beer can end up reaching dangerously warm temperatures

What happens if you pitch yeast too hot?

Many beginning homebrewers make the mistake of getting impatient waiting for their wort to cool and pitching their yeast when it’s too hot.

Pitching yeast into a hot wort can be a critical error as the high temperatures can kill some or all of the yeast. Keep in mind that your wort was recently boiling and even if it doesn’t seem that warm on the surface, it takes a very long time for the whole batch to cool down.

Some homebrewers turn to tools for cooling beer fast. Investing in a wort chiller is a simple and relatively affordable way to speed up your brewing process and keep your yeast safe.

Wort chillers work by connecting straight to your sink. By running cold water directly from your sink through the copper tubing, you can keep the copper consistently quite cold as you dip it into your wort. Because of the conductive qualities of copper, it remains cool even when dipped in warm wort as long as cool water is running through it. This technique cools the wort much faster than waiting for it to cool on its own at room temperature.

What temperature will kill yeast?

Different strains of yeast thrive in different temperatures.

Anything over 100°F (38°C) is generally in the warning zone for yeast. Temperatures of 120°F (49 °C) will begin to consistently kill off yeast and once you reach 140°F (60 °C), most yeast can no longer survive.

If you’re concerned about the health of your yeast, monitor your airlock regularly for bubbles. They should begin to appear about 24 hours after pitching the yeast. If, after a few days, no bubbles appear in the airlock, your wort may have been too hot during pitching.

What’s the best temperature for beer fermentation?

There’s no single temperature that works for all styles of beer and yeast, so always check your recipe as well as your yeast package for temperature guidelines. 

North Slope Chillers offers this helpful chart of Ale and Lager yeast temps.

In general, ales should almost always be fermented at higher temperatures than lagers. Ales tend to thrive right at room temperature: between 65°F (18°C) and 74°F (23°C). Lagers, on the other hand, need to be kept much cooler, at more like 48°F (9°C) to 60°F (16°C). 

If you’re new to homebrewing, I recommend starting with an ale. They tend to do well at about room temperature and, assuming your space remains consistently at that temperature, should not require any maintenance or temperature control during fermentation.

How to control fermentation temperature

Maintaining a consistent fermentation temperature can go a long way toward producing the best beer possible, but how can you ensure a stable temperature when you’re homebrewing?

To control your fermentation temperature:

  • choose a fermentation spot with consistent ambient temperature
  • stay cool with a cool wrap
  • warm your beer when it gets cold
  • maintain a good temperature once you reach it

Choose a Fermentation Spot With Consistent Ambient Temperature

Because of climate control in our houses and apartments, we can forget just how much the temperature really can fluctuate.

Even if your fermenter is in a temperature-controlled closet or spare room, make sure it’s not in a spot where a vent will be blowing either hot or cool air directly on it. By the same token, avoid storing your fermenter near an open window where direct sunlight or drafty air may affect it while you’re away.

Places like garages and basements may seem like great spots for fermentation during the day, but don’t forget that temperatures tend to drop in these spaces at night. 

Stay Cool With a Cool Wrap

If your house runs warm in the summer, you may need to explore options for keeping your fermenting beer slightly cooler than the air around it.

Handle warm spells by simply wrapping your fermenter with a cool, wet towel and switching it out throughout the day. 

For more extended warm periods, try keeping your fermenter in a tub of cool water. Beware of adding ice to the water as you don’t want to chill your beer too much.

Reaching your optimal fermentation temperature may take some trial and error with this method, so plan to monitor closely.

Warm Your Beer When It Gets Cold

If you must keep your fermenter in a cool place, you may need to warm it slightly, especially if you’re brewing an ale.

A simple space heater can make a big difference in a drafty basement but beware, you don’t want to leave warm air blowing directly onto your fermenter. Keep it across the room so it warms the air in the room without getting the fermenter too hot.

If a space heater isn’t an option, sometimes just wrapping your fermenter in a blanket or even a cool weather sleeping bag does a good job of keeping its heat contained without exposing it to the chilly air.

Maintain a Good Temperature Once You Reach It

If you have access to a large cooler or even an old, powered-down minifridge, these can be good options for keeping your fermenting beer completely sequestered from ambient air. 

These can be a great resource for maintaining a good temperature of your beer once you reach it, but keep in mind that fermentation will naturally create a bit of heat so as usual, keep a close eye on your beer as it ferments.

Otherwise, you run the risk of the heat naturally developed during fermentation becoming trapped in the insulated device and warming your beer too much.