Lager Temperature Control Tips For Homebrewing

by Dane Wilson | Last Updated: October 31, 2022

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Brewing lagers but can’t quite control the temperature? Sounds like a problem. After all, a decent lager is one that has been cold conditioned for a period of time. Otherwise, you won’t get the clarity you obviously want. Lager temperature control can be difficult, whether you have been brewing beer at home for years or have just started out.

That is why this article is going to go over some of the tried and true lagering temperature control tips, so your lager comes out as crisp and delicious as it should. Let’s get started.

Table of Contents

• What is a Lager?
• About Lager Fermentation
• Why Do Lagers Need Cold Fermentation and Conditioning?
• What Happens If I Brew a Lager at Too Warm a Temperature?
• What Happens If The Lager is Too Cold?
• Controlling the Wort Temperature
• Maintaining Lager Temperature During Fermentation
• Pitching Your Yeast
• Controlling Lager Temperature During Cold Storage
• Lager Temperature Control With Refrigeration
• Can I Use a Freezer For Cold Conditioning?
• Making Your Own Brew Belt
• You’re In Control Now

What is a Lager?

Before getting into lager temperature control, it is imperative that you receive a crash course in lager beer. What is it, why is cold fermentation important, and so on. A lager is the second main type of beer, meaning that it is not an ale. Lagers and ales are different in many ways, including how they are fermented. For lagers, the majority uses a bottom-fermenting yeast and cold conditioning.

Cold conditioning is incredibly important to making lagers, well, lagers. In fact, the word “lager” is German for “storage,” which is why you have to know how to lager the lager in the lager if you want a good one. Got it?

Many of your favorite beers are lagers, by the way. Miller, PBR, Budweiser, Busch…even those exceptional dunkels, bocks, and Oktoberfest brews are lagers.

Check out this video which discusses the art of lagering for some more inspiration:

About Lager Fermentation

If there is one thing you need to know about lagers, it is that their bottom-fermenting yeast, Saccharomyces pastorianus, prefers the cold. The temperature at which beer ferments and conditions (in the case of lagers) is essential to the quality of the final result. Ale yeasts generally ferment between 60-78°F (15-25°C). Meanwhile, lagers will ferment between 48-58°F (8-14°C).

After primary fermentation, lagers are then placed into something called cold conditioning for another 2-3 weeks. The temperature during cold conditioning is often freezing (32°F or 0°C).

Why Do Lagers Need Cold Fermentation and Conditioning?

To understand why cold fermentation is required for nearly all types of lagers, you have to first understand how the yeast reacts to such temperatures. In general, yeast causes fermentation by consuming sugars present in the wort. As they eat the sugar, the yeast cells release carbon dioxide and other compounds that make alcohol and flavor in the beer. At room temperature, yeast tends to feast on the sugar rapidly, releasing an explosion of CO2 and other compounds.

On the other hand, with cold fermentation, the yeast is much more slow and deliberate. Any byproducts are produced at a slower rate, which leads to fermentation taking longer. The result is that lagers tend to have far less alcohol than ales and much less haze.

Without cold fermentation and conditioning, lagers would not have their characteristic crispness that has made them popular throughout the world.

What Happens If I Brew a Lager at Too Warm a Temperature?

Lager temperature control is essential. Here are some things that could happen if your lager accidentally got too warm during brewing, fermentation, and conditioning:

• Off flavors from fusel alcohols and esters start to appear in the brew as the activity of the yeast accelerates. Keep in mind that some flavors are not off-putting, but they are not appropriate for the beer style.
• Yeast consumes the sugars too quickly, resulting in a failed fermentation and less than stellar beer.
• The yeast, which is generally happy in the cold, gets stressed out from the heat and starts to die off, leaving you with incomplete or unsatisfactory fermentation.
• Poor temperature control often leads to the yeast succumbing to alcohol toxicity.
• Yeast metabolism also generates heat, which could, in turn, be problematic for a batch of beer that is already too hot. Worse case scenario, the yeast dies off quickly, leaving the beer unfinished.

What Happens If The Lager is Too Cold?

Although yeast for lagers is well adapted to the cold, that does not mean it can handle poor temperature control. Even cold-loving yeast will exhibit stress in freezing conditions. Here are some problems you can expect if your lager gets too cold:

• Fermentation may never begin.
• Your yeast may be sluggish in the beginning, which leads to primary fermentation kicking off too late and too slow.
• Fermenting too cold can lead to poorly developed flavors.
• Bacteria may have a chance to take over the brew, should there be any contaminants in the wort or fermentation chamber.
• When fermentation does finally commence, the CO2 will be trapped within the cold beer. The right temperature range is required for gassing off the beer. If carbon dioxide is not adequately removed, you may get some off-flavors, including that of sulfur. Yuck.

So how do you keep the lager temperature controlled from start to finish?

Controlling the Wort Temperature

The first part of brewing of lager where you need to be worried about temperature control is when chilling the freshly boiled wort. Prior to pitching the yeast, the wort has to be the correct temperature. Most lager strains will happily get to work between 48-55°F (9-13°C), but there are exceptions to that rule:

• Wyeast 2124 Bohemian Lager: 68°F (20°C)
• White Labs WLP810 San Francisco Lager: 65°F (18°C)
• Wyeast 2035 American Lager: 58°F (14°C)
• White Labs WLP862 Cry Havoc: 58°F (14°C)

Most of the time, an ice bath is going to work splendidly. Sometimes, though, it is not going to do the work quickly enough. For that, it is recommended you get an immersion chiller, which can get the temperature down to 50°F (10°C) in a matter of moments without getting too cold. Plate chillers are also a great way to cool the wort effectively, especially when contending with summertime heat.

Maintaining Lager Temperature During Fermentation

Once you got the wort chilled enough for fermentation, you may be wondering how to keep the temperature level. The best solution is not a standalone fermentor but a fermentation chamber that comes with a built-in chest freezer or refrigeration function. On the outside, you will have a thermostat or temperature controller that allows you to fine tune the brew’s temperature without fail.

Digital controllers make it easy to maintain the temperature throughout the entire fermentation process. Plus, you can also raise the temperature in a blink to perform a diacetyl rest right at the end of primary fermentation. The initial financial investment of such a fermentation chamber is not much. Some models are available for US$50 while others go for around US$120.

It is also recommended that you use a sterilized thermowell, or a waterproof tube that can be inserted into the wort to monitor the temperature. Keep in mind that yeast generates around 2-4°F (1-2°C) of heat when metabolizing the sugars.

Pitching Your Yeast

Many homebrewers make the mistake of lowering the wort to around 65°F or 18°C and then pitching the yeast. However, if you stabilize the temperature there and do not account for the metabolic heat given off by the yeast, it could cause the wort’s temperature to increase, leading to more esters in your beer. That is why it is recommended to get the wort to a temperature cooler than the ideal fermentation temperature, pitch the yeast, and let the heat from yeast metabolism bring it up to where it needs to be.

Why is this important? Because yeast growth during the first few days of fermentation is important to creating a clean, crisp profile.

Again, this can all be easily down with a fermentation chamber that is refrigerated to some degree. Digital overrides for the refrigerator can be purchased online, making it easier to control the internal temperature of the chamber. These are fairly easy to set up as well.

The video below gives you some visual instructions on how to set up a refrigerated fermentation chamber:

Controlling Lager Temperature During Cold Storage

The lagering process of brewing a lager is where the magic happens. Cold storage is required for at least 2 weeks, but some breweries have gone longer than 4 weeks. In cold storage, the lager loses any lingering diacetyl, sulfur, and other undesirable flavors. The lager flavors also mature, resulting in a better tasting brew.

Ideally, you want the cold storage temperature to be between 32-36°F (0-2°C). Prior to lagering your beer, lower the temperature of your fermenting beer (or finished product) by 3-5°F (2-3°C) every day leading up to cold conditioning. This generally takes about a week. Once that happens, you can remove the wort from the primary fermentation chamber and put it into cold storage.

Why do you want to reduce the temperature little by little over the course of a week? To prevent the yeast from getting shocked and calling it quits when there is still work to do.

For cold storage, you can use a kegerator or a corny keg. Considering the latter first, it is an ideal lagering vessel, because you can purge it easily. Corny kegs are resilient even in freezing temperatures. Digital kegerators, however, make it easy to control the temperature.

Lager Temperature Control With Refrigeration

Much of the above mentioned tips assume you have some refrigeration and digital temperature control. Does that mean you are doomed without it? No! Even if you lack equipment, you can still make a delectable, crisp lager. First, you will need to chill the wort as you usually would. Again, immersion, counterflow, and chilling plates are going to work best for you. Anything with digital temperature control can stabilize the temperatures and increase your chance of success.

Grab a thermometer so you can ensure that the temperature of the wort is ideal before pitching the yeast.

If you do not have a refrigerated area or basement for fermentation, put the fermentation chamber in a large tub and set it up in the coolest place in the house. Fill the tub with cool water and use ice packs or frozen bottles of water to cool the water surrounding the fermentation vessel.

Put a thermometer in the water in the tub and routinely check the lager temperature within the fermentor.

If the temperature continues to fluctuate, put a wet shirt or sheet over the fermentor or carboy and switch on an oscillating fan. This is known as the swamp cooler method, it is highly efficient. If you are routinely changing the ice packs and using the shirt, you could effectively reduce the temperature by 10°F (6°C).

Can I Use a Freezer For Cold Conditioning?

You can certainly use a freezer to aid in lager temperature control. However, you should not put your temperature probe or thermometer inside the fermentor. Even inside the freezer, there is a heat transfer between the beer and the air inside. The temperature of the freezer could drop to -20°F (-29°C) before the fermentor even reaches 55°F (13°C). Instead of rushing it, equalize the temperature of the freezer with that of the beer. Be patient with this part.

Similarly, since the walls of the freezer can get extremely cold, it is recommended that you put some kind of buffer between the fermentation chamber and the freezer. A 2×4 plank of wood, for example, can get the chamber away from any surfaces within the freezer that could affect the internal temperature and upset fermentation.

Making Your Own Brew Belt

Let’s say you are trying to brew a lager during the winter and the space where you usually cold condition your beer is absolutely glacial. What do you do then? If you need to heat things up a little, you could purchase a nifty gadget called a Brew Belt, which is similar to a heating pad for your fermentation chamber. The Brew Belt maintains an even temperature for as long as necessary. You can also move the Belt up and down the fermentor for additional control of where the heat goes.

Keep in mind that Brew Belts are not to be used on glass carboys.

Now, if you do not want to fork out money for the Brew Belt, you could rig up something similar on your own. Using an electric blanket, you can drape it around the fermentation chamber. This will also work by clothing your fermentor in an old shirt or sweater and blowing on the fabric with a space heater.

Keep a thermometer strapped to the outside of the fermentor and check it regularly. It may be a bit harder to monitor the temperature with the DIY Brew Belt method.  

You’re In Control Now

Controlling lager temperature during the fermentation and cold conditioning phases can be difficult, especially when you don’t have the technology to make it easier. Digital temperature controls will give you the peace of mind you need, but you can also utilize cool basements, ice baths, swamp coolers, and other methods to reduce the temperature and make your brew a success. Which tip are you going to try first? Are there any we accidentally left out? Let us know!