Lagering: What It Is, Temperatures, How Long, and How to Do It at Home

Lagering is the cold conditioning stage that gives a lager its clean, crisp finish. The word comes from the German lagern, to store, because for centuries the only way to do it was to leave beer in a cold cave for the winter. Today it means holding finished beer near freezing for weeks so the yeast tidy up after themselves and everything that causes haze and rough edges drops out.

This guide covers the whole lager process, from fermentation temperature through the diacetyl rest to cold conditioning, how long each stage takes, and the equipment that makes it possible at home. It ends with the fast method most small breweries use now.

What lagering actually does

Four things happen in a cold tank over several weeks:

• Yeast finish their cleanup. Diacetyl (butterscotch) and acetaldehyde (green apple) are reabsorbed by yeast that are still slowly active in the cold.
• Sulphur compounds leave. Lager strains make more sulphur than ale strains. Over weeks it dissipates, especially if the beer is under a little pressure and vented occasionally.
• Haze drops out. Cold makes proteins and polyphenols clump together (chill haze) and settle, along with the yeast. The beer becomes bright without filtering.
• Flavour rounds off. Harsh hop bitterness softens, malt flavour comes forward, and the beer tastes integrated rather than sharp.

None of that happens quickly at cellar temperature, and none of it happens at all if the beer is warm. That is why lagering is really a temperature-control problem.

The three stages and their temperatures

Stage	Temperature	How long	What is happening
1. Primary fermentation	48 to 55°F (9 to 13°C)	7 to 14 days	Yeast convert sugar to alcohol, slowly and cleanly
2. Diacetyl rest	Raise to 60 to 65°F (16 to 18°C)	2 to 3 days	Yeast reabsorb diacetyl and acetaldehyde
3. Lagering (cold conditioning)	30 to 35°F (-1 to 2°C)	3 to 8 weeks	Sulphur leaves, haze and yeast settle, flavour rounds

Drop from stage 2 to stage 3 gradually, about 5°F a day, or crash straight down once you are sure fermentation is complete. Either works; the gradual drop is gentler on yeast you want to harvest.

Lagering temperature

As close to freezing as you can hold without freezing the beer. 32 to 34°F is ideal; 35 to 38°F still works and takes a little longer. Beer with 5% alcohol freezes at about 28°F, so there is a margin, but a tank against a chiller coil can freeze at the wall. A jacketed tank with glycol at 28°F and the beer set to 33°F is the stable way to do it.

How long to lager

The old rule was a week for every 10 points of original gravity, so a 1.048 pilsner gets five weeks and a 1.070 doppelbock gets seven. It still holds up. In practice:

• Light lagers, pilsner, helles: 3 to 5 weeks. They have nowhere to hide, so give them time.
• Amber and dark lagers, märzen, dunkel, bock: 4 to 8 weeks.
• Doppelbock, baltic porter, eisbock: 8 weeks to several months.
• Pressure-fermented lagers (below): 1 to 2 weeks is often enough, because most of the cleanup already happened warm.

Taste it weekly. When the sulphur is gone and it is bright, it is done. Longer is rarely worse, but it is not always better either.

What you need

The hard part of lagering at home is not the recipe, it is holding a tank at 33°F for a month in a house that is 70°F. Three ways to do it:

1. A fridge or keezer with a temperature controller. Cheapest. Limits you to a vessel that fits in a fridge, so 5 to 6 gallons, and you lose the fridge for a month.
2. A jacketed fermenter on tap water. Works for the fermentation and diacetyl stages in a cool basement. Tap water is rarely under 50°F, so it cannot lager.
3. A jacketed fermenter with a glycol chiller. The way breweries do it. A Unitank with a temperature control kit and a compact glycol chiller holds any temperature from 28 to 75°F, at any size from 8 gallons to a barrel, and the same chiller runs two tanks so you can lager one while fermenting the next. Sizing a glycol chiller has the numbers.

The traditional method, step by step

1. Chill the wort to 45 to 48°F, below your fermentation temperature, and oxygenate well. Lager yeast need more oxygen and a bigger pitch than ale yeast: roughly double the cell count.
2. Let it rise to 50 to 52°F and hold. Fermentation starts slowly; 24 to 48 hours before visible activity is normal.
3. When gravity is about half to two-thirds of the way to terminal (a 1.048 beer at around 1.020), raise to 62 to 65°F for the diacetyl rest. Hold 2 to 3 days after you reach terminal gravity.
4. Cool to 33°F over a few days. If your vessel can hold pressure, set a spunding valve to 5 to 10 psi so the tank stays positive as it shrinks and no air gets drawn in.
5. Lager 3 to 8 weeks. Dump yeast from the cone once a week if you have one.
6. Transfer to a keg under CO2, carbonate, and serve. Or let the spunding valve carbonate it in the tank during lagering.

The fast method: pressure lagering

Most small breweries no longer ferment lagers cold for two weeks. They ferment warm under pressure, which suppresses the esters that warm fermentation would normally produce, then crash and lager briefly. The result is very hard to tell from the traditional method, and it is done in two weeks instead of six.

1. Pitch at 55°F, let it rise to 62 to 65°F.
2. After 24 to 48 hours of open fermentation, set the spunding valve to 12 to 15 psi.
3. Ferment to terminal, 5 to 7 days. The diacetyl rest happens on its own because the beer is already warm; hold 2 more days at terminal.
4. Crash to 33°F with the valve still set.
5. Lager 7 to 14 days, dump yeast, transfer.

Everything about this method depends on a vessel that holds pressure and a jacket that holds temperature. The pressure fermentation guide covers the how and why in detail.

Mistakes that ruin lagers

• Underpitching. The most common cause of a slow, sulphury, diacetyl-heavy lager. Make a big starter or pitch two packs.
• Crashing too early. Cold stops the yeast before they clean up. Confirm terminal gravity on two consecutive days first.
• Skipping the diacetyl rest. Butterscotch does not lager out by itself at 33°F. Do the rest warm, before the crash.
• Air during the crash. A cooling tank pulls air in through an airlock. Use a spunding valve or a CO2 blanket.
• Temperature swings. A fridge cycling between 30 and 40°F is fine. A garage swinging between 40 and 70°F is not. If you cannot hold it, you cannot lager.

Lager vs ale, briefly

Ale yeast ferment warm (62 to 72°F) and fast, and produce esters that are part of the style. Lager yeast ferment cold and slow, produce few esters, and need the cold conditioning to finish. The yeast decide the process; the process decides the flavour. If you want the long version: ale vs lager fermentation, and for the beer itself, pilsner vs lager.

Ready to brew one? Brewing a pilsner, step by step. And if you are deciding whether a jacketed tank is worth it for lagers: ask us, we brew them.