Some brewers refer to the entire process of brewing a lager as "lagering", which can be confusing. The term lagering actually refers to the extended secondary aging the beer undergoes at cold temperatures (hovering above freezing), sometimes referred to as cold conditioning. While this step is necessary for brewing a proper lager, ales can also benefit greatly from cold conditioning, or lagering. First we'll talk about the equipment and processes needed to brew a lager, followed by the finer points of lagering.
How is lager yeast different?
Lager yeast differs from ale yeast in that it is a bottom fermenting strain. This simply means that when the yeast is engaged in anaerobic fermentation it tends to congregate closer to the bottom of the vessel. Lager yeast is notorious for producing markedly lower ester and diacetyl levels, resulting in a beer with a very clean finish. Different strains of lager yeast produce different levels of sulfur compounds, but all tend to dissipate during the lagering process. Lager yeast strains generally enjoy an optimum fermentation temperature range between 45-55°F with some exceptions.
It is very important to note that the primary fermentation of lagers will take much longer than ales. The fermentation does not look the same as an ale either, it will be very slow. The other thing to note is the overall amount of time it takes to make a lager. You are usually looking at 3-6 months before your lager is done. This is mainly due to how the yeast uses the sugars to create alcohol, so do not rush the process. Most people consider lagers more mellow than ales, so keep that in mind.
The beer just likes to chill!
You can use a basement floor, which could be a little warm, but may work. Just make sure that the floor stays a fairly constant temperature. You do not want your beer to change temperatures throughout the day. Significant temperature changes (more than 5 degrees a day) can stress the yeast. Simply place a glass of water on your basement floor and put your dial thermometer in it. Check it the next day–if the temperature reads between 45 and 55ºF, you're ready to lager! The ideal temp for most lagers is 52°F, but some styles' might be a little lower or higher. This is why Midwest recommends you have a controlled environment throughout the lagering process. Most brewers will use a refrigerator with an outside temperature control unit. This will allow you to control the temperature of the refrigerator to within a few degrees. 48°F is a good setting for most lagers; consult your recipe and/or yeast package. Now let's get ready to brew!
2 days before you brew: Stabilize the fermentation environment
Before the brewing process has begun it is a good idea to prepare your fermentation environment a few days in advance to allow it a chance to stabilize. If you are intending to ferment your lager at a temperature of 48°F, dial that temperature in on your thermostat a couple days before you begin to allow your refrigerator a chance to stabilize at this temperature.
1 day before you brew: Make a yeast starter
A yeast starter is a good idea for your lager; a 2 L starter for 5 gallons of wort or a 4 L starter should be fine for 10 gallons of wort. You should prepare your yeast starter the day before you plan to brew. Your starter should be at the peak of its fermentation cycle within 24-36 hrs and this would be the optimum time to use it. Once your yeast starter is made, put it in your 48°F environment to stabilize overnight.
Pitching the yeast starter
Once you've boiled, chilled, and aerated your wort, you'd think it would be time to pitch that big yeast starter you made, but hold on! There are a few schools of thought about this step; we'll share these three methods along with our recommendation as to which method we feel works best.
- Method one: Room temperature until you start seeing bubbles. You can pitch the yeast starter into the primary and leave it at room temperature until you see signs of fermentation, then remove it to the controlled environment. This method will get the yeast into active fermentation faster, but will result in more ester production and a less-clean tasting beer.
- Method two: Stick it in the fridge. You can pitch the yeast into the primary and then immediately put it into the controlled environment. As with method one, a similarly adverse effect can occur. With most tap water driven chillers, the wort is chilled to roughly 65-75°F, depending on the season and the current groundwater temperature. This is quite a bit higher than the temperature the yeast starter had been stabilized at, and shock can come into play along with off flavors.
- Method three: Just chill, baby! You can place the primary into the controlled environment and let it stabilize for 24 hours before pitching the yeast. This is the method Midwest recommends, for a couple of reasons:
- The yeast is pitched into the environment it has already been fermenting in
- You should observe decreased lag time and decreased production of undesirable flavors
- If you are going to leave wort without pitching adequate amounts of yeast until the wort gets to pitching temperature, you MUST make sure everything in contact with the wort is sanitized! The extra time gives any other resident microbes a head start.
Alternately, some brewers will pitch their yeast when the wort is warmer and slowly lower the temperature of the fermenter gradually over the course of several days until they have reached the optimum temperature for their yeast strain. This method works, but tends to produce more diacetyl (a buttery-flavored ketone) than method three. As the temperature drops, the yeast become less active and are less inclined to consume the diacetyl that was initially produced. The result is a buttery/butterscotch flavor in the lager, which is completely out of style. Some amount of diacetyl is considered good in other styles, such as dark ales and stouts, but is considered a flaw in lagers.
The diacetyl rest
To remove any diacetyl that may be present after primary fermentation, a diacetyl rest may be used. This rest, at the end of primary fermentation (when your gravity is 10-15 points away from your target final gravity), consists of raising the temperature of the beer to 55-60°F for 24-48 hours (some brewers will simply put their fermenter at room temperature, which will work) before racking it and then cooling it down for the lagering period. This makes the yeast more active and allows them to eat up the diacetyl before downshifting into lagering mode. Some yeast strains produce less diacetyl than others.
Pitching sufficient quantities of yeast under the correct conditions should allow you to wrap up the primary fermentation in 10-21 days, depending on the style beer being brewed and/or the yeast that was pitched. The beer can then be transferred to the secondary and allowed to finish up for another 7-14 days. When the beer is entirely finished fermenting it may be racked again (optional) and the temperature dropped to 33°F. The lagering process has begun and can continue anywhere from two to six months.
If you're bottling and not kegging
If you want to bottle the beer before beginning the lagering process, you can do so out of the secondary after a few weeks has passed and much of the yeast has settled to the bottom. Bottle as you normally do, then return the bottles to the controlled environment (at the temperature you performed the primary fermentation at) until properly carbonated. This should take roughly two weeks but may take longer, depending on the style.
Removed from the primary yeast sediment and allowed to chill and age, the beer should clear quite well. Sulfur and other various extraneous aromas and flavors dissipate until it achieves that clean character for which lagers are known. As the saying goes, time heals many wounds. A number of the haze problems sometimes associated with ales are conspicuously absent from most lagers, mainly due to the time spent lagering. Some brewing texts recommend slowly reducing the temperature by no more than 5°F per day until the temperature is at the desired setting for lagering. However, many homebrewers ignore this advice and achieve excellent results. There is agreement that in order to achieve the maximum effect the lagering needs to be done cold, with the temperature no more than 40°F. Many commercial breweries lager at nearly freezing temperatures, in the 32–34°F range.
How long to lager is a matter of some discussion. Light American lagers are typically held near freezing for 10–20 days, while some strong German doppelbocks are lagered as long as six months. For medium to high-gravity beers, Greg Noonan — brewpub owner and author of "New Brewing Lager Beer" — recommends 7–12 days per each 2°Plato of original gravity. (One degree Plato is roughly equal to 4 specific gravity "points."). For lower gravity lagers the time is reduced to 3–7 days. According to those guidelines, a 1.064 O.G. German bock should be lagered for 112–192 days, while a 1.040 American lager would be lagered 15–35 days.