Lagering at Cellar Temperatures

The textbook answer to a question about the traditional lagering method is that lager beers are fermented at temperatures ranging from 46–54 °F (8–12 °C), often in open fermenters, until beer is about 2 °Plato (8 gravity points) above the anticipated end point, racked to a lagering vessel equipped with a spunding valve to allow control of pressure developed during the end of fermentation, and allowed to slowly cool to about 32 °F (0 °C). A general rule for the duration of lagering is one week per degree Plato (4 gravity points) based on wort strength prior to fermentation. In the past, standard strength Pilsners at 12 °Plato (1.048 SG) lagered for three months and bock beers at 16 °Plato (1.065 SG) received the four-month treatment.

Closed fermentation vessels, the advent of commercial refrigeration, the development of the unitank process, better understanding of brewing biochemistry, beer filtration, the widespread use of chill-proofing brewing aids, and brewing economics are some of the things that led to changes in today’s approach to lagering. A key part of any process change is to understand the objectives of the process. In the case of traditional lagering, I believe there are three primary changes that must be preserved by alternate methods: 1) flavor maturation, 2) beer clarification and haze stabilization, and 3) carbonation. Traditional lagering, and cask ale production as a related topic, accomplishes these objectives.

A common change among lager brewers is to allow the fermentation to naturally warm towards the end of fermentation to accelerate the conversion of alpha acetolactate excreted from cells during fermentation into diacetyl. Yeast cells then absorb diacetyl and acetaldehyde and reduce these aromatic, “green beer” compounds into flavor-neutral acetoin and ethanol. This simple process change speeds up flavor maturation and is used to reduce the total time required for lagering. Although there are other flavor changes that occur during lagering, like reduction in volatile sulfur aromas and bitterness accompanying beer clarification, diacetyl and acetaldehyde reduction are the most significant and tend to dominate what brewers think about in terms of flavor maturation.

Extended aging, especially in relatively shallow horizontal lagering tanks, results in naturally clear beer. For whatever reason, the use of isinglass finings was not widely used by lager brewers, and lager brewers relied on time and cold temperatures to clarify beer. The cold temperature part of the equation is important because chill haze particles formed upon beer cooling do eventually settle. Lager brewers did, however, use other tools, like tannin powder from oak galls, to help clarify beer. In fact, Anheuser-Busch used oak gall tannin powder in so-called schoene (pronounced shay-na) tanks up until the turn of this century. Commonly used chill-proofing agents today include a variety of silica gels, PVPP, and the enzyme Aspergillus niger prolyl endoprotease (AN PEP), often referred to by the trade name Brewers Clarex®. Silica gels and AN PEP work by removing haze-active proteins and PVPP does its thing by removing haze-active polyphenols. These tools all shorten process time. And AN PEP allows brewers to chill-proof beers without having to chill it, saving time and energy.

Beer can be chill-proofed without being clarified. Commercial lagers brewed by large breweries are typically clarified by centrifugation and/or filtration, while smaller breweries without clarification equipment often rely on silicic acid fining solutions, such as Kieselsol or Biofine Clear, to quickly settle yeast from beer upon chilling to ~32 °F (0 °C). Filtration was first used by breweries in the late 1800s to produce brilliantly clear beer without the added costs of extended storage. 

Carbon dioxide is “free” to brewers who naturally carbonate, and large breweries continue to take advantage of carbon dioxide produced by yeast for beer carbonation. None of the time-saving methods discussed thus far interfere with natural carbonation. To capture this gas, lagering tanks must be pressure-rated for the combination of pressure and temperature required to produce beer containing about 5.4 grams or 2.7 volumes of carbon dioxide. Because lager yeast function well at cool temperatures, fully carbonated lager beer can be produced at pressures less than 1 atmosphere, aka 1 bar or 14.7 PSI, of gas pressure. Ale yeast, however, typically have difficulty fermenting when the temperature drops below 60 °F (16 °C) and require at least 1.7 bar/25 PSI pressure for carbonation. This is a big deal to commercial breweries because most countries have very different design codes for vessels designed and rated for use at pressures above 1 bar. In practical terms, this means most ales carbonated to lager-like levels are carbonated by bubbling carbon dioxide into beer.

OK, time to wrap this information into a homebrewing solution. You don’t need to cold age your beer for long if you adopt these modern methods and use your chilly basement to your advantage. Start by cooling your wort down to about 50 °F (10 °C) because I do want to maintain some aspects of traditional lager production with this recommendation. Fermenting lager at 52 °F (14 °C) is relatively normal, so just use your basement environment for fermentation. If it’s relatively easy to move your fermenter into a warmer room, consider moving it towards the end of fermentation to speed up diacetyl and acetaldehyde reduction. I am a fan of aging under pressure developed by fermenting yeast and suggest spunding your fermenter or racking your beer into a keg if fermenting in a vessel not rated to hold pressure (read this issue’s “Techniques” found here).

It’s now time to allow for carbonation to develop and for your beer to gravity sediment. It’s perfectly acceptable to bottle your beer at this point and finish lagering in the bottle. One major downside to this is that you may end up with more sulfur notes in your beer than if you lager in a keg. I’ll just leave this topic for you to ponder and will continue this discussion from a bulk-lagering perspective.

Your basement is the perfect lager cellar for the carbonation step. Make sure to locate your unitank/pressure fermenter or lagering tank/keg in a spot where it can sit undisturbed for 3–4 weeks. During this time, yeast will consume the last bits of fermentable extract (assuming that you capped your fermenter or racked before fermentation ended), excess pressure will be vented along with sulfur aromatics from the spunding valve, and yeast will settle from the beer as activity ceases. If your fermentation finishes before spunding, adding priming sugar before aging works perfectly if you plan on serving your lager from a keg or have a counter-pressure bottle filler. 

At the end of the 3–4 week lagering phase at 54 °F (14 °C), your beer has undergone diacetyl and acetaldehyde reduction (with or without the room temperature rest), carbonation, and most of the yeast has settled out of the beer. You’re 90% complete and have yet to need a refrigerator. At this point, you can chill your beer and serve from a keg or bottle if you have the right equipment (or chill and drink the bottles if you have lagered in the bottle). The problem is that as soon as you chill your gravity-clarified, cool-lagered beer, it is going to instantly turn cloudy when haze-active proteins and polyphenols cuddle in the chilly beer. If you are OK with that, all is good. But if you want clear beer, you have a problem that requires us to roll back the timeline a bit.

An easy and effective solution is to add AN PEP when you pitch your yeast. In the U.S., White Labs sells a diluted version of Brewers Clarex® called Clarity Ferm to homebrewers. If you have access to this product, it’s the easiest path forward. If not, and you want clear beer, you are going to need to chill your beer after lagering. One option is to position your lagering vessel/keg in a bucket at the beginning of the lagering process. After 3-4 weeks, use ice, water, and some salt to make a water brine with a temperature around 28 °F (-2 °C). To maintain this cold temperature, you will need to add ice and salt several times per day. The good news is that cold stabilization only takes 1–2 days. But the bad news is that commercial brewers typically filter beer at this stage because chill haze particles are only slightly denser than beer and take a very long time to settle. And I’m guessing you don’t want to filter or mess around with silica gel or PVPP.

Another option is to use the ice and salt trick to get your beer very cold without buying a second refrigerator and fining your beer with something like Kieselsol or Biofine Clear. This process, although requiring cold temperatures, is much faster than traditional cold conditioning and much easier than filtration. You must add Kieselsol or Biofine Clear at least a few days prior to bottling because the sediment should be removed before consuming and the sediment is too fluffy to decant beer from the bottle. 

Response by Ashton Lewis.