Chapter 10 - What is Different for Brewing Lager Beer?
10.5 When to Lager
It takes experience for a brewer to know when primary fermentation is winding down and the beer is ready to be transferred. If you insist on brewing a lager for your very first beer, you are going to be flying blind. You can play it safe by waiting several weeks for the primary phase to completely finish (no more bubbling) and rack then, but you will have missed your opportunity for a diacetyl rest. As discussed in the previous chapter, you should rack to a secondary when the krausen has started to fall back in. The bubbling in the airlock will have slowed dramatically to 1 or 4 bubbles per minute, and a hydrometer reading should indicate that the beer is 3/4 of the way to the terminal gravity. Knowing when to rack takes experience, it's as simple as that.
I like to ferment and lager in glass carboys because the glass allows me to see the activity in the beer. During primary fermentation, there are clumps of yeast and trub rising and falling in the beer and it's bubbling like crazy- it literally looks like there is someone stirring it with a stick. When you see that kind of activity slow down, and things start settling towards the bottom, you know the primary phase is over and it's safe to rack.
The lagering temperature and duration are affected by both the primary fermentation temperature and the yeast strain. These are the four primary factors that determine the final character of the beer. Some general guidelines for fermentation times and temperatures are listed below:
- Check the yeast package information for recommended fermentation temperature(s).
- The temperature difference between the primary phase and the lager phase should be roughly 10°F.
- Nominal lagering times are 3 - 4 weeks at 45°F, 5 - 6 weeks at 40°F, or 7 - 8 weeks at 35°F.
- Stronger beers need to be lagered longer.
- Nothing is absolute. Brewing is both a science and an art.
A common question is, "If the beer will lager faster at higher temperatures, why would anyone lager at the low temperature?" Two reasons: first, in the days before refrigeration when lager beers were developed, icehouses were the common storage method - it's tradition. Second, the colder lagering temperatures seem to produce a smoother beer than warmer temperatures. This would seem to be due to the additional precipitation and settling of extraneous proteins (like chill haze) and tannins that occur at lower temperatures.