Fermentation

The most obvious difference between ales and lagers is the temperature at which fermentation is conducted. As you probably know by know, the key difference between ales and lagers is the type of yeast used for each style. Ale yeasts (Saccharomyces cerevisiae) are top-fermenting yeasts and tend to prefer temperatures between 65º F and 72º F. Lager yeasts (Saccharomyces uvarum), on the hand, are bottom-fermenting and ferment best somewhere between 40º F and 55º F, depending on the type of yeast. A big dilemma for many homebrewers is how to keep consistently cool temperatures throughout the fermentation process. The strain of yeast used and the temperature at which fermentation is conducted contribute greatly to the final lager. Off-flavors caused by erratic or inappropriate fermentation temperatures tend to be more pronounced in lagers than ales, so strict temperature control is an important issue for lager-brewing.

Some people can find a nice cool corner of their basement to ferment, but that may depend on the season. While lager-brewing was originally based on the seasons, this is not the 1840's and we're the beneficiaries of over 160 years of subsequent technological advancement. So take advantage of it - get a cheap refrigerator (used ones work fine) and convert it into your lagering fridge. A temperature regulator is a highly recommended investment to make sure you control the fermentation temperature as close as possible. If you don't lager all the time, with the right conversion kit, the fridge can double as a kegerator for dispensing draft beer. Or just find a nice cool corner in a basement somewhere and cross your fingers.

While a simple ale may only require a week or two of fermentation before being bottled, lager requires a minimum of 2 - 3 months before it's ready to drink. Primary fermentation should be a minimum of 2 weeks. A secondary fermentation is absolutely necessary for lagers and should be done for a minimum of 2 more weeks (4 would be preferred). The longer fermentation is necessary for lagers as fermentation is slower than the tumultuous ale fermentations you're more familiar with. Furthermore, a longer secondary fermentation greatly assists the lager in clearing.

Tip: Lager fermentations produce more sulfur than ale fermentations, so do not be surprised to get a "rotten egg" smell coming from your airlock. It's normal. Just allow the beer to ferment for an appropriate amount of time and all sulfur-producing compounds will be eaten by the yeast.