How do I make lager beers? How is it different from making ales?

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Most homebrewers start off making ales because room-temperature fermentations are relatively easy to do. However, once they master the art of brewing ales, they yearn for a greater challenge. How about making a lager?

For most brewers, the big jump comes when they get a lagering refrigerator. Unless you want to make a California common or a Boston lager, there is pretty much no way around it. This acts as quite an impediment for the casual brewer. Once you make the jump, however, you will discover that there are other things you can do with the fridge. Like keeping your ales cold while you brew your lager.
Much of the difference between ales and lagers results from tradition and regional variations. When artificial refrigeration became widespread in the mid 1800's, European brewers were quick to jump on it. With the more refined beer flavors available, they insisted on more refined ingredients. Hence, we find the advent of Pilsner malt and a bunch of lager yeasts.

In past years, pilsner malts were considerably different from ale malts. In particular, they were less modified. Hence, mashing techniques required revision. Fortunately, modern malting techniques have pretty much obviated these necessities. Today, the main differences are a more refined flavor and paler color.

The differences in yeast are more significant. Lager yeasts are have been bred to produce a light body with delicate flavors. As a result, any flaws in brewing technique will become readily apparent. Phenolic odors, diacetyl and esters are considered off-flavors for lagers, though they can be tolerated in ales to various extents.

To make lagers, the first step is to choose a variety of interest. I recommend one of the more full-flavored varieties. If you like pale, go with a Bohemian Pilsner. For darker tastes, Bocks are good. Extract brewers will find the darker lagers easier to master, since few pale malts are light enough in color. One exception is if you add rice solids to the recipe.
The grain profile should start with Pilsner malt. Then a trace of light crystal or cara-pils for Pilsner. For Bock, add a bunch of Munich or Vienna malt. Avoid dark crystal malts.
Clarity is important for lagers, so use a protein rest when you start your mash. Later, during the boil, use Irish moss or other fining agents. Mash-in at 120°F and hold it for 20 to 30 minutes. Then step up to the starch conversion temperature. Decoctions add maltiness, though they are not required.

Since most lagers are European, the noble hops are traditional. Check the bittering level for your style, and remember that over-the-top flavor and finishing hops don't fit your style.
Control of fermentation conditions is the biggest factor to the success of your lager. Lager yeasts need the cool temperatures to avoid off flavors. Esters and phenolics are accentuated when the temperature is high. However, you don't want to go too cold, or stuck fermentations can result. In addition, the yeast won't be able to consume diacetyl. Here is the profile that works for me.
The first step is to make a starter. Most of you do this anyway, so this is no big deal. You can make your starter at room temperature, as long as it on the cool side. Pitch your wort at room temperature too. Then, put it in your lager fridge and set it to about 58°F. It should kick off within 24 hours. As soon as it does (but not before), drop the temperature to 50°F. Fermentation will take about a week, but don't worry if it takes two. Rack once the beer starts to settle, and give it another 2 weeks. By then, it should be ready for bottling or kegging.

If you bottle-condition your lager, remember that it holds more CO2 than ales. Hence, you need to cut back on priming sugar. If you usually use ¾ per 5 gallons, cut back to just over ½ cup.
At this point comes one of the great tricks of lager brewing: the diacetyl rest. Keep the bottles or kegs at room temperature for the first 2 to 3 days. This allows the yeast to have a surge of activity that will consume the lingering traces of diacetyl. Then, put them in the lagering fridge, staring at room temperature. Ramp the temperature down by 2 degrees per day. For Pilsner, go down to 34°F. For darker styles, 42°F should be sufficient.

Now come the hard part. Waiting. Is it ready yet? Nope. Give it at least a month. How about now? Yeah, pop one open!
You should note that your beer has excellent clarity. In the aroma you may notice a light corn-like aroma. This is dimethylsulfide (DMS), an expected part of most lager styles, at least as long as it blends with the malt. You should note no ester or diacetyl. The flavor should be crisp and fairly dry. It should also be unusually clean. Your overall impression should be, "Wow, why don't the commercial breweries make beer like this?"