Home brewing is a richly rewarding experience. There is nothing quite like enjoying a cold bottle of your own homemade lager. Most home-brewed beers have an alcohol content between 4 and 5 per cent by volume. The secret to brewing a beer with a higher content (roughly 7 to 9% alcohol) is not necessarily to add more priming sugar or corn syrup after the first fermentation. A more effective method is to use a higher gravity malt base and a more attenuative yeast. This method will work for any barley-based beer, ale or lager.
Purchase a barley malt base that will increase gravity. Gravity is a term of art in brewing referring to the density of the malt in contrast to the amount of water used. Richer grains provide more sugars that will be converted to alcohol during the fermentation process. Malt extracts tend to have a higher density than whole grain or speciality grain malts, which will lead to a higher original specific gravity. Make sure the malt base is one that can be used in your recipe. There is no use brewing a stronger beer if you have to sacrifice flavour just to reach a higher alcohol content.
Select a highly attenuative yeast. Attenuation refers to the degree to which the yeast converts sugars from your barley malt into alcohol and carbon dioxide. The attenuation of the yeast directly correlates to the final alcohol content of your super strength beer. Make sure that the yeast pairs well with the recipe you use. Again, don't sacrifice balance and flavour just to reach a higher alcohol content. For example, if you decide to brew a stout or porter, use a yeast like White Labs Dry English Ale Yeast.
Increase the proportion of malt to water. The higher your ratio of malt to water, the higher the specific gravity of the wort you produce. Depending on the recipe, increase the amount of malt you boil in the mash tun by approximately 50 per cent. This will yield a denser wort with more sugars available for fermentation. Measure the specific gravity using your hydrometer. A gravity in the ballpark of 1.07 or 1.08 is optimal.
Add the yeast. After boiling the wort in the mash tun and adding hops for seasoning, add yeast and siphon the brew into the keg, growler or other container in which it will be stored throughout the fermentation process. Store at the temperature required by the recipe in a cool, dark location. Store top-fermenting lagers at around 65 degrees F / 18.3 degrees C and bottom-fermenting lagers at around 50 degrees F / 10 degrees C. Ensure that the brew is not exposed to any light or oxygen that would spoil the batch.
Increase the time for fermentation. You have given your yeast a greater task by increasing the amount of sugar it must respirate. A beer that ordinarily takes a month to ferment may take twice as long, depending on the recipe. The final gravity of the beer should be around 1.01 or 1.02.
You may want to oxygenate the brew before, during and after yeast fermentation to achieve the desired final gravity. If you are using a whole grain recipe instead of an extract, take care to sufficiently mash the barley to allow the sugars to mix properly with the water before fermentation.
Brewing stronger beer is a delicate process. If your original specific gravity is too high, you may wind up with a "stuck" fermentation and a spoiled batch of beer. Check the laws of your state to see what restrictions exist on home brewing in general and brewing high strength beers in particular.