Yeasties and Oddities
Beyond the basics of malt and hops, artisanal brewers take advantage of countless other sources of flavor and aroma when they formulate their beers. Besides water, we are still missing one crucial beer ingredient: yeast. During fermentation, yeast not only turns maltose (sugar) into alcohol, it can provide a full range of flavors. While American strains are usually more neutral, English yeast strains provide fruity esters, German hefeweizen yeast can add banana and clove flavors, and Belgian strains can offer phenolic notes, and wild yeasts can add anything between lemons and horse blankets.
The variety of yeasts is vast, but what does this mean in terms of keeping our beer fresh? The yeast profile of a beer should be regarded similarly to malt flavors of a beer. The overall complexity of a beer can generally be correlated successfully to the shelf life of a beer (with notable exceptions—never forget the hops). Flavors and aromas created by the yeast will fade over time, but the more there is the longer it will take to fade away. Yeast strains that add intense flavors to beers, such as Belgian ale yeast strains, add to the shelf life of beer. Neutral yeast strains, such as American ale yeast, add very little, and so the beer is only as vulnerable to degradation as the sum of its other ingredients.
One oddity when it comes to the age of beer is sour beer, or wild ales and lambics. In these beers, a spectrum of wild yeasts and bacterias help to ferment them, resulting in pungent flavors, mostly sour and funk. Many regard these sour beers as the best beers to age, even though they may have little alcohol and very few hops. While your experiences may vary, these can normally easily be stored for at least a couple of years without any negative impact on the beer.