Modern observers may forget that in earlier times, the purpose of fermentation was not simply to produce alcohol, but to produce a stable food product that would not spoil. Our ancestors could not store grapes from season to season, but they could store the fermented juice. Most people are aware of the bacteriostatic properties of alcohol and that a beverage’s susceptibility to spoilage decreases with increasing alcohol content. (Hey, who worries about 80-proof Scotch going bad?)
Yet another important factor is acidity, since many spoilage microbes cannot tolerate an acidic environment. Because organic acids are another byproduct of fermentation, acidity also protects fermented beverages.
Most beers have a pH level between 4.0 and 4.5. Because grape juice naturally contains acid, wine has a lower pH of about 3.5. (The lower the pH value, the more acidic the solution. Distilled water has a neutral pH of 7. Values above 7.0 are alkaline, and those below 7.0 are acidic.)
Compared to the average beer, wine is more acidic, contains more alcohol, and has a longer shelf life. The combination of wort boiling, alcohol, and acidic pH stabilizes beer, but because beer has only moderate levels of alcohol and acidity, hops became the preferred flavoring. Bitter acids in hops not only balance the sweetness of the malt, but they also inhibit the growth of spoilage bacteria. Because no human pathogens can survive in beer even though it is relatively low in alcohol, beer has provided humankind with a safe source of drinking water throughout history.
While pathogens do not survive in beer, beer spoilage organisms can ruin the flavor. For this reason, many nationally distributed beers are heat-pasteurized. While pasteurization provides biological stabilization, the heat can accelerate staling oxidation. Many locally distributed beers are not pasteurized because they are bought and enjoyed shortly after packaging. However, Coors is an example of a nationally distributed beer that is unpasteurized, so it must be shipped cold to prevent spoiling. Keg beer is also shipped cold and typically consumed shortly after packaging, so it’s not pasteurized, either. Sterile filtration is an alternative for biologically stabilizing beer without heat, but that tight filtration can also filter out protein and hop constituents that would otherwise add body, head retention, and flavor.
Exogenous sulfites protect the grape must and wine from oxidation and microbial contamination. While normal-strength beers immediately undergo flavor deterioration after packaging due to even the smallest intrusion of oxygen, some wines (especially tannic red wines) mellow and improve with age. Even storage in the bottle can soften and improve the flavor of bold red wines, principally through the slow oxidation of harsh tannins and the release of aromatic compounds bound to these tannins (i.e., bouquet). For this reason, it is desirable to allow some young, harshly tannic red wines to “breathe” before serving by decanting them from the bottle. Decanting mixes air with the wine, which accelerates the oxidation and mellowing of the tannins. However, prolonged exposure to air will eventually ruin the wine and turn it into vinegar. Tannins also have a preservative effect, allowing tannic wines like Bordeaux to benefit from many years of aging.
Aging strong barley wines can have the same mellowing effect on the harsh phenolic flavors derived from the grain husks of roasted malts. Aging also adds complexity through the production of sherry-like qualities from the oxidation of alcohols.
While brewers promote “born-on dates” to denote freshness and wineries date their vintages to indicate the benefits of aging, the stability of the raw materials that go into wine and beer have properties that are diametrically opposed. Grapes are inherently unstable and must be processed soon after harvest, before they brown or rot. Because grapes are unstable, wine must be produced to store from one growing season to the next. Drying malt renders it stable and capable of maintaining its high quality from one growing season to the next. While beer is more susceptible to flavor deterioration over time, fresh supplies can be brewed as needed over the course of a year.