Beer style beer differently. Since sugars are converted to alcohol during the process of fermentation, gravity can be used to estimate the final alcohol. In beer brewing, a distinction is made between the "original gravity", the gravity of the wort before fermentation has begun, and the "final gravity" of the product when fermentation has completed. Since the concentration of sugars is directly proportional to the gravity, the original gravity gives a brewer an idea of the potential alcoholic strength of the final product. After fermentation, the differences between the final and original gravities indicates the amount of sugar converted into alcohol, allowing
Brewing of time; brewing yeast strains act slower, but tend to tolerate higher alcohol concentrations (normally 12–15% abv is the maximum, though under special treatment some ethanol-tolerant strains can be coaxed up to around 20%). Modern quantitative genomics has revealed the complexity of "Saccharomyces" species to the extent that yeasts involved in beer and wine production commonly involve hybrids of so-called pure species. As such, the yeasts involved in what has been typically called top-cropping or top-fermenting ale may be both "Saccharomyces cerevisiae" and complex hybrids of "Saccharomyces cerevisiae" and "Saccharomyces kudriavzevii". Three notable ales, Chimay, Orval and Westmalle, are fermented