Brewing much studied, the preservative nature of the soft resins is not yet fully understood, though it has been observed that unless stored at a cool temperature, the preservative nature will decrease. Brewing is the sole major commercial use of hops. Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolises the sugars extracted from grains, which produces alcohol and carbon dioxide, and thereby turns wort into beer. In addition to fermenting the beer, yeast influences the character and flavour. The dominant types of yeast used to make beer are "Saccharomyces cerevisiae", known as ale yeast, and "Saccharomyces
Isopropyl alcohol used as both solvent and hydride source in the Meerwein-Ponndorf-Verley reduction and other transfer hydrogenation reactions. Isopropyl alcohol may be converted to 2-bromopropane using phosphorus tribromide, or dehydrated to propene by heating with sulfuric acid. Like most alcohols, isopropyl alcohol reacts with active metals such as potassium to form alkoxides that can be called "isopropoxides". The reaction with aluminium (initiated by a trace of mercury) is used to prepare the catalyst aluminium isopropoxide. In 1920, Standard Oil first produced isopropyl alcohol by hydrating propene. Its major use at the time was not rubbing alcohol but for oxidation to acetone, whose