The mid-1980s saw increased usage of oak barrels for fermentation over stainless steel fermenting tanks. It took place when one of the wooden vats of fermenting porter burst. Fresh cane juice was now available for fermenting and distilling into rum. Chemically, biofuels are alcohols produced by fermenting raw materials from starch and sugars. This mainly involved salting, curing, curdling, drying, pickling, fermenting, and smoking. In addition to fermenting the beer, yeast influences the character and flavour. Galactose and fructose are shown to be two of the best fermenting sugars. These feed on the mother of vinegar and can occur in naturally fermenting vinegar. Ethanol is an alcohol produced from fermenting carbohydrates in plants. The ability to metabolize alcohol likely predates humanity with primates eating fermenting fruit. This wine was made by adding water to pomace and then fermenting it. They also used the pigment verdigris, made by soaking copper plates in fermenting wine. There is also a long-standing Scandinavian tradition of fermenting berries into wine. "Douchi" is made by fermenting and salting black soybeans. He simulated the traditional Chinese method of making Keemun by fermenting the tea in barrels.