The cuisine of ancient Egypt covers a span of over three thousand years, but still retained many consistent traits until well into Greco-Roman times. The staples of both poor and wealthy Egyptians were bread and beer, often accompanied by green-shooted onions, other vegetables, and to a lesser extent meat, game and fish. Food could be prepared by stewing, baking, boiling, grilling, frying, or roasting. Spices and herbs were added for flavor, though the former were expensive imports and therefore confined to the tables of the wealthy. Food such as meats was mostly preserved by salting, and dates and raisins could be dried for long-term storage. The staples bread and beer were usually prepared in the same locations, as the yeast used for bread was also used for brewing. Beer was a primary source of nutrition, and consumed daily. Beer was such an important part of the Egyptian diet that it was even used as currency. Unlike European beer, it was cloudy with plenty of solids and highly nutritious, reminiscent of gruel. It was an important source of protein, minerals and vitamins. Bas-relief from unidentified temple.