or fine grater can be used to grind small amounts; a coffee grinder is useful for larger amounts. A frequently used spice such as black pepper may merit storage in its own hand grinder or mill. The flavor of a spice is derived in part from compounds (volatile oils) that oxidize or evaporate when exposed to air. Grinding a spice greatly increases its surface area and so increases the rates of oxidation and evaporation. Thus, the flavor is maximized by storing a spice whole and grinding when needed. The shelf life of a whole dry spice is roughly two years; of a ground spice roughly six months. The "flavor life" of a ground spice can be much shorter. Ground spices are better stored away from light. Some flavor elements in spices are soluble in water; many are soluble in oil or fat. As a general rule, the flavors from a spice take time to infuse into the food so spices are added early in preparation. This contrasts to herbs which are usually added late in preparation. Salmonella contamination A study by the Food and Drug Administration of shipments of spices to the United States during fiscal years 2007–2009 showed about 7% of the shipments were contaminated by Salmonella bacteria, some of it antibiotic-resistant. As most spices are cooked before being served salmonella contamination often has no effect, but some spices, particularly pepper, are often eaten raw and present at table for convenient use. Shipments from Mexico and India, a major producer, were the most frequently contaminated. Food irradiation is said to minimise this risk. Health research Spices have been claimed to have health effects during both ancient and current times; for example, in 2017, the Washington Post said spices put "a natural pharmacy in your kitchen". The supposed health benefits include antioxidant and anti-inflammatory effects, and benefits towards certain diseases. A 2019 systematic review looked at studies of 25 spices and concluded that there is not enough evidence yet to support these supposed benefits, and that "further work is needed". The review noted that many studies were conducted by administering capsule or "artificial" forms of the spices, but spices are not normally consumed in this manner, and are normally consumed along other foods. Spices may reduce the need for salt as a flavoring agent in dishes, which has cardiovascular benefits. Production Standardization The International Organization for Standardization addresses spices and