Calcium oxide

Calcium oxide (quicklime) is a highly reactive white powder produced by calcining limestone at high temperatures. When added to water or moist foods, it immediately reacts to form calcium hydroxide (slaked lime), generating heat. In food processing it is used for pH adjustment in alkaline treatments, in certain cereal processing applications, and historically in the preservation of certain traditional fermented and cured foods.

JECFA's ADI is "not specified," evaluated in 1965. Calcium oxide rapidly hydrates to calcium hydroxide on contact with moisture, so no calcium oxide as such persists in food — only calcium hydroxide and its neutralisation products (calcium salts). These provide bioavailable calcium. The food-safe use of calcium oxide is at concentrations that are fully converted during processing.

Calcium oxide is approved in the EU, US (GRAS), UK, and globally as a food processing agent. Its food applications are more limited than calcium hydroxide due to its greater reactivity. For consumers there are no safety concerns from its approved processing use. Like other calcium alkalising agents, it can contribute nutritionally beneficial calcium to processed foods.