Different equipment is used when preparing an angel food cake at home or in a small bakery as opposed to a large scale production. Many recipes found in cookbooks advise bakers to whip the egg whites in a copper bowl. The theory behind this is that the whisk incorporates copper particles or ovotransferrin, which is attached to copper particles, into the egg whites, improving the flexibility and stability of the foam. Some research has found that the copper significantly increases the dilatational elasticity, which is the elasticity of the protein cell wall at the interface of air/water.