Acetoin forms a solid dimer on standing, and is avalable as a mixture of the liquid monomer and solid dimer. The dimer is easily converted back to the (liquid) monomer by melting, or dissolving in water, ethanol, or propylene glycol. It oxidizes gradually to diacetyl on exposure to air. Acetoin is a very useful flavor ingredient, as it provides a characterizing butter flavor, and can contribute fatty, body, creamy, and buttery characters to many flavors. It can be found in a variety of foods like apples, blackcurrants, blackberry, cantaloupe, asparagus, wheat, broccoli, brussels sprouts, butter, yogurt, cheeses, chicken, pork, coffee, and many other foods.