The louche effect is the name given when water is added to absinthe that turns the liquid white. The science behind it is quite normal and tends to happen when adding essential oils to water. Effectively, what happens is that the water is reacting with a hydrophobic chemical in the reaction. This effect was first described by Wilhelm Ostwald in 1896 and is known as the Ostwald Ripening effect. Absinthe fans call it the louche. The Osatwalk Ripening effect occurs when an added ingredient creates a reaction that no longer puts the initial compound in equilibrium either due to the PH level, temperature, or common ions changing (the ability for the alcohol to bond with the oil). As alcohol and water share relatively the same PH level, the biggest changes in the louche effect occur from temperature. Colder absinthe will cloud up faster than warm absinthe. As more cold water is added, the louche will become increasingly clear.