Humans secrete two kinds of saliva, stimulated and unstimulated, no more alike than most siblings. The prettier child is stimulated saliva. It comes from the parotid glands, between cheek and ear. When a plate of spaghetti carbonara makes your mouth water, that’s stimulated saliva. It makes up 70 to 90 percent of the two to three pints of saliva each of us generates daily. Stimulated saliva looks, tastes and flows like water — it is, in fact, 99 percent water with some proteins and minerals. Each person’s saliva contains minerals in unique proportions.

The main digestive enzyme in stimulated saliva is amylase, which breaks starches down into simple sugars that the body can make use of. You can taste this happening when you chew bread. A sweet taste materializes as your saliva mixes with the starch. Add a few drops of saliva to a spoonful of custard, and within seconds it’s much more like water.

Allowing you to eat is the most obvious, but far from the only, favor granted by saliva. Vinegar, cola, citrus juice, wine — all are in the acid range of the pH scale: from around pH 2 to 3. Anything under pH 4 will dissolve calcium phosphate, a key component of tooth enamel.