Digestion (largely the glucose-insulin system) have been uncovered in recent years. Digestion is a complex process controlled by several factors. pH plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx and esophagus, pH is typically about 6.8, very weakly acidic. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment. The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two
Digestive biscuit packs sold annually. Digestives are also popular in food preparation for making into bases for cheesecakes and similar desserts. Chocolate digestive biscuits are also available, coated on the underside with milk, dark or white chocolate. Originally produced by McVitie's in 1925 in the UK as the Chocolate Homewheat Digestive, other varieties include the basic biscuit with chocolate shavings throughout (chocolate "chips" in the biscuit mix), or a layer of caramel, mint chocolate, orange-flavoured chocolate, or plain chocolate. American travel writer Bill Bryson described the chocolate digestive as "a British masterpiece". The McVitie's chocolate digestive is the most popular biscuit in