Water is essential for binding the flour particles into a dough, and the water content is especially critical in pastries because there is so little. Pastry cooks say that as little as ½ teaspoon/3 ml variation in water in 1 cup/120 gm flour can make the difference between a crumbly texture and a tough one. Eggs are often used to provide richness and added cohesiveness to crumbly pastries, and of course also contribute water. Various dairy products, including milk, cream, sour cream, crème fraîche, and cream cheese may replace some or all of the water, and at the same time provide flavor and fat as well as sugars and proteins for the browning reactions. Salt is added mainly for flavor, though it does have a tightening effect on gluten.