Daisy;
The function of milk in pizza, or any other type of yeast leavened dough will depend largely upon the amount of milk used/added. At levels of less than 25% of the total flour weight fluid whole milk is just a more expensive form of water, however, when you get up to 5% or more using dry whole milk solids, you will begin to see added browning of the crust due to the lactose (milk sugar) in the dry whole milk, and when you get up to the 8 to 10% level you will get a flavor contribution in addition to the browning. The calcium content of the milk, when used at levels above 4% can act as a buffer to control acid development in the dough with long fermentation times. The use of fluid whole milk can carry some food safety risks with it if not kept refrigerated, plus it should be scalded prior to using it in a dough to prevent unwanted softening of the dough (this is why many cook books say to scald the milk before use). This is not necessary when using dry whole milk solids, but be aware that you should use “high heat, bakery grade dry whole milk solids” rather than plain dry milk solids that you might find at the local supermarket, or buy from some restaurant/school suppliers. One last thing, when you get up to that 5% level of dry whole milk you might also see some strengthening of the dough due to the calcium ion effect upon the wheat gluten forming proteins. When converting from liquid to dry milk you should use approximately 1.5-ounces dry whole milk solids to replace 1-pound (16-ounces) of fluid whole milk, then remember to add back 14.5-ounces of water (1.5 + 14.5 = 16-ounces). When making bread, there is a standard of identity for “milk bread” that standard calls for ALL of the liquid added to the dough to be fluid milk (no, you can’t add fluid milk and water and still call it milk bread), but you can add not less than 8.2% dry milk solids (based on the total flour weight) plus water to hydrate the dough and still call it milk bread.
Tom Lehmann/ The Dough Doctor