What practice is known to destroy 90 percent of BST found in milk?

Pasteurization is a heat treatment process that effectively destroys harmful bacteria and extends the shelf life of milk. Specifically, it is known to reduce the levels of Bovine Somatotropin (BST), a growth hormone that can be present in milk, by as much as 90 percent. This significant reduction occurs as the milk is heated to a specific temperature for a set period, during which the BST is denatured and rendered inactive.

While homogenization is a mechanical process that breaks down fat globules to create a uniform texture in milk, it does not affect BST levels. Fermentation involves the use of bacteria to convert lactose into lactic acid, which can help in the production of dairy products like yogurt, but it doesn't specifically target BST. Skimming is the process of removing cream from milk, primarily affecting fat content rather than hormone levels. Thus, pasteurization stands out as the method specifically designed to reduce BST levels effectively in milk.