There is no need for sterilization, the sugar will not allow bacteria to grow. After churning butter, liquid is produced. This is originally called buttermilk. A better process is to introduce buttermilk cultures to whole or skimmed milk, it is then homogenized and pasteurized. This is not real buttermilk, it is a product resembling buttermilk.
Natural buttermilk is dried and then sold to pancake companies to be used in pancake mixes.
The reason for this being that it will produce a better flavor than artificial buttermilk. Pasteurized and homogenized. Product thickens while bacteria multiply. Flavorings and stabilizers are added before the product is packaged. Do not count on the upper limit .