1 Gallon of yogurt/kefir cultured and then cooled completely
1.25 c sugar
1/4 c vanilla flavoring
Pour out some of the yogurt into a previous batch or a glass or bowl to make room for the flavoring (usually about 1 cup or just down from top of handle shoulder).
Add sugar and vanilla flavoring. Replace cap. Shake to distribute the flavoring and break up the protein clumps. Often times I will hold upside down and shake to see if any sugar or vanilla has settled at the bottom.
Shake before each use to mix in the sweetener and to mix in any separation (e.g. yellow liquid whey that has separated as settled).