Yoghurt can be made from the milk of various animals, including cow, goat and sheep. Cream, whole, low-fat, skim, nonfat, or re-hydrated dry milk may be used.
Milk solids may be added to increase the nonfat solid content. This gives a firmer set to the yoghurt. Non-fat dry milk powder works well.
Starter cultures: Streptococcus thermophilus and Lactobacillus bulgaricus are the cultures most often used to make yogurt. Dry cultures may be purchased in health food stores or on the Internet. Or, plain yoghurt with live and active cultures may be purchased from a local store. Check the label to see that the product contains live cultures. To maintain a culture, save a small portion of yoghurt (1 cup for a 3 litre batch, ¼ cup for a 1-quart batch) to use as a starter culture for the next batch. Place this in a clean, airtight container and store in the refrigerator, sealed, until you are ready to use it.
Optional additions may be sweeteners such as sugar, honey or artificial sweeteners; fruit or other flavorings; gelatin for thickening.