The general consensus is that culturing milk to produce yogurt originated about 6000-7000 years ago in Central Asia and that it may have been introduced to Western Europe via Turkey . It may have been known in Ancient Greece as oxygala (oxy meaning sour or vinegar, gala meaning milk), or this may have been a yogurt-like drink, or possibly a cottage cheese or cream cheese [2-5]. In the description of oxygala in , Pliny the Elder says that “sour milk being added to the fresh milk which is wanted to curdle” which is how we make yogurt, by adding the starter culture to warm milk. Cottage cheese or paneer can be made by adding citric acid or vinegar to milk. It’s possible that oxygala referred to both of these dairy items (cultured milk and milk curdled with vinegar) or that somehow the term became confused as both preparations are being in alluded to in Pliny the Elder’s chapters 35 and 36. Many secondary sources claim oxygala was eaten sometimes sweetened with honey, but I cannot find a primary source to confirm this. Strained yogurt is known modernly in Greece as straggisto.
A modern recipe for making yogurt that could absolutely have been done in period is as follows*:
In a pot or crockpot: Pour half a gallon of milk (sheep, goat, or cow) into a pot. Heat the milk to 180F (use a thermometer) to denature the protein and kill off any existing bacteria. Allow it to cool to around 107F. Mix in half a cup of yogurt from a previous batch (or get half a cup of plain yogurt from the store) with the warmed milk until completely mixed. Add this back to the pot. Wrap the pot in a towel to hold at this temperature for 8-12 hours. The longer it cultures the stronger the flavor will be and the thicker it will get.
In an instant pot: Pour half a gallon of milk (sheep, goat, or cow) into a pot. Use the yogurt setting on temp high. When it beeps, remove the inner pot and allow to cool to 107F. I put it in the fridge to speed it up. Mix in half a cup of yogurt from a previous batch (or get half a cup of plain yogurt from the store) with the warmed milk until completely mixed. Add this back to the pot. Put the inner pot back in and use the yogurt setting with temp med with the time set for 8-12 hours. I like 12 hours. When it beeps, it’s done.
To get straggisto, place a mesh strainer over a bowl and line with fine cheesecloth and pour the yogurt in. I like to push the thickened yogurt away from the cheese cloth at intervals with a spatula to allow the thinner yogurt to strain. I leave it in the fridge while straining so that it sets up and strains simultaneously; when done out of the fridge, I find that more than the whey strains off and I lose some yogurt. Once done, store in jars however you like. Tip: my yogurt done this way comes out more mild than store bought yogurt. I particularly like homemade goat or sheep milk yogurt as it’s very pleasantly mild. I top my yogurt with honey and walnuts, or sometimes just fresh berries. If you put the honey on and then store, the yogurt will react with the honey and become watery. It’s still safe to eat and tastes fine, but it loses some of the nice texture.
*This recipe works for me every time, but don’t take my word for it. The internet has TONS of articles on homemade yogurt and also troubleshooting what went wrong.
 History of yogurt and current patterns of consumption.
 Oxygala – Wikipedia.
 Pliny the Elder, The Natural History, CHAP. 36.—OXYGALA: ONE REMEDY.
 Charlton T. Lewis, Charles Short, A Latin Dictionary, oxygăla.
 Pliny the Elder, The Natural History. CHAP. 35.—TWENTY-FIVE REMEDIES DERIVED FROM BUTTER.