Homemade yogurtI suggest scaling the recipe to fit whatever thermos you have, mine holds about 900ml so I made a bit less than the recipe below. Most recipes suggest adding powdered milk to make the yogurt thicker, I didn't have any and it still worked but was a pouring yogurt consistency. I drained half my finished yogurt through muslin for a few hours and was left with beautifully thick yogurt, this is what greek yogurt is.
1 L milk (I used full cream but I have read that skim will work)
1/2 C natural yogurt with live cultures
1/4 C powdered milk (makes thicker yogurt)
3 T sugar (for sweetened yogurt)
vanilla bean or extract
thermos ~ 1 L capacity
strainer and muslin or new chux cloth
Fill the thermos with boiling water and leave to heat.
Heat the milk in the saucepan, stirring to prevent it scalding on the bottom, to 95C or until almost boiling, that is when bubbles are just appearing around the edges of the pan. Remove from heat and add the powdered milk, sugar and/or vanilla if using, stir to dissolve.
Cool until it reaches 43°C or when the milk is just cool enough for you to comfortably hold your finger in it for 10 seconds. Place the saucepan in a sink/bowl of cold water if you are in a hurry.
Add a slurp of warm milk to the yogurt in a bowl and mix until smooth. Return to the warm milk and combine.
Empty the water from the thermos and fill with the mixture. Seal and leave overnight. Some recipes I read said it may set in 3 hours, mine wasn't so I left it till the morning. The longer you leave it, the more tart it will become. Ours was only mildly tart after 12 hours.
Store in the fridge.
If you want thicker yogurt drain in a muslin lined strainer in the fridge.