2L fresh full fat milk (or semi, but it's not as tasty)
125ml fresh live yogurt
Equipment:
Four 500ml glass jars with lids
Esky big enough to fit the four jars
Large saucepan (at least 2L ) with lid
Cooking thermometer ranging from 0°C to 100°C
First, sterilise the jars and lids - put 3cm of water in the pan with the jars and lids and boil for 10 mins with the lid on. Allow to cool a little then remove the jars, pour out any water and put the lids on loosely.
Next, place the milk in the saucepan, stick the thermometer in and put the lid on. Place over a medium heat until the milk reaches 85°C - 90°C - do not let the milk boil, it will make a huge mess and also ruin the yogurt. With the lid still on, place the pan in the sink and fill with cold water to an inch below the top of the pan, and cool the milk to 50°C - 55°C .
When the milk has cooled, take 125ml of the milk, place in a bowl with 125ml of the yogurt and mix well. Pour the milk/yogurt mix back into the pan and mix well. When mixed, pour the mixture into the glass jars filling to the top, and put the lids on tightly. Place the jars in the Esky and pour in water at 55°C to an inch of the top of the jars. Put the thermometer in the Esky too, and leave for five hours. Once an hour check the temperature - if it is below 40°C remove a cup of the water and replace with boiling water, being careful to avoid pouring the boiling water directly over the jars. After five hours open a jar and check the consistency - if it has gelled then the yogurt is done. Place in the fridge and eat within two weeks.
If the yogurt has not gelled there are a number of things that might be wrong:
- The milk or yogurt wasn't fresh enough - buy them both that day, and get the packs with the longest expiry you can find
- The yogurt wasn't live - make sure it says on the pack that it contains Lactobacillus acidophilus
- The temperature varied too much - keep it between 40°C and 55°C , ideally between 45°C and 50°C