Making yoghurt at home is easier than you think, but can also prove a little fickle. It is simply pure milk heated and inoculated with a particular bacteria, that then has the full freedom of the medium to convert the lactose into lactose acid. However, while the natural bacteria in milk is good for cheese making, the same cannot be said for yoghurt. Therefore, the milk needs to be heated to a high temperature to knock out all the bacteria before you then add the good bacteria – either from your previous batch of yoghurt or a good-quality commercial live yoghurt (check the label to ensure it only contains milk solids and live yoghurt cultures – no flavours, emulsifiers or thickeners).
- 2 litres non-homogenised milk
- 3 tbsp live natural yoghurt
Oven temperatures are for conventional; if using fan-forced (convection), reduce the temperature by 20˚C. | We use Australian tablespoons and cups: 1 teaspoon equals 5 ml; 1 tablespoon equals 20 ml; 1 cup equals 250 ml. | All herbs are fresh (unless specified) and cups are lightly packed. | All vegetables are medium size and peeled, unless specified. | All eggs are 55-60 g, unless specified.
Incubating time 12 hours
This is required to destroy any spoilage bacteria, thus allowing the desirable bacteria no competition to produce enough lactic acid to preserve the yoghurt. It also denatures the proteins a little, giving the yoghurt more viscosity.
Firstly, heat the milk in a sterile pan to 92°C – you can use a double boiler or put it straight on the heat (be very careful not to burn the milk as this will taint the product – keep stirring!). You will need to use a thermometer to check this temperature and keep stirring to ensure an even temperature throughout. Once the 92°C is attained, remove the pan from the heat.
Reduce heat quickly from 92°C to 35–40°C. Place the pan in a cold-water bath – use a double boiler system and replace the cold water, or put the pan straight into a sink if deep enough. Check the temperature frequently.
Adding the starter
Once the milk reaches 38°C, add the yoghurt and stir. Pour the milk into sterilised jars and fill right to the top, leaving no gap.
Never add the starter if the milk is higher than 45°C.
Afterwards, your own yoghurt can be used as the "mother" to make the next batch. However, over a few batches, the nature of the bacterial content may change slightly and, with it, the texture and flavour of the yoghurt may begin to change. If this is the case, start again with commercial yoghurt.
It is very important to get this right – if the temperature is too warm, then one bacteria will grow faster than the others and this will result in imbalanced flavour and texture. In Australia, most commercial yoghurts are incubated at 42–43°C for 4–6 hours (the longer the incubation the stronger the yoghurt), while European yoghurts are incubated for 12–16 hours at 33–35°C.
Keep the sealed jars in a warm place for 12–18 hours. An easy way of doing this is to place the jars in a small eski, with water surrounding the jars at the correct temperature. You can check every few hours and adjust the water temperature as required by replacing with warmer water. During the incubation, the bacteria will convert the lactose into lactic acid and the pH will decrease to the point where coagulation occurs.
After coagulation occurs, do not place the yoghurt in the fridge for at least 1 hour – it is this time after coagulation has occurred that will determine the flavour intensity of the yoghurt; the longer it is left, the stronger the flavour.
Keep in a tightly sealed jar and use within a week of making it.
• If adding fresh fruit to the yoghurt, the enzymes in the fruit will break down the yoghurt and the result will be watery. Add preserved fruit or jam or add fresh fruit when serving.