How yoghurt is made: The basic principles.
Quite simply, when our yoghurt cultures are added to milk, the cultures start to eat the lactose or any other available sugar. This happens best between 37° and 43° C.
We target 40° C in our instructions to allow for thermometer error etc., as the culture will start dying at 45°C.
10 to 12 hours at the desired temperature should make a beautiful yoghurt. The longer the yoghurt is kept in the ideal temperature range for culture growth, the more lactose, which is a dairy sugar, or other sugars available, get eaten. As more sugar is eaten, more acid is produced and the tangier the yoghurt becomes. Fermentation times up to 24 hours are becoming more popular too.
Please be aware that electric yoghurt makers may creep up in temperature with extended inoculation times, and sometimes become hot enough to kill the culture. This is seen by some as a benefit, as this will extend the shelf life of the yoghurt in your fridge. Thermos style yoghurt makers may need their heat reservoir water replaced to keep the yoghurt temperature in the correct range.
The yoghurt thickens due to the proteins bonding together. This happens with both dairy and soy milk, but not with coconut cream, for example, where a thickening agent is needed.
Stirring the dairy or soy yoghurt will break some of the bonds and should be avoided until serving. Coconut yoghurt and other yoghurts that use a thickening agent can be stirred.
How yoghurt is made: The basic methodology.
Electric yoghurt makers should not be used to heat the milk to the correct temperature as the heating process will be slow, which is highly likely to lead to unbalanced culture growth and the possibility of an undesirable texture. We recommend preheating the milk so that it is in the correct temperature range of 37 to 43 °C when the culture is added and mixed in.
Some electric yoghurt makers will slowly creep up in temperature over time and reach temperatures that will kill the culture, this will extend the life of the yoghurt in your fridge, but any probiotic cultures will be killed too.
GLA's Yoghurt Maker has been designed to hold the temperature in the correct range indefinitely and is ideal for extended fermentation times.
Thermos-style yoghurt makers will help maintain the temperature of your milk, so the milk should be at 40 to 43 °C when placed in the yoghurt maker. Any hot water placed in your system to act as a heat reservoir should not touch the internal yoghurt container, as this can cause the milk to heat rapidly, and excessively.
In the cold months, or if wishing extended inoculation times, you may need to change the hot water used as the heat reservoir, and keep the yoghurt maker well wrapped and in a warm place.
If using the EasiYo system, do not fill the external container so high with boiling water as to have it come into direct contact with the internal yoghurt container, as this will cause the temperature to rise too high, scalding and killing the culture. Just fill it to just below the hole in the baffle (red shelf). This will give you the benefit of a heat reservoir, without risking killing the culture. Monitor the temperature if concerned and replace the boiling water every 8 hours, or as required to maintain the temperature between 37º to 43ºC.
As with making any fermented milk products, cleanliness is vital in yoghurt making. Make sure that you thoroughly clean and sterilise all your utensils before using them. By heating milk to 40° C and then keeping it at that temperature you are deliberately creating the perfect environment to grow bacteria. Just be sure that you are only growing the bacteria (starter culture) that you have introduced, and not some other bacteria, mould or yeast that blew in on the wind.
Shelf Life of Cultures:
When stored correctly freeze-dried lactic cultures are typically viable long after any date on the pack.