Making yoghurt in a Thermos

Ever made the mistake of Googling yoghurt making?

I have traditionally used the technique laid out in The Encyclopedia of Country Living and not questioned it. It has always worked, I haven't had a batch go bad - and I haven't poisoned anyone yet. But before I put this down here for others to follow, I thought I would check that the procedure was safe and up to date. And so the fun began.

Yoghurt making begins with warming your milk. Some internet authorities state that you should heat your milk to sterilize it before allowing it to cool to optimum yoghurt culturing temperature. Some say using shop bought pasteurized milk means you can skip the sterilization, but should certainly sterilize fresh raw milk because of all the pus and TB and stuff. Some say that using fresh raw milk is safe but you wouldn't want to use shop bought milk without sterilizing it, because of all the pus and TB and stuff. Heating the milk apparently has another advantage apart from ensuring your milk is safe, in that it breaks down the milk proteins, resulting in a thicker yoghurt. But to what temperature? The ever reliable interwebs give ranges from the aforementioned 0 degrees C for 0 minutes, through 65 degrees C for 1 - 30 minutes, right up to 85 degrees C for 1 - 30 minutes. Helpful, no?

I think that this method from the US National Center for Home Food Preservation  is possibly the most thorough and well explained, definitely worth a read. My method is not that different, apart from I merely bring the milk to an almost simmer, I don't hold it there. I also make mine in a regular Thermos flask, which is the simplest way to keep the temperature constant with no need to expend extra energy (and therefore money) on the process. In the absence of a thermos, I have wrapped the saucepan in heavy blankets overnight and placed it in a warm room. Methods involving running a low oven or heat pad for hours on end seem unnecessarily wasteful.

I find a thermometer essential to work out when it is safe to add the live culture. Too hot or too cold and it will not work, a thermometer takes away the guess work and has plenty of other applications in the kitchen that it is worth spending a few pennies on one. I don't follow the recommendation to add powdered milk, because a thinner yoghurt suits us. We use full fat, but you can use any milk, from reconstituted powdered skimmed milk to fresh blue-top with a dollop of cream added - the fattier the starter, the naturally thicker the end product.

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Yoghurt (makes 1 litre)

1 litre full fat milk

2 tbsp live yoghurt

Ensure all utensils are clean and sterile. Scalding them with hot water should suffice. 

In a large saucepan and stirring constantly, slowly heat the milk to just below boiling point - it will be steaming and starting to foam slightly. 

Remove from the heat and place the pan in a bowl of cold water to cool quickly.

When cooled to around 43-45 degrees C, stir in the live yoghurt, pour into the Thermos and leave for a minimum of six hours. A maximum of 12 allows for a better set.

Transfer to a lidded jar and store in the fridge for up to 5 days. 

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I love my Thermos very much, it is a regular 1 litre capacity drinks flask. A wide necked one would be useful, but the yoghurt is quite pourable, you just need a bottle brush to clean it effectively.