Back in Scotland when I lived in houses with big cast iron range cookers in the kitchen, I used to make yoghurt all the time. It was so easy just to sit it in a water bath on the back of the stove. Since then, I’ve not been very successful at finding a way of keeping the yoghurt at the right temperature for the required time, short of buying an electric yoghurt maker which I really didn’t/don’t want to do.
But now I have. It was obvious really. I don’t know why I didn’t think of it before.
I don’t doubt electric yoghurt makers are useful pieces of equipment that many people swear by, but to me they just feel wrong. In the same way it feels wrong to use an electric bread machine. It’s not just the unnecessary use of electric power. Making bread, making yoghurt (and cheese) have a sense of the sacred about them. Something to be done always by hand in ritual connection with all the millions of people throughout the world for thousands of years who have daily prepared this most basic of all human sustenance. A direct line to a deep and fundamental ancestral simplicity. There is no way I could or would hand that pleasure over to a machine!
But how to make yoghurt in a yurt with no steady source of heat around the right temperature?
Thinking about how long a hot water bottle stays hot under a duvet, it all came together. So with a hot water bottle, a coolbox, some synthetic wool-like insulation material and a heat-seeking cat (who volunteers for the job every time – clearly the coolbox is not the best of insulators), we now have perfect yoghurt a litre at a time.
This is a technique for a beautiful thick mild yoghurt I learned from a conversation with Katherine Biss at the West Highland Dairy 20-odd years ago. Many yoghurt recipes call for a much longer time at a lower temperature, but this short sharp process works for me every time with cows milk and goats milk alike. The higher temperature favours different strains of bacteria which produce a firmer set and a milder flavour to the more tart and acidic taste produced by the bacteria that proliferate at lower temperatures. 4 hours is all they need.
Heat just shy of a litre of milk to boiling point then remove from heat, cover and allow to cool to around 40°C (or as hot as a hand can reasonably stand if you don’t have/can’t be bothered with a thermometer). While the milk cools, sterilise an airtight lidded 1 litre container (I use a Le Parfait/Kilner-type glass clip-top preserving jar) in boiling water. When the milk is cool enough, stir in the starter culture – a pot of plain natural live yoghurt or a couple of tablespoons of the last batch – with a whisk and pour the milk into the jar. Seal and keep at 40°C for 4 hours. Remove and cool straight away.
(A good quality live yoghurt containing cultures of Lactobacillus bulgaricus and Streptococcus thermophilus should theoretically be capable of perpetuating indefinitely under the right conditions, but freeze-dried yoghurt starters and other cultures tend not to last longer than 4-5 batches. Some are designed for single use only.)