Set yoghurt can be thickened even further and turned into Greekstyle yoghurt by straining it through a cloth.
The chilled yoghurt is a mixture of casein (milk protein), lactic acid (converted from lactose or milksugar), fat and water. The yoghurt looks and feels firm, because of the precipitated casein solids. These can no longer remain dissolved once fermentation turns the milk acid.
To make the yoghurt taste milder, we can drive off the lactic acid with the water by letting it drip out through a piece of cheesecloth.
What remains is a custardlike substance which tastes almost sweet .
Cheese cloth can be purchased in cookware shops. It is usually bleached. Cut off a length that will fit inside a sieve or collander or steamer insert, with a generous overlap to accommodate the yoghurt.
The cloth will need washing and sterilizing in boiling water prior to using.
Fitting the cloth in a steamer arrangement means you can catch the drippings easily.I must admit that as yet I am not sure about the nutritional value of the liquid. I have a feeling that this is where the B Vitamins hang out, in which case it would be a shame to discard it. Watch this space.
However, drinking almost a pint of this acid juice can be a little daunting . Besides, I have no information about the keeping qualities of this liquid.
The jar with the yoghurt can be placed upside down on the cloth and left in place, or the yoghurt can be scooped out straight onto the cloth.
Mine is usually so firm that I have to break the surface tension and stir it first, or else nothing will drip out.
I therefore prefer to take it out of the jar altogether.
Cover the pan with a lid, put in a cool place and forget about it for three or four hours.
By that time most of the liquid will have dripped out and you are left with a substance like stiffly whipped cream.
This is particularly effective when using full cream milk. In fact, true Greek yoghurt is made with cream added to the milk, to make it extra rich.