Making yoghurt (yogurt)

I noticed in the delicatessen the other day that quark is now selling for $19.50 a kilo. Naturally I didn't buy any as I make my own but nevertheless, I was shocked by the price. Of course, any food linked to cattle - beef, milk and cheese - has increased a lot recently. I heard on the news the other day that food prices have doubled in the past couple of years. The price of the quark drove that