The other night I was making a batch of Nigella’s apple and almond spelt muffins from Kitchen. I pulled out the yoghurt and only then noticed it had developed a fine layer of black mould over it. Appetising. Halfway through the recipe, with some of the ingredients combined, I couldn’t just call it a day.
If you’re in this situation you could substitute buttermilk, of course, but I didn’t have any buttermilk either. Instead, I poured out the required volume of milk (the recipe calls for 60ml yoghurt, so I used 60ml milk) and added a teaspoon of vinegar to acidulate it, then let it stand a few minutes. You could use lemon juice as well, but will probably need a touch more than a teaspoon. The vinegar was just to adjust the acidity levels of the recipe to ensure an even rise.
The muffin mixture was a bit looser than usual, as milk is thinner than yoghurt, and the crumb wasn’t as tender. They took a couple of minutes longer to bake, and I have the feeling they staled a little faster. However, it was an excellent emergency measure!