Ask Peter: Buttermilk
I've been using buttermilk instead of plain yoghurt in cooking (especially cakes, scones, etc) and it seems to work well. Is there a major difference between the two or are they always interchangeable?
Thanks, Lee Higgins
Years ago when we opened The Sugar Club in Wellington, I was using a recipe for muffins that required buttermilk. At the time I had no idea what it was, asked a few people and decided to make it myself. I whipped cream until it curdled then drained the curds off and used the milky part, the whey, in my muffins. They weren’t that great and I figured it was simply a bad recipe.
Later, I was talking to a friend who said I should sour my milk by adding vinegar, as that’s how you make buttermilk. I tried that, mixing 500ml whole-fat milk slowly into 2 Tbsp of white vinegar and leaving it at room temperature for 30 minutes. The muffins were more successful and, since that day, that’s what I do to make my own if I can’t find any.
More recently I’ve read a recipe that requires you to sit raw milk at room temperature for a few days until it forms a skin/crust on top. You then add more milk until it crusts, then do it one more time. The process takes around four days, depending on the quality of milk and the room temperature, but at the end of it you have a luscious, sour buttermilk. I’ve also read a recipe that requires you to add active buttermilk culture (and just how easy is that to find?) to milk and let it thicken at room temperature over a 24-hour period.
The latter two processes work along the lines of adding bacteria, lactobacillus, to the milk and, in the same way that yoghurt works, the bacteria convert the lactose in the milk into lactic acid, which gives it a slightly acidic, sour taste. So there are many ways to get just one ingredient. It’s not surprising that people get confused. I’ve only ever had buttermilk made from cow's milk, whereas yoghurt can be made from any milk, camel through to ewe.
To make yoghurt it’s a very similar process but generally it starts with the milk being heated to a temperature that kills off all bacteria present. Then the milk is cooled. Bacteria (similar to those used in buttermilk) are then added and as they increase in numbers, they begin to thicken the milk, also turning the lactose into lactic acid, which in turn gives the yoghurt the lovely sour taste we like. When I was at high school I used to make my own yoghurt by heating milk to body temperature then leaving it to cool for 20 minutes. I’d then add a few tablespoons of natural yoghurt to the cooled milk and place it in a covered jar in the hot water cupboard.
The next day I’d have yoghurt. To make the next batch I’d just add my own yoghurt to the jar of cooled milk and the bought variety became redundant. My yoghurt was never as thick as Greek-style yoghurt, but it was only in later years that I discovered milk powder is generally added to this style of yoghurt to thicken it to that luscious texture we enjoy.
As to why we use buttermilk in the first place, it’s rather like my recent article on baking powder vs. baking soda. Apart from the fact that the flavour of buttermilk is completely different to that of milk, it is also more acidic, as the lactose has been converted into lactic acid. The minute you mix buttermilk (or diluted yoghurt) with baking powder or baking soda, the chemical reaction causes the latter two powders to produce carbon dioxide bubbles. If these are in a batter (like my muffins) then, as heat is applied and the flour and eggs begin to set, the bubbles are trapped in, causing the baked goods to rise and be fluffy. This is exactly the principle behind soda bread — using baking soda and buttermilk to cause the bread to rise w0ith no yeast.
And, like so much cooking, you’re actually doing chemistry even though you think you’re channelling your granny!
In our Ask Peter series, executive chef Peter Gordon answers your curly culinary questions. If you're stumped over something food-related, send your question to email@example.com and keep checking in for answers. You can read more on Peter on his website, have a read of his Ask Peter articles or check out his recipes on our site.