A-Z of unusual ingredients: Buttermilk

Most food-related portmanteaus are logical. 'Cheeseburger', 'frappuccino' and even the latest craze of the 'cronut' (half croissant, half doughnut).

'Buttermilk' paints a more confusing picture though. Following the trend of creating a new food by melding two words, you could be forgiven for imagining lumps of butter floating in a jug of full-fat milk. It sounds pretty artery-clogging, but buttermilk is in fact far healthier than its name implies.

When cream is churned, it separates. The fat goes into butter, and the 'buttermilk' is the liquid left behind. Thick and milk-like, but without so much fat, it is rich in protein and more easily digested.

Different cuisines have focused on different properties of this magical ingredient. In the Deep South, buttermilk is used to tenderise chicken before frying. In India, it's mixed with spices and served as 'chaas' - a drink which cools the palette and aids digestion. And in Ireland, the acidity of buttermilk is used to react with bicarbonate of soda and cause soda bread to rise without the need for yeast.

Buttermilk was once hard to track down, but this versatile ingredient is currently experiencing something of a resurgence. Ivy House Dairy Farm's buttermilk sales have increased tenfold in the past year. And pots of buttermilk are cropping up somewhere between the crème fraiche and the yoghurt in more and more supermarkets - with Sainsbury's even stocking their own brand.

Ottolenghi uses buttermilk in a sauce drizzled over roasted aubergine, Anna Hansen uses it for a twist on the classic panna cotta, Oliver Dabbous poaches salmon in a buttermilk broth and The Hummingbird Bakery uses buttermilk in their red velvet cakes. But it's London's fried chicken movement which is giving this once-maligned dairy product a new lease of life, with joints like Chooks or Spit & Roast serving buttermilk-fried chicken as a signature dish.

When it comes to cooking with buttermilk, there's lots of mixed advice, due to the many different varieties of buttermilk, and their different purposes. The most intensely-flavoured, but by far the most elusive, variety is traditional, artisan-made buttermilk. Darina Allen, founder of Ballymaloe cooking school, explains how buttermilk used to be made on small, Irish dairy farms which didn't produce enough milk to churn butter on a daily basis. "They'd save up the milk over two or three days until they had enough to churn, so by the time the buttermilk was made, it would immediately have a very ripe flavour," she explains. "It was common back then, but it would be considered an acquired taste now."

Whether the fermentation happens at the milk stage, or whether the buttermilk is left to ferment after it's churned, the important part is that the aging process produces lactic acid. This is what gives the buttermilk its distinctive, tangy taste, and also what allows it to react so ferociously with alkali ingredients, causing breads and sponges to rise. Supermarket varieties don't naturally-ferment the buttermilk. They introduce a culture and artificially-ferment it, which still creates high acidity levels and a tangy taste. Nothing on the nostril-stinging ripeness or traditional farm-made buttermilk, but effective nonetheless.

Failing farm-made or shop-bought buttermilks, there is always the option of making your own. Charlie Westhead, owner of Neal's Yard Creamery recommends putting a teaspoon of creme fraiche into a 500ml jug of milk in the evening, and leaving it in a 20°C airing cupboard overnight. "By the morning, it will have transformed into beautiful, live buttermilk." he says. The other trick is to add a teaspoon of lemon juice to milk. It's a good short-cut for raising the acidity levels of milk enough to switch it into a recipe which requires buttermilk to react with an alkali. But the lemon milk won't introduce the ripe, tangy flavours of real buttermilk."

So, it really is best to keep your eyes peeled for a farm or supermarket variety. But if it's not in a dairy aisle near you yet, then homechurning and home-fermenting may still be the best option.

Simple Soda Bread Recipe

500g plain flour

1 teaspoon bicarbonate of soda

1 teaspoon salt

425ml buttermilk

Preheat the oven to 200C.

Sift together the flour, bicarbonate of soda and salt.

Use your hand to furrow out a well in the flour, and pour the buttermilk into it.

Loosely knead the dough - you're not looking for smooth, elastic perfection - but more of a rustic feel.

Push the dough into a round circle, and use a knife to etch a cross into the top. Place the bread onto a dusted baking tray, and bake for 40-45 minutes.

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