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5 Buttermilk Questions You Were Too Embarrassed to Ask

By the editors of Cook's Illustrated

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For example, what's the best way to know if buttermilk has gone bad? We've sniffed out all the answers for you.


In the old days, buttermilk was simply the liquid left behind after cream was churned into butter. As unpasteurized cream sat “ripening” for a few days before churning, naturally occurring bacteria caused it to ferment by converting milk sugars into lactic acid, which made the resulting buttermilk mildly sour and slightly thickened.

But since virtually all milk and cream is now pasteurized at high temperatures, a process that kills off those bacteria, most buttermilk sold today is cultured buttermilk, made by reintroducing lactic-acid bacteria to pasteurized skim or low-fat milk. Often, it’s also reinforced with salt and thickeners like carrageenan and starch.

  Butter Milk


We use buttermilk in some baked goods, as it adds a subtle tang and increases the rise when it interacts with baking soda. We also use it to brine chicken before frying and as a base for several other meat marinades.


When we asked this question of the folks at the dairy farm that produces the buttermilk we use in the test kitchen, they told us to consume their product within five to seven days after opening. However, guidelines from agricultural programs at various universities extend that period to two weeks. Then there’s our experience, which has shown that refrigerated buttermilk won’t turn truly bad (signified by the growth of blue-green mold) until at least three weeks after opening. That it can last this long is not surprising, since buttermilk is high in lactic acid, which is hostile to the growth of harmful bacteria. That said, we wondered if the flavor of buttermilk changes the longer it’s stored. To find out, we held a series of tastings, comparing pancakes made with freshly opened buttermilk with those made with buttermilk that had been refrigerated for one week, two weeks, and three weeks. We found that as time went on, the pancakes tasted increasingly bland.

Here’s why: The bacteria in buttermilk produce lactic acid and diacetyl, a flavor compound that gives buttermilk its characteristic buttery aroma and taste (diacetyl is also the dominant flavor compound in butter). As time passes, the buttermilk continues to ferment and becomes more acidic. The abundance of acid kills off virtually all of the bacteria that produce the buttery-tasting diacetyl. So three-week-old buttermilk will retain its tartness (from lactic acid) but lose much of its signature buttery taste, giving it less dimension. The good news is that there is a way to prolong the shelf life and preserve the flavor of buttermilk: Freeze it.


First of all, don’t worry if you’re halfway through a recipe that calls for buttermilk before you realize you don’t have any in your fridge. You can make “clabbered” milk, a widely recommended substitute for buttermilk in baked goods.

The usual approach is to stir lemon juice into milk (1 tablespoon per cup) and let the mixture sit for 10 minutes to “clabber” (or thicken) before proceeding with the recipe. But after following this method and closely observing what transpired, we discovered that clabbering milk doesn’t give it the smooth, thick consistency of buttermilk. Small curds formed almost instantly, but after a 10-minute rest, most of the milk had not thickened at all. And more waiting still didn’t give clabbered milk the consistency of buttermilk.


It turns out that when lemon juice is added to milk, the citric acid changes the electrical charge on the dairy’s casein proteins, causing them to coagulate tightly into clumps. On the other hand, the Lactobacillus bacteria added to milk to produce commercial buttermilk remove some of the sugar molecules bonded to the proteins, allowing them to form a gel that gradually becomes thicker over time.

THE EXPERIMENT: So, does waiting after treating milk with lemon juice impact its baking properties? To find out, we made multiple batches of biscuits and buttermilk pancakes: one set with clabbered milk that had rested for 10 minutes and one set in which we mixed the milk into the batter immediately after adding the lemon juice. All of the biscuits and pancakes were virtually identical in appearance, flavor, and texture.

THE RESULTS: Adding lemon juice to milk simply acidifies it, allowing the leavening in the batter to do its job—the same role played by buttermilk. Since this change happens immediately, you can safely skip the resting time.


The acid in buttermilk helps baking soda do its job in recipes like biscuits and pancakes. To substitute regular milk in those recipes, the most common approach is to use clabbered milk, which we described earlier in this post. Though lemon is usually an acceptable flavor, we’ll admit the questionable appeal of vinegar pancakes.

In researching alternatives, we discovered one that we’d never considered: cream of tartar, an acid with a less noticeable flavor that’s often used to stabilize whipped egg whites.

  Cream of Tartar

When we used a mixture of cream of tartar and regular milk (1 1/2 teaspoons of cream of tartar for each cup of milk), our biscuits and pancakes came out just as lofty and light as those made with buttermilk, with no off-flavors. But there was one problem: Unlike lemon juice and vinegar, powdery cream of tartar can clump when you stir it into milk. The solution? Whisk the cream of tartar into your dry ingredients instead.

When you don’t have buttermilk on hand (and the tartness of regular milk mixed with lemon juice isn’t ideal), cream of tartar is an excellent alternative.

 Best Buttermilk Pancakes

RECIPE FOR MEMBERS: To create a buttermilk pancake recipe with a tangy flavor and fluffy texture, we added sour cream for flavor and cut back on leaveners to keep the pancakes from rising too high and then collapsing. The result is a pancake recipe for light, fluffy pancakes with the trademark buttermilk tang.

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