TRANSCRIPT Ep 03 CURDLED
Welcome to The Simmering Chef.
Cooking with a smidgen of anger, a pinch of crass, a dollop of irreverence, a sprinkling of science, and a handful of spice.
Thank you, everyone, for listening today. A big shoutout to The Simmering Chef’s new subscribers. You guys are awesome! Your support means a great deal, so thank you very much. This week, we’re looking at curdled dairy.
By the way, we’ve gone international with today’s query. Very exciting. Let’s get started.
Dear The Simmering Chef,
Lemon is one of my favorite flavors. If I could add it to everything I eat, life would be spectacular. But every time I add lemon juice to my pasta sauce, it curdles, making it look unappetizing. What do I need to do? Is it the heat?
Curdling in Wellington, New Zealand
Dear Curdling,
You know the saying, “that look could curdle milk?” To be honest, one of dairy’s proteins, casein, is a real wimp. Curdles at the slightest change of heat or pH levels. Sure, it gives the appearance of being free and easy, floating around in tiny bodyguard bubbles called micelles while lazily bobbing around milk's other colloidal components of sugar, water, and fat. Those bodyguard bubbles are negatively charged, repelling anything from clinging to them while keeping all the various molecules equally distanced. They are true crowd control.
Casein thinks it’s a chill protein, really laid back, and in its arrogance thinks, “You can’t touch me because I am surrounded by this badass bodyguard bubble that repels everything and keeps me from bumping into any of you!” Poor casein. Change the least little thing about that liquid the micelles floats in, and the bodyguard dissolves, forcing the protein to wet itself and clump together with the other casein protein molecules into shivering masses of curdled mess in hopes that there is safety in coagulated numbers.
Now, for us, curdling isn’t always bad. It’s how we make cheese and yogurt. But when that’s not what we want, knowing what causes the curdling and how to prevent it is a win all around.
As you noticed, heat speeds up curdling, but the big culprit here is acid. Remember chemistry? Using the 0 - 14 pH scale is how we measure food’s acidity.
Lemon juice lands between 2 and 3 on the pH scale, meaning it’s super acidic. Milk at 6.7 to 6.9 lands in the pH scale’s neutral area and curdles when it is lowered to 4.6. Throw any acidity into a neutral pH, and it naturally becomes more acidic. Higher acidity messes with the micelles’ bubble structures by weakening and dissolving them and neutralizing the negative charges’ repelling function. Look at it this way. Acid is the micelles’ kryptonite. Add it, and it’s “Buh-bye bodyguard.” The casein protein leaks out, and with nothing repelling these protein molecules, they cling to each other and coagulate. We call that curdling.
Here’s an experiment. Throw acid into cold or room temperature milk and notice how long it takes for it to curdle. It should take a couple of hours. Throw acid into hot milk, and the curdling process is immediate because those molecules are moving around really fast.
Here’s an image to help you. When that milk is hot and you throw lemon juice into it, what you are seeing is milk’s calcium crying out in pain and lactic acid’s tear production increasing because the lemon juice’s citric acid is running around and beating the shit out of them. Quite an image, huh?
Your gig is knowing how to stabilize the milk so it doesn’t curdle when you add the acid. Here are a few ways to accomplish that. You don’t need to do all of them simultaneously, and some might work better in different applications. Ultimately, your goal is for a smooth, silky sauce. Let’s take a look.
1) Don’t boil the milk. Matter of fact, be gentle here. Gently heat your milk over the burner, giving the liquid a fighting chance.
2) Lower lemon juice’s acidity by whisking in some baking soda. This raises its pH level to above 4.6, effectively neutralizing its citric acid and preventing the milk from turning too acidic. Sadly, this will also affect flavor.
3) Stir your lemon juice into cool or room temperature milk before cooking. This is one of my least favorite methods because once you heat the milk, it curdles immediately. This works well for cold applications.
4) Adding a roux to the milk, essentially making a béchamel sauce, stabilizes the milk, but it might not be the flavor or texture you want in your sauce. Other thickeners, such as cornstarch and arrowroot, work too. Consider the application and the final result you want to achieve before using this method.
5) Do what I do. Just before serving, I stir in lemon zest to boost flavor. The skin’s essential oils give the lemon pop. If your goal is sour, try deglazing with lemon juice and reducing it to almost dry before adding and reducing your cream. Pump up the lemony flavor with zest.
There you have it. Good luck and have some fun when making your sauce. Oh, side note. "Scientific American" has a superb milk-curdling activity for young and old. The link will be embedded into the transcript. I do want to mention that different acids act differently on milk. The publication has you use both lemon and pineapple juices. As violent as lemon juice is on milk, pineapple is a terror, hacking and shredding those poor bodyguard micelles to pieces. So remember, as you practice the gentle art of cooking, it can be terribly violent too.
Before we leave each other today, a little shameless plug encouraging you to subscribe to The Simmering Chef on Substack. My subscribers receive a non-habitual culinary communication focusing on a seasonal fruit or vegetable with a corresponding recipe, information, and hopefully a little humor. I’ve been told it’s landing in the spam folder, which seems apt.
As always, fail brilliantly and eat well.
The Simmering Chef
