"I have heard chefs on TV and in books say that combining both oil and butter in a skillet when you sauté lets you heat the butter to a higher temperature without smoking. Is there any truth in this?"
The idea is appealing: butter offers great flavor but smokes and turns acrid at a relatively low temperature. Meanwhile, most neutral oils have a much higher smoke point, but are lacking in the flavor department. By combining the two, you end up with a mixture that has the flavor of butter, but allows you to sear at higher temperatures than you ever could with pure butter.
But does it really work? Let's find out.
First off, let's set our baselines.
I put a pat of butter in a cast iron skillet, turned up the heat, then cooked it, swirling the pan gently to attempt to even out any hot spots, until it started to lightly smoke.
Wisps appeared right around the 375°F range, with full-on billowing occurring by the time it hit 400°F. At 450°F, it was smoking so much that I was afraid it would catch fire, so I halted it.
Next, I heated up pure grapeseed oil—an oil known for its neutral flavor and high smoke point.
It got all the way up to 490°F before it started producing smoke.
For the final test, I combined both oil and butter in a single skillet. If the theory is correct, it should start to smoke somewhere between 380 and 490°F.
Uh oh. Wisps of smoke started appearing at 375°F.
Unfortunately, it's simply not true: a butter-and-oil mixture will start to smoke at the same temperature as butter on its own.
Why is this? Well, let's take a look at what butter is to get an idea. Butter consists of three distinct phases:
- Fat: Butter consists mostly of fat—around 80 to 83%, in fact, depending on the brand or specific processing. This fat, in turn, is not composed of a single type of molecule, but is actually a homogenous mixture of many different fat molecules, each with a slightly different shape and size.
- Water: Most butters are around 15% water by weight. This water is emulsified into the solid butterfat in its cold state.
- Protein: Aside from minute amounts of milk sugars and minerals, the remaining couple of percentage points are made up of milk proteins—you can observe them as the white scum that floats on top of melted butter. It's mostly these proteins that give butter its distinct flavor.
So what happens when that butter is heated up in a skillet? At low temperatures, it starts to soften. Because each of the varying fat molecules becomes a liquid at a different temperature, butter will slowly soften over a wide temperature range until it is completely liquid at between 90 to 95°F. Once melted, the water phase will separate out and form a distinct layer on top of which the butterfat floats. As you heat butter in a skillet, it's that water content evaporating that causes butter to foam and sputter at the early stages of heating.*
*Incidentally, swirling the pan as this happens can help encourage the water to evaporate at a more regular pace instead of in sudden leaps and spurts, minimizing the amount of splattering that occurs.
Once the water has evaporated, you're left with pure butterfat along with those proteins. And when it comes to smoking, it's those proteins that are the culprit. Once they start to hit that range between 300 and 350°F, they start to break down rapidly. By the time you're at 375°F, they're in full-on vaporization mode, flying off into the air in the form of smoke.
As far as those smoking proteins are concerned, it doesn't matter what medium you're cooking them in, whether it's butterfat or vegetable oil. They're going to react and smoke regardless.
Get rid of those proteins by skimming them off as you would when making clarified butter or ghee, and you're left with pure butterfat, which can be heated to nearly 500°F before it begins to break down and smoke, though clarified butter doesn't have the same flavor as butter.
There is, however, an advantage to cooking with a mixture of oil and butter. Though the milk proteins will still burn, if you cut the butter with oil, they'll at least be diluted, meaning that you won't have as much blackened flavor in that mix.
In the end, it really depends on what you are cooking. For things like steak and pork chops, I like to use pure butter or a mix, because those dark milk proteins actually accelerate the browning of meat, and I personally don't mind the slightly bitter, charred flavor of dark, dark butter. If, on the other hand, I'm frying, say, a piece of fish or chicken, or perhaps searing some delicate vegetables like squash or eggplant, I'll probably go with straight oil so that the flavor of the darkened buttered doesn't overwhelm them.