The Science of Gravy: Wylie Dufresne on Emulsions & His Advice for Better Gravy

The Science of Thanksgiving

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There's something a little magical about a really good gravy. From drippings, a little flour and some stock comes a bubbling pot of liquid gold, ready to be poured over turkey, mashed potatoes and everything in between. But have you ever wondered what's going on inside the pan when you make gravy? We turned to chef and Harvard food science instructor Wylie Dufresne for a scientific explanation, as well as his advice for making better gravy on Thanksgiving and beyond.

What is an emulsion?

An emulsion is a mixture of two liquids that would ordinarily not mix together, usually things like oil and water. In an emulsion, tiny droplets of one of the liquids become very evenly dispersed in the other liquid, whether it be oil in water or water in oil. An emulsifier is a substance that helps the two liquids come together and stay together. It's generally referred to as a surface active agent that promotes the formation of an emulsion, meaning — and this isn't a very scientific term — it helps the two liquids "talk to each other" and get together.

From a scientific perspective, what's going on in the pan when you make gravy?

When we're talking about gravy, you're probably starting with a roux, but flour is not an emulsifier. Flour is helping to thicken the stock in your gravy. It's increasing the viscosity of the water phase of the stock and that's helping to stabilize the emulsion. And there are probably some proteins found in the stock, if you're using an animal-based stock like chicken or turkey, and protein is an emulsifier. The gelatin in the stock is a pretty solid emulsifier, so you're getting some help there.

What's your approach to making gravy?

You know, I'm kind of a traditionalist when it comes to gravy. When I make my gravy, I pull the rack out of the roasting pan that I used to roast the bird, pour off all that grease, add a little flour to my pan and move the pan onto the stovetop. Over medium heat, I cook the flour, then I add turkey stock and deglaze, scraping up as much as I can. I transfer all of that to a pot and cook it on the stove, where it can reduce and thicken. I take it out of the roasting pan because it's kind of unwieldy and hard to work with, but I want all that good stuff that's stuck to the bottom of the roasting pan.

Any advice for making better gravy?

I would be careful about making sure that the solids at the bottom of the roasting pan don't burn. You can throw some vegetables in there, maybe for the last hour that your turkey is roasting, add some chopped onions, carrots and a little bit of garlic. As those vegetables cook, they'll release water and that water can help deglaze the pan and keep the drippings from burning.

And you can scoop out those vegetables later and use them in your sauce. You scatter those onions across the bottom of the pan and they get imbued with the turkey drippings and fat. Then those onions can go into your sauce and be strained out later, just to add another layer of flavor. The more layers you add to a sauce, the deeper it will be, the more complex it will be, and the more delicious it will be. It all depends on how hard you want to work!

The turkey you can kind of let do its things for hours on end while you're drinking red wine, but the sauce requires your attention — but the rewards of that hard work can be fantastic.

More from Wylie Dufresne:

Visit his restaurants: wd~50 and Alder
→ Learn about food science online from Wylie & other chefs: Harvard edX Science & Cooking: From Haute Cuisine to Soft Matter Science

(Image credits: Travis Huggett; Emma Christensen)

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