Red oil – hongyou 红油 – is the heart of Sichuan cuisine.

Sometimes you see it sold in teeny tiny bottles. And by “sometimes,” I mean that you would never see this in Sichuan itself.

That’s for two reasons.

The first is that making red oil is a good way to recycle used but reasonably clean oil. I’m not talking about sludge oil–the infamous 地沟油 that dishonest dealers buy from restaurants and factories “perk up” with such tasty substances as laundry detergent. I mean oil that has been used a few times for deep frying, and is now looking a little tired. Restaurants go through a lot of oil, and the stuff is expensive. Even if they don’t admit it, most of them will make their hongyou out of these leftovers.

The second is that hongyou is in everything, on everything, or both. You fry with it, spoon it over cold dishes, and use it to toss noodles. Hongyou is what gives many Sichuan dishes their characteristic taste, feel, and of course–color. Buying hongyou in tiny bottles would make as much sense as buying water in tiny little bottles.

But enough social commentary, how do you make the stuff?

For readers who do not know, I am in China in a culinary trade school. We spent a whole afternoon on red oil. There are basically three parts:

1. Deep fry a big pile of vegetables in the oil. These are all fragrant greens: Chinese onions (similar to leeks), garlic shoots, cilantro, and ginger would be a good start, but you can use anything that will give a flavor you like. And I mean a big pile — roughly the same volume as the oil itself. Add a few handfuls of Sichuan peppercorns, and you can also add a few spices like star anise–I sure would. The vegetables are all torn by hand and fried at a low temp until the water is gone. They’ll be strained out later. Keep the temperature low–you don’t want to scorch the vegetables or spices.

2. Prepare a mix of chili powders. Naturally this is key. We used three for a specific mix of heat, color, and texture. In volume, the powder should be about 1/3 of the oil. Lightly fry the powder to bring out the fragrance, and allow to cool. (Note that frying a giant pan of chili mix will make your kitchen extremely “fragrant.” Be prepared to apologize to the neighbors.) Mix in a few spoons of cold oil before you add the hot oil.

3. Add the hot oil to the powder. Strain out the vegetables from the hot oil and slowly ladle it in to the powder mix. Make sure not to scorch the chilis, and don’t cook it. Other oils you cook, but not this one. At this point, add a couple of pieces of rock sugar (for consistency, not taste), and stir in crushed fried peanuts and white sesame (since the oil is hot, you don’t need to toast them).

Let the oil sit overnight, or preferably longer. In fact, the longer this sits the better it tastes, and as long as water is kept out it never goes bad. We keep ours in a giant, loosely covered stockpot in the back of the room

Your reward is a deep red oil, with a complex roasted chili taste, and an undertone of fragrant onion. It’s so good that many cold dishes like crushed cucumbers, or suanni bairou 蒜泥白肉, or this liangpi I had yesterday are flavored with this oil and little more–plus the crunch from the chili/peanut mixture at the bottom.

Do you have a favorite Sichuan dish that you would like me to explain? Add a comment to let me know!