Wok Skills 101: Passing-Through

Passing-through (jau yau/走油 or jau shui/走水) is a defining feature of many Chinese restaurant dishes. And while you may not be able to discern it in a stir-fry as easily as the smoky aroma of wok hei—chances are good that some element of that dish has been "passed-through" first. It’s generally a preliminary or intermediate step, not a standalone technique used in isolation to make a dish.

The Chinese phrase jau yau (走油) literally translates to “passing through oil” (jau means “pass” and yau means “oil”). It is a means of par-cooking ingredients prior to building a finished dish—a foundational cooking technique that can drastically improve the texture and flavor of meat and vegetables. The method involves a pool of hot oil, in which ingredients are cooked rapidly and then promptly removed before continuing with the rest of the dish. 

Jau shui (走水) translates to “passing through water.” The technique is virtually identical to jau yau, except for the cooking medium.  

As an intermediate step, passing-through—especially in oil—is often practiced in Chinese restaurant kitchens and industrial settings, where splatter, mess, and using large quantities of cooking oil aren’t much of a concern. But that doesn’t mean you cannot and should not pass-through at home, too: the benefits of the technique can far outweigh the costs, and ultimately help you cook better food.

The Benefits of Passing-Through

Passing-through provides uniform heat in a short burst, shortens the time to subsequently stir-fry by par-cooking ingredients and driving off moisture, and offers all kinds of flavor and textural advantages. In restaurant kitchens, it is most common to pass-through using oil, but at home you can produce similarly effective results by passing-through in water too. Here's a closer look at its many benefits:

Passing-Through Drives off Moisture in Proteins

Dunking food in hot oil or water drives off excess moisture. Take beef, for example. Passing the protein through oil or water partially dehydrates the surface as the proteins contract. You see this when the oil sizzles and spatters: that’s water leaving the meat (you see it less in water, as the exuded water from the meat moves into the pool of simmering water). The result? The meat cooks, but it’s also better suited to stir-frying down the line. “Meat tends to absorb a sauce more readily when you pass it through,” says chef Brandon Jew of Mister Jiu’s restaurant. And because you’ve driven off the initial moisture, you’ve concentrated the flavor of the beef and reduced the chances of your stir-fry losing heat and becoming soggy or water-logged. If you were to cook the meat from raw in a stir-fry, that extra moisture would suppress the temperature of the wok, and the meat would end up boiling or steaming instead of browning.   

Passing-Through Shortens the Overall Cooking Time

Par-cooking ingredients means you spend less time cooking those ingredients later on. For a stir-fry—where speed and high heat are essential to success—that time reduction is crucial. By keeping that stir-frying step brief, you lower the risk of steaming the meat and watering down the dish, or overcooking the meat due to prolonged cooking. “Lobster is a great example,” says Serious Eats contributor and chef Lucas Sin. “It doesn’t cook for a very long time in a stir-fry dish like [Lobster Yee Meen (龍蝦伊麵)], so passing it through—especially in oil—is important” to minimize the risk of overcooking.  

Passing-Through Adds Flavor and Tempers Undesirable Flavors

Passing-through oil is basically small-batch deep frying. In other words, you get all the benefits of frying, including roasted, Maillard flavors, and a little bit of richness. But even if you pass-through water, the technique has another benefit: it removes unwanted bitter or otherwise harsh flavors. “Cantonese people don’t like grassy, gamey flavors, so passing-through is a good way to remove those notes,” says Sin. Good examples are lamb and duck, but even kale, Brussels sprouts, and cauliflower can benefit from passing-through because it removes their bitter, astringent flavors.

Passing-Through Improves Texture

By par-cooking meat, passing-through typically ensures a tender, succulent texture because of the uniform heat supplied through conduction of oil or water. For vegetables, the benefits are more varied: for plants like snap peas and snow peas, passing-through preserves their crisp texture and vibrant color (just like blanching). In other cases, passing-through transforms the texture entirely. “We always pass eggplant through [oil] at the restaurant,” says chef Brandon Jew of Mister Jiu’s in San Francisco. The oil drives off moisture and turns the eggplant blistered and spongy to the point that it soaks up any sauce or seasoning while maintaining a cohesive shape and bite.     

Passing-Through Allows Optional Velveting of Proteins

Passing-through often (though not always) involves an additional technique called velveting: The practice of coating proteins in cornstarch, liquid (water, soy sauce, shaoxing wine), and sometimes egg white or other ingredients. The starch acts as a protective coating, and is thought to “seal in” the flavor of the protein and to produce a silky, tender texture. Velveting is a fundamental technique in Chinese cooking, widely employed in Chinese restaurants because of these benefits.

In practice, we can think of the cornstarch marinade as a batter that gelatinizes and sets into a semi-rigid structure when it’s cooked in hot oil—basically a very thin fry coating. The protective film is thought to minimize sticking to the wok during stir-frying. The coating also tends to bind more water if it is cooked further in liquid—thickening and clinging to any sauce that you add to it.

For example, in a dish like beef and broccoli, the beef is typically velveted before stir-frying with broccoli (the broccoli may be passed-through water beforehand as well). As you add liquid to the beef and broccoli, the surface starch often thickens that sauce, giving more body to the finished dish. Finally, velveted proteins tend to brown more readily in stir-fry dishes, since the initial velveting step binds most of the water exuded from the protein; this is because the water gelatinizes the starch, which dries the surface out as the starch network sets into a more rigid structure. 

To be clear, while many proteins are routinely velveted, you don’t usually velvet vegetables. And there are also cases where you would want to pass-through a protein but velveting is undesirable. “With a super delicious, marbled beef like grass-fed wagyu, you don’t want to lose any of that flavor,” says Lucas Sin. Velveting would mask and diminish those flavors, so Sin opts for cooking it raw. For dishes like shrimp-fried rice, where cooks want to highlight the fresh, briny flavor of the shrimp, velveting can be also counterproductive. It’s better to pass the shrimp through without a velveting step so that their plump, shrimpy bite shines through.

What Makes a Wok Ideal for Passing-Through?

In a restaurant, it’s easy to transition from passing-through to cooking using another method all in the same wok due to the high output of a professional wok burner. But at home, with limited heat output and limited resources, passing-through in a single wok can be more complicated. It might make more sense to pass ingredients through in a small pot on the side.* Still, there are benefits to passing-through in a wok—even at home.

*In reality, many restaurants just use a deep fryer to pass-through all their ingredients. It’s simpler, more efficient, and safer.

Shape

The wider area of a wok makes it easy to transfer ingredients in and out without wasting time fishing around the way one often does in a straight-sided pot. And given the wok’s convex shape, you don’t need to use as much oil or water. The sloping sides also limit mess and splatter, since the wok covers a larger area over your stove.

Material

The thin metal construction of a wok means that the wok heats quickly. That speed is crucial if you are cooking a dish in stages and have to reset your wok between cooking components. You can heat oil or water in minutes, pass-through ingredients, remove them, dump the oil or water, then clean and quickly reheat the wok again to continue cooking.

How to Pass-Through

Select a Cooking Medium: Oil or Water

Oil is the medium of choice in a professional setting: it offers superior heat conduction, a little more richness, and sometimes that “deep fried,” Maillard flavor if you’re cooking at higher temperatures. For an even meatier taste, you can supplement some of the oil with lard. But oil can be messy, there can be splatter, and for home cooks who don’t cook regularly, using oil for a single recipe step may not be worth the cost and effort.

Water is a simple, affordable, and more home-friendly option than oil. For vegetables like snap peas, passing-through water is preferable: You don’t need the higher temperature capacity of oil to briefly blanch the peas. And even for velveted proteins, water seems to produce results that are often just as good as oil. “When I do the velvet technique, I do not use the oil passing technique,” says cookbook author and wok expert Grace Young. “I prefer the water. It is just as delicious, and I think it actually gives a cleaner and fresher taste.” In a side-by-side comparison, Serious Eats contributor Shao Z. found that the differences between oil-velveted and water-velveted chicken were nearly imperceptible. 

Determine the Amount of Liquid

The volume may vary from recipe to recipe, but generally one and a half to two cups of liquid (oil or water) is sufficient to pass-through most items. For bigger, bulkier ingredients like lobster, you may need more liquid to cover.

Optional: Marinate or “Velvet”

Choosing to marinate or velvet is dependent on the flavors or textures you’re aiming for. Vegetables typically don’t require either step. If you choose to velvet, Grace Young recommends marinating proteins for at least 30 minutes. “I will marinate the chicken, the beef, shrimp in a mixture of cornstarch, egg white, and a tiny bit of rice wine,” Young says. “After all the cornstarch has dissolved, then I add a little bit of oil to coat the mixture and then I let it sit in the refrigerator uncovered for about 30 minutes.”

• Starch options: Cornstarch, potato starch
• Liquid options: water, broth, soy sauce, egg white, sesame oil, vegetable oil 
• Seasoning: White pepper, five spice powder, salt, sugar

Heat the Cooking Medium

What temperature is best for passing-through? If you’re using water, you really only have one option— roughly its boiling point, or 212℉. For oil, the recommended temperature range is slightly higher—up to 300-325℉. At this range, the oil is hot enough to cook the food but generally not hot enough to brown it, which would happen in a true deep-frying scenario. (Many modern Chinese restaurants have dedicated deep fryers, which obviates the need for passing-through in a wok. “We pass everything through the deep fryer. It’s so much easier,” says Lucas Sin.) 

Pass-Through and Cook

Cooking generally shouldn’t take more than a minute or two. Remember: you’ll be cooking these items later on, so the goal here is to par-cook, not to fully cook. 

Remove Ingredient, Pour Out Cooking Medium, Proceed

At this point, you must remove your par-cooked products and set them aside. In Chinese restaurant kitchens, cooks often empty the contents onto a perforated skimmer set over a container to catch the oil. Alternatively, they remove the ingredients from the wok with a strainer and then pour the oil off into a dedicated container; if using water, you remove the par-cooked ingredient, and then just discard the water. Finally, it’s important to reheat the wok and re-season the wok after passing-through with water by heating it with a bit of oil before proceeding.

Tools for Passing-Through

Chinese Spider (zhàolí/笊籬)

The Chinese spider is a woven, wire-mesh basket attached to a wooden handle. Its relatively wide area is ideal for larger, indelicate items like potatoes or dumplings. Due to its sharp edges and woven construction, it’s not great for more delicate, fragile foods that could snag on the sharp edges of the spider, or get caught in the mesh. For this reason, this tool is better for blanching or passing-through vegetables rather than velveted items.

Metal Spider

Like the Chinese spider, the metal spider typically consists of a basket-like saucer attached to a metal handle. Instead of a wire-mesh weaving, the saucer features concentric circles of smooth metal. This tool has all of the benefits of a traditional Chinese spider, but it’s better suited to handle velveted items since they're less likely to get stuck in it, and it's easier to clean.

Perforated Oil Skimmer

If you’re trying to pass-through large batches of food, this tool might be the best option. It’s basically a large, flared, perforated metal saucer attached to a sturdy metal handle. Since the saucer is a single piece of metal, there are no places where food could snag or get trapped. In many cases, the skimmer also doubles as an oil strainer in professional kitchens: Cooks can pass-through food, then dump the contents into the skimmer set over a large container.

Strainer and Heat Safe Bowl

If you opt for passing-through oil, it’s helpful to have a landing space for the excess hot oil left over after cooking. A fine-mesh strainer set over a stainless-steel bain marie container is a popular setup because it’s stable and heatproof.