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13 May 2013
Dua, Vietnamese fermented mustard greens
When mẹ, my mother-in-law, pronounces this dish, it sounds like “awe” with a ‘dz’ prefix (like we hear in 'adze'), so it sounds like “dzawe” to my non-Vietnamese ears. She’s been making it forever, and though we’ve asked her several times to show us how to make it, it was only after my wife and I went to Vermont’s first fermentation festival that I pressed her to share her way of making it. Like many things she cooks, mẹ says it’s easy and that it can be prepared in a number of ways. Once I get the hang of a dish, this perspective is great, but it’s difficult to learn a new dish when most questions are answered by, “It doesn’t matter,” or “You can do whatever you want.” On the other hand, such ease with substituting or changing ingredients shows how comfortable and familiar some people are with dishes (rather than recipes) that are close to them; they see infinite variety in secondary ingredients, which keeps the same dish interesting year after year.
So many fermented recipes follow a similar pattern, and dua is another. Using mustard greens, which are a thick ribbed and heavy-fleshed leaf, dua differs in just a few ways. First, the washed leaves are separated and laid out to dry and wilt a little. Mẹ recommends an overnight wilting period but in the hot sun it might be only a few hours. Next, the leaves are cut into smaller pieces to make them easier to eat when they’re done fermenting, but they can be left whole, especially if you plan to cook the dua with pork, which is a favorite way to cook it. When I’m making sauerkraut I use the pretty standard ratio of 3 tablespoons salt for 5 pounds cabbage, but dua differs a little in that there’s not a lot of water to pull out through osmosis, so a brine is typically used. To make the brine, I bring water to a boil, add salt, and let it cool to room temperature. A few tablespoons of kosher or sea salt in a few quarts of water is a pretty good ratio – the brine should taste salty. Put all the wilted greens into a big glass or ceramic bowl or crock, and cover with the brine. I put a plate on top to keep all the greens submerged, and a water-filled bowl on top of the plate. A sliced onion is a pretty standard addition, and mẹ sometimes adds garlic, chili peppers, or ginger.
The important thing is to keep the greens submerged because the fermentation occurs in anaerobic conditions and exposure to air can cause less beneficial molds to form on the dua. When mẹ makes it she frequently skims a layer of mold off the top of the brine; I prevent that by keeping a plate and bowl on top, ensuring that the mustard greens stay submerged. And, of course, when you begin, make sure all your containers are clean – I rinse everything in very hot water, and if a container has been used for something that’s left residue of some kind, I first rinse it with boiling water.
When fermenting things the first few times my confidence sometimes wavered and it seemed beyond my reach. But I thought about our early human history as a refrigerator-less species, and figured that I could figure it out (with the help of a few books and conversations with friends.) So I hope you'll give it a try; ferment something and eat like most people did in those years people lived without electricity. Here’s my simple 1,2,3 to make dua, Vietnamese fermented mustard greens:
1. Wash a big heap of mustard greens and spread the separated leaves out to wilt, overnight. Cut into smaller pieces, if desired.
2. Bring a pot of water to boil and add salt. Stir to dissolve and let cool. Use three or four tablespoons of kosher, sea, or other non-iodized salt in the pot. It should taste salty but doesn’t have to pucker your eyeballs.
3. The next day, put the wilted greens into a big pickle jar, ceramic crock, or glass bowl. Cover with brine.
4. Put a plate on top. Put something on top of the plate to keep it weighted down.
5. Let sit for a week or so. Dua will turn pale and yellowish. When done, drain off brine, and store in fridge, covered.
6. Eat with rice, as a cool accompaniment to spicy foods, or by itself.