You know what's great? Bringing home an armful of fruits and vegetables from the market, all bright, fresh, and ready to be tossed into salads, soups, and stir fries. You know what's not so great? Having a busy week and realizing later that the produce is wilting and rotting in your refrigerator. Properly storing fruits and vegetables is key to extending their shelf life, yes, but even that only goes so far.
So when the editor-in-chief of The Cooking Lab, the culinary research team behind the Modernist Cuisine books, said he'd found a better way to preserve fruits and vegetables, we knew we had to listen. (Hint: it doesn't involve any chlorine, irradiation or peroxide baths, and it's not blanching.)
It's heat shocking! As W. Wayt Gibbs wrote, blanching (briefly boiling and then plunging into cold water) can extend the life of certain plant foods, but it's not ideal because it "ruptures the cell walls of plants, causing color and nutrients to leach out" and "robs delicate produce of its raw taste."
Heat shocking is different. If you plunge produce into warm but not scalding water (anywhere from 105 F to 140 F), you won't rupture the plant cells: "Rather, the right amount of heat alters the biochemistry of the tissue in ways that, for many kinds of produce, firm the flesh, delay browning and fading, slow wilting, and increase mold resistance." (Scientists are still working out the details as to why exactly it works.) Gibbs writes that this method is ideal for firming potatoes, tomatoes, carrots, and strawberries; preserving the color of asparagus, broccoli, green beans, kiwi fruits, celery, and lettuce; fending off overripe flavors in cantaloupe and other melons; and increasing the shelf life of grapes, plums, bean sprouts and peaches.
How do you heat shock your fruits and vegetables? The process is simple:
Just let the water run from your tap until it gets hot, then fill a large pot of water about two-thirds full, and use a thermometer to measure the temperature. It will probably be between 105 F and 140 F; if not, a few minutes on the stove should do the trick. Submerge the produce and hold it there for several minutes (the hotter the water, the less time is needed), then drain, dry and refrigerate as you normally would.
Gibbs also notes the optimal temperature and time varies for each fruit or vegetable. Here are his recommended guidelines:
- Asparagus: 2 to 3 minutes at 131 F (55 C)
- Broccoli: 7 to 8 minutes at 117 F (47 C)
- Cantaloupe (whole): 60 minutes at 122 F (50 C)
- Celery: 90 seconds at 122 F (50 C)
- Grapes: 8 minutes at 113 F (45 C)
- Kiwi fruit: 15 to 20 minutes at 104 F (40 C)
- Lettuce: 1 to 2 minutes at 122 F (50 C)
- Oranges (whole): 40 to 45 minutes at 113 F (45 C)
- Peaches (whole): 40 minutes at 104 F (40 C)
Have you ever tried heat shocking? I'm anxious to try it this weekend and see how it goes.