Hello, I’m Andrea Castillo and this is Seasonal, a newsletter that connects you to the Bay Area food system, one fruit and vegetable at a time. Each post highlights the most interesting aspects of one seasonal fruit or vegetable grown and harvested around the Bay Area. Seasonal is a public good, and all past and future posts are free to read, but if you want to support my quest to deepen our connection to food and contribute to building a stronger food community, please consider becoming a paid subscriber for $5/month. Find me on Instagram at @seasonalbayarea or e-mail me at to share your feedback and suggestions, I’d love to hear from you. If you’d like to unsubscribe, click the link at the bottom of this post.

This week we nerd out on arugula (available year-round).

Arugula: the leafy green that is a popular salad ingredient and isn’t a lettuce. Arugula, or rocket if you’re British, makes an excellent base for salads, and, for some reason—likely rooted in associating salads with lettuce—I thought it was in the lettuce family. Well, it’s not. Arugula has much more in common with brussels sprouts, puntarelle, or cauliflower than it does with any type of lettuce. How come? Because, like them, it’s also a member of the expansive and ever-present Brassica group of vegetables that includes radishes, cabbages, and broccoli. The fact that arugula is a Brassica explains the pungency and pepperiness right away: just like radishes, arugula’s glucosinolate compounds defend it against pests and transform into isothiocyanates in our mouths when we chew them, yielding that signature peppery experience associated with arugula and several other Brassica vegetables. (To read more about the fascinating science of glucosinolates, see radishes.)

Pepperiness sets arugula apart from many other salad greens when it comes to taste. But when it comes to logistics, it’s the unique physical properties of this potent green that place it in a world of its own. I’ll go as far to say that the physiochemical properties of arugula have transformed entire food distribution systems.

Let me explain.

water as structural support

Like any other fruit or vegetable, arugula needs water to live and sustain itself. Water literally shapes leafy greens, and they keep their crisp quality so long as there is ample water in their plant tissue. Plant cells store most water in the vacuole, a large component that takes up at least 80% of the available real estate inside a cell. All that water creates pressure—what plant biologists call turgor pressure. Full cells press against each other, and, together, they create a nice, sturdy structure. When water is no longer available to the plant, those vacuoles lose their water, shrink, and, much like a leaky and uncomfortable air mattress, are no longer able to provide structural support. As vacuoles deflate, arugula wilts. Fast. Faster than any other leafy green.

One reason arugula wilts is transpiration. Arugula, like all plants, absorbs nutrients and water from the soil. As that nutrient-rich water moves through the plant, it nourishes cells and helps vacuoles stay nice and full. Eventually, that water evaporates, cooling the plan—this transpiration process continues even after harvest. Without water to sip on, harvested arugula depletes its water reserves. Its vacuoles get softer and emptier and, as transpiration continues, arugula wilts on its way from farms to stores. Transpiration isn’t unique to arugula—all plants continue transpiring and lose water after they’re cut. What is unique to arugula is how quickly it respires.

stress eating

Respiration is how plants eat: as they consume the nutrients they absorb, they emit CO2. Like transpiration, respiration is another reason arugula degrades post-harvest. Winter squashes, for example, can last for several months and kale can last for a month if stored right, but arugula taps out after a few days, max a week. What’s going on with arugula? Stress. When we harvest leafy greens, we stress them out: they no longer have a steady supply of water and nutrients so they have to tap their internal food reserves. Plants plan ahead and store food for when the going gets tough. Vegetables like harvested squashes or onions make great use of their food reserves—i.e. carbohydrates—without freaking out. In turn, they enjoy long shelf-lives.

Arugula, on the other hand, can’t handle the stress and gobbles up its stored energy twice as fast as other leafy greens. This type of consumption is known as the respiration rate and arugula is a respiration speed demon. By the time greens like chard, lettuce, or spinach in your fridge have depleted half their reserves, arugula is a wilted, yellow mess nobody wants to eat. Baby arugula goes bad even faster—the younger the arugula, the faster it respires. How, then, are we even able to eat fresh arugula if we don’t grow it ourselves? Human intervention helps!

take a chill pill

If you grow your own arugula you can cut what you need and eat it right away without worrying about shelf life. If you lack basic gardening skills like me and have a hard time growing vegetables but live in arugula-growing states like California, Iowa, or Arizona, you can buy fresh leaves a day or two after they’re picked. If arugula isn’t grown near you, it is going to have to travel to a distribution center, store, and finally, your fridge. Throughout that journey, cold temperatures are key to a longer shelf life.

Refrigeration prevents arugula from freaking out: much like a polar bear in winter hibernation, low temperatures after harvesting temper arugula’s appetite for its own reserves. And the colder, the better. At a chilly 32F, arugula’s respiration rate is five times slower than at 50F. The slower arugula consumes itself, the longer it will last. To optimize for the longest shelf life possible—about two weeks—arugula should always be kept at almost freezing temperatures, whether in a truck during transport or in the coldest compartment in you fridge, usually a crisper drawer at the bottom.

Cold temperatures slow down respiration. But what about transpiration? The higher the humidity, the slower arugula will lose its water. Arugula doesn’t want to be kept sitting in water, though, just in an environment that resembles a cold, foggy Bay Area morning. One way to create that fog is in refrigerated trucks that can control humidity to keep arugula sleepy and humid enough from the farm to its destination. Once at the market, arugula can be kept in refrigerated bulk bins or on refrigerated shelves with overhead sprinklers.

plastic fantastic

If shelves with sprinklers and humidity-controlled trucks are not an option, our food distribution system has come up with a simple way to package arugula: just throw it in polypropylene, aka plastic, containers. Unlike paper, plastic is excellent at retaining moisture and minimizes water loss in leafy greens, helping arugula go that extra mile. When it comes to extending shelf life, arugula sold without packaging doesn’t stand a chance against arugula packaged in plastic. Extending shelf life is important for grocery stores: the springy, triple-washed, ready-to-eat arugula in its protective plastic box or bag is convenient, attracts buyers, and theoretically reduces food waste because the greens don’t go bad as quickly.

But packaging five ounces of arugula in a plastic container has major downsides. We use containers to control transpiration and respiration, slowing down arugula’s need for speed. We’ve built a food system in which arugula grown in Salinas, California can show up fresh in a grocery store 1,800 miles away in Kansas City, Missouri. It’s an admirable scientific and logistical feat. But many variables have to align just right for that 1800-mile arugula to show up fresh and entice shoppers. A day or two in transportation delays results in hundreds of pounds of discarded food.

Salinas, California, grows 70% of the salad greens in the United States, and the local dump often receives 15-foot piles of perfectly edible spring mixes, which often contain arugula, spinach, lettuce, and other greens. Why? Taylor Farms, a large salad processor in Salinas Valley, packages 14-day shelf life arugula in plastic containers. As soon as it is harvested and packaged, that arugula has to make it out the door so it can reach long-distance markets. If, for whatever reason, that packaged arugula doesn’t ship in two or three days, some of it will go from farm to packager to dump with ten days remaining until its sell-by date. If that Salinas arugula still has ten more days until it wilts, there simply is not enough time to transport it to the receiving grocery stores in faraway cities. Those grocery stores need ample time to sell fresh arugula. If they only have five days to sell a shipment, it’s not worth accepting the order. Unfortunately, the Salinas packager has no choice but to discard the edible arugula. Excess salad greens are donated when possible, but supply and food-bank demand don’t always match. And the fact that arugula and other salad mixes are in plastic means they can’t be composted at a large scale. Someone would need to manually sort the plastic from the vegetable and manual sorting is expensive—it’s cheaper just to dump it all.

Even when fresh arugula makes it into our kitchens, its containers end up at the dump anyway. Often, the plastic that protects arugula and extends its shelf life is single use. After eating packaged arugula, that polypropylene container becomes another piece of trash that will break down into tiny pieces and end up in our oceans, in our fish, honey, or potable water, and back inside our guts… or sit in a landfill for 20 years at best before breaking down. This is a cycle with no clear end in sight, and our appetite for plastic is as strong as ever—the United States generates 17% of the world’s plastic waste.

But what about recyclable arugula packaging?  Wouldn’t it have multiple, if not infinite, uses? The packaging from brands like Plenty and Organic Girl cocoon arugula in 100% recyclable and made from 100% recycled materials.

In theory, those containers should go in the recycle bin, be taken to a recycling facility, and be repurposed into another useful object. In reality, that promise falls short—recycling works well with aluminum, for example, but we do not have the infrastructure, policy, and technology to actually recycle the majority of plastics. To understand why, I asked Dr. Usnavy “Matt” Kade, a polymer chemist who loves to nerd out on plastics. Recycling facilities in the U.S. recycle less than 9% of plastics. At best, plastics are downcycled into fleece or carpets, actual plastic recycling is not too common. One main reason is different plastics don’t mix well. For example, as Dr. Kade explains, if you get a little polyethylene mixed into polypropylene, the end result will be weak and useless. Worse, there are three different types of polypropylene that can’t be mixed together during recycling, but aren’t labeled and therefore can’t be separated from each other.

Recycling is also hyper-local: while San Francisco accepts #5 polypropylene, Oakland only accepts #1 PET and #2 HDPE plastics. In Berkeley, they don’t even go by numbers, they simply accept rigid plastic regardless of the number or color. In Oregon, none of the polypropylene arugula containers can be recycled. And while it’s great that we have plastic containers made from 100% recycled materials, those containers cannot be recycled again. At the end of the day, it’s cheaper to make packaging from virgin plastic.

Best friends: shaved parmesan cheese and Riverdog arugula grown in Guinda, delivered in a brown paper bag in a CSA box.

tender, loving care

Online grocery stores like Zero and Good Eggs both sell bunched arugula without any packaging and neighborhood brick-and-mortar stores in the Bay Area like Monterey Market and Berkeley Bowl also sell it by the bunch or in bulk. Arugula sold this way won’t last as long on store shelves or in our fridges, but we can help it out along the way. A simple water soak in the fridge for 30 minutes up to a couple of hours will bring wilted arugula back to life.

Soaking arugula allows cells to absorb new water, filling the vacuoles back up and restoring the structural support lost in transit. A cold water soak is a nice bonus: cold water stiffens cell walls so that when we munch on the leaves, they feel crunchier. This works well with most vegetables, and there’s a surprisingly entertaining nerdy time lapse of a super sad lettuce leaf soaked to sturdy greatness over the course of hours that you can watch in a few seconds. How exactly water gets into cells wasn’t known until recently and those details, which you can watch here, earned scientists the Nobel Prize. If arugula changes color, gets slimy, or grows mold, then by all means, please compost it! There’s no amount of soaking that will help. But if your ‘rug is simply deflated a bit, a cold soak will provide a refreshing opportunity for the leaves to fill up again. Plastic containers do a lot of this work for us, but if loose or bunched arugula are available, remember that soaking is always an option that can help reduce food and plastic waste.

arugula every which way

With all this fresh arugula around, what do you do with it? If intense peppery and bitter flavors don’t sit well with you, avoid the large, mature arugula and try to eat the baby variety instead—and eat it ASAP. During summer, arugula pungency will intensify compared to the cooler winter months. Microgreen arugula, though more expensive than the baby one, is a fun taco or sandwich topping. Arugula is great in salads, and an arugula, shaved parmesan, fresh ground pepper, lemon, and olive oil salad is a classic. Another popular use for arugula is as a pizza topping added fresh after the oven. Arugula plays nice with other greens and is often mixed in a mesclun—an Alice Waters favorite described in her new book—with dandelion, chevril, frisée, and young lettuces to make salads. Yotam Ottolenghi mixes dates, sheep’s cheese, basil, and almonds in a sweet, savory dish with pomegranate molasses that I can’t wait to try. Pastas and arugula also work: Kenji Lopez-Alt whips up a quick creamy pasta with three cups of arugula and some prosciutto and peas (see The Food Lab, page 713). An arugula walnut pesto can be a wonderful alternative if you’re out of basil or need to give the wallet a break—pine nuts in the traditional Genovese pesto are expensive! You can make several cups of arugula pesto—the leftovers freeze well (just add a thin layer of oil on top) so you can have green sauce on the ready, it goes on anything! Another great green sauce is the arugula version of a tangy salsa verde with parsley, capers, lemon, garlic, and olive oil. This one works well as a sandwich spread, drizzled over shrimp, portobello mushrooms, or really just about anything. Finally, arugula tossed with a little lemon, olive oil, salt, and pepper makes a great bed for morning poached or fried eggs. If you fancy a cocktail to go along with your meal, maybe try a Backbar arugula gimlet to add a spicy kick to the gin classic.

No matter how you end up eating it, to get the most flavor and crunch out of arugula, it’s good to eat it the day or the day after you buy it. Whether in a container or not, arugula transpires and respires quickly, so place it in a visible spot in your fridge to keep it in sight and in mind. Remember that even if that bunch of arugula arrives wilted from your online order or looks a little sad on the grocery store shelf, not all is lost. Give it a second chance with a proper cool soak and enjoy a livelier and sturdier super green.

“rocket” science

We’ve gone to remarkable lengths to extend the life of a plant that naturally doesn’t want to last long after harvesting. Through our knowledge of plant biology, chemistry, and material science—polymer chemistry in particular—we have forced arugula to bend to our will for the sake of freshness in spite of distance. Our insistence on control through plastic comes at a high price, especially since our plastic waste keeps growing and we continue to drive fresh food straight to the landfill.

If we relinquish some control and adjust our expectations, we could transform our food logistics system in a different way. What if we decentralized agriculture by growing arugula in many states instead of (basically) just California, thereby reducing distribution distances from thousands to hundreds of miles? Unlike other finicky vegetables, arugula is a low maintenance crop that’s relatively easy to grow. It might be more feasible, then, to curb our reliance on plastic containers. This approach doesn’t require rocket science (unless you’re British!). It’s simply a way in which we could adapt to arugula. A way—though not easy by any means—to work with nature. Arugula’s unique physiochemical properties have already transformed our food system once. If we rethink our relationship with this humble leafy green, we could transform it again—for the better.

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Andrea Castillo is a food nerd who always wants to know the what’s, how’s, when’s, and why’s of the food she eats.