Processed: Food Science and the Modern Meal

Before 1920 lettuce was eaten as a seasonal vegetable in most parts of the United States. At that time food producers began using infrastructure built to transport sugar beets to ship iceberg lettuce year round. While largely tasteless, iceberg lettuce could better withstand refrigeration and the bumps and bruises of travel. (Library of Congress)

Before 1920 lettuce was eaten as a seasonal vegetable in most parts of the United States. At that time food producers began using infrastructure built to transport sugar beets to ship iceberg lettuce year round. While largely tasteless, iceberg lettuce could better withstand refrigeration and the bumps and bruises of travel. (Library of Congress)

Almost Garden Fresh

Americans may occasionally wax philosophical about the flavorful delights of garden-ripe produce, but as a population we’re more willing to sacrifice taste and aroma for year-round access to fresh fruits and vegetables.

The now century-old industrialization of produce, particularly fresh lettuce and tomatoes, has led to the growing of varieties that can survive long-distance transport. While our produce looks good with jetlag, it often comes at the cost of flavor and aroma. But there is some good news: in some cases a new understanding of the biochemistry of ripening and decay may help the agriculture industry give us the best of both worlds.

During the late 1910s and early 1920s iceberg lettuce went from near obscurity to one of America’s most eaten fresh vegetables. It was the only variety of lettuce that could survive a train trip from California fields to East Coast markets without turning into a sodden mess of goop, explains food historian Petrick. Before World War I most lettuce consumed on the East Coast was leaf or butter lettuce, and it was eaten only during the spring and summer growing seasons, she says.

Petrick found that in the later part of the 1910s California farmers began to capitalize on their year-round growing season, excellent rail infrastructure (built to transport sugar beets cross-country), and better train-car refrigeration. Iceberg lettuce was the chosen food not for its flavor—it has little—but for its long shelf life and resiliency. Iceberg’s ideal storage temperature was just a degree or so above freezing, temperatures that would make other lettuces limp, Petrick says. Initially crushed ice was used to keep the lettuce cool, but in the 1950s vacuum-cooling technology originally developed during World War II reduced spoilage across long distances.

The changeover was quick. In 1917, 50% more butter lettuce was being shipped throughout the United States than iceberg. By 1925 four times more iceberg lettuce was shipped than butter lettuce, Petrick has discovered. “Instead of having truly high-quality, fresh-from-the-field lettuce, Americans ate lettuce that was ‘good enough’ to put on the table every day,” she says.

As refrigerators became commonplace in the late 1920s and early 1930s, the food industry, led by entrepreneur Clarence Birdseye, began to experiment with freezing rather than canning fresh fish and produce. It wasn’t a roaring success at first, notes the food historian Levenstein. Both the frozen produce and the wax paper that wrapped it would melt into mush. The wax paper was eventually substituted for newly available plastic, and Birdseye rebranded frozen food as “frosted food,” which didn’t melt but “defrosted.” It was a clever marketing trick, says Levenstein, because it made everything from frozen peas to berries sound more appealing. Birdseye also developed flash freezing in the 1920s, which preserves food texture. In slow freezing ice crystals form in cell walls and break them down, making the thawed food mushy.

Another strategy widely used today is to delay ripening itself: pick produce early, transport it to market, ignite ripening, and sell. Unripe produce is usually hardier and can better withstand the jostling and other insults that take place during global transport, remarks plant biochemist Harry Klee. In the best-case scenario ripening can be timed to coincide with the produce’s appearance on store shelves. “But all this comes at the cost of flavor, color, and texture,” he adds.

Since ripening is a fruit’s equivalent of hitting puberty, controlling the process is a matter of controlling a plant’s ripening hormones and the genes these hormones activate. In the case of the common supermarket tomato, breeders have selected for a plant with a genetic mutation that interferes with the softening that occurs during ripening, says Klee. Unfortunately the same mutation prevents the tomato from producing the flavor compounds that are part of the ripening. No matter how long you leave a standard supermarket tomato in the sun, it will never achieve the flavor and texture of an heirloom variety.

Although this type of tomato has been on supermarket shelves for decades, not until 2012 did a team of researchers at Cornell University figure out the reason for its flavor failure: in short, a mutation in a gene called SlGLK2. The gene’s corresponding and dysfunctional protein won’t activate the production of chloroplasts, which harness light energy to produce sugar. Chloroplasts are also where many of the tomato’s characteristic flavor and odor compounds are produced.