Candy carrots and turnip treats: why some veggies are sweeter in winter
What do winter tomatoes and summer carrots share in common? They’re boring and starchy because they’ve been grown in the wrong seasons. Frost-kissed carrots, on the other hand, are incredibly sweet and satisfying. Why the difference? You can divine the answer in a bag of potato chips.
Have you ever found a brown potato chip? This occurs before the chip ever makes it to the bag, often due to a process called “chill sweetening.” Potato tubers are still alive after harvest – you know this if you’ve had them sprout in your pantry or turn green, accumulating bitter and toxic saponins. Store potatoes in temperatures that are too cold, however, and they’ll start converting their starches to sugars. These simple sugars brown during frying, producing unattractive chips that consumers don’t like. Although you may like the sound of a sweeter potato, it can be a big problem for potato farmers, as entire harvests of potatoes that don’t “chip” well can be rejected by the food processor. What’s more, remember that potatoes are a warm-season crop; any meager sugar conversion is offset by the presence of other substances that react with the simple sugars when cooked to form bitter (and even carcinogenic) substances like acrylamide.
We may prefer starchy potato tubers, but root crops should be sweet and crisp. We want chill-sweetening to occur in root crops, as well as brassicas and greens, as the shift from carbohydrate stores to simple sugars is desirable for these plants. I like to think of it is as Nature’s antifreeze. The accumulation of simple sugars helps protect the plant tissues from freeze damage – although it isn’t everything that plants need to tolerate the cold, it sure is my favorite part! Plants also begin accumulating special freeze-resistance proteins (called “antifreeze proteins” by scientists) and alter the composition of their cellular membranes to withstand freeze stress. All of these changes take some time, which is why even cold-tolerant plants can be injured if a shift in temperature occurs too quickly.
How much difference does the right temperature make? A colleague of mine conducted rutabaga research for several years (not for food, but as a potential biofuel). During the first few years of the study, his research group grew increasingly frustrated that their plants never approached the sugar content published in the rutabaga literature. Their plants were apparently healthy and happy, growing incredibly tall, but the roots, although large and busting out of their pots, remained woody. A chance conversation with a farmer revealed their problem – they had been growing the rutabaga in a hot greenhouse, rather than out in the cold. Once they switched to cold growing conditions, their rutabagas sweetened right up.
Don’t care for turnips, beets, broccoli, or rutabaga? Perhaps you haven’t tried them “in-season” from a winter garden. Imagine if all you ever knew about tomatoes was what you had tried from a winter grocery store. Missing out on chill-sweetened root crops would be a similar travesty.
As you plan your summer garden, adjust your planting dates for roots crops so that they mature in fall and winter. In my plant hardiness zone (6b), I plant my root crops over the Labor Day weekend, then protect them from later hard freezes by covering with low tunnels or mulch. With a little planning, you can harvest sweets from your garden through all four seasons, looking forward to the harvest of that first frost-kissed carrot just as much as your sun-warmed tomatoes.
Additional Winter Gardening Resources:
These books are in my personal library, and I highly recommend them (these affiliate links cost nothing extra to you, but generate advertising fees that help me support this blog):
What could you be growing this winter? Check out this extensive list: my Winter Vegetable Planting Guide. And for more winter gardening resources from me, including how to build an inexpensive low tunnel, click the winter gardening tab above.