Over the past few weeks, with autumn winding down and winter drawing near, we’ve been enjoying winter vegetables — carrots and potatoes, cabbage and Brussels sprouts, squashes of all sorts. Some of these squashes weren’t quite ripe when harvested, but after several weeks sitting on a warm, sunny windowsill, they ended up just as sweet and delectable as their earlier relatives. 

Who would have guessed? In my many years of gardening I’d always assumed that any green squash remaining on the vines when frost approached should be tossed on the compost with the spent vines. In the case of this year’s buttercup squash, large and very close to being ripe, tossing them would have meant no crop at all. Luckily I recalled a huge heap of orange pumpkins stacked at a roadside stand, many of which were only partly ripe when I first saw them. A couple of weeks later, they had all turned deep orange, so I assumed that squash would ripen off the vine as well. In the case of my squash, I cut them off the vine, leaving a couple of inches attached to the stem, wiped them clean to discourage any mold or rot, then set them in the sun on windowsills, where they looked like planned harvest decorations. Without sunlight, squash will remain green and unripened, so a sunny spot is essential. If a whole squash is unripe, it should be turned periodically so that it can ripen on all sides. If only one side is unripe, put that side toward the sun and it will do the job. 

After I told my daughter that the squash she was eating had finished its ripening inside, she said perhaps I should devote a column to discussing what other fruits and vegetables continue to ripen after harvest. We all know some of the answers, but there’s obviously room for error and misconception in the ripening vs. rotting scenario. 

First, a brief discussion of the ripening process, which is the way in which fruits attain their optimum flavor, quality, color, and textural properties. Ripening is basically just the conversion of starch to sugar. On the basis of their manner of ripening, fruits are classified as climacteric or non-climacteric. Climacteric fruits are defined as fruits that enter their climacteric phase after harvest; that is, they continue to ripen. During this ripening process the fruits emit ethylene and have an increased rate of respiration. Most fully ripe fruits are soft and delicate and can’t stand up to the time and trials of transport and repeated handling. So these fruits are harvested hard and green, but fully mature, and are ripened by commercial handlers who use small doses of ethylene to induce final ripening under controlled conditions of temperature and humidity. Non-climacteric fruits, once harvested, do not ripen further. They produce a very small amount of ethylene and do not respond to ethylene treatment. ?

So which fruits and vegetables do not continue to ripen after picking? Most berries, including blackberries, raspberries, blueberries and strawberries, fall into this group. But wait, you say: I’ve had berries that were only three-quarters red that colored up after a day or so. Yes, strawberries can become redder, but with that increase in color you will notice spots of discoloration appearing and even off-flavors developing, an indication that the added color is actually the start of decay, not the beginning of peak ripeness. Other fruits that do not ripen after picking include cherries, grapes, all citrus, watermelons, pineapples and pomegranates. There are also vegetables that do not ripen after harvest, among them summer squash, eggplants and cucumbers. 

While a watermelon will not continue to ripen after harvest, other melons, such as cantaloupes and honeydew, will. When a cantaloupe ripens and falls — or is picked — from its vine, it’s not dead but simply entering the final stage in its ripening process. As long as it remains intact, it will continue to grow juicier and more fragrant. This prepares it to break down quickly and fertilize its cargo of seeds, a process that begins when you finally cut into the melon.

Fruits that continue to ripen after harvest are picked once they have matured to their optimum size but are still not quite ripe. These fruits produce their own ethylene gas, which continues the ripening process. As mentioned, commercial growers still may use some ethylene gas to quicken the ripening process and enhance the color of the peel. Apples, apricots, bananas, kiwis, mangoes and plums will all ripen and continue to do so after they’ve been brought  into your home if left at room temperature. Tomatoes, as all Maine gardeners know, can be picked green ahead of a frost and will ripen slowly if packed away in boxes, where they too release their own ethylene gas. This year, a hot and dry one, saw most tomatoes fully ripening on the vine, but in past years we’ve had garden tomatoes emerge from their cardboard storage as late as mid-December ­­— still miles ahead of their supermarket cousins in flavor and texture.

While many fruits reach their peak on the branch or vine, there are exceptions. Pears, for example, need to be picked before ripening. If left on the tree, pears ripen from the inside out and by the time they seem to be at the ripe stage, they’re beyond it — mushy, with a mealy texture beneath the skin. To select a ripe pear to eat immediately, press a finger gently into the top of the pear just where the stem joins the fruit. If it just starts to give there, the fruit is ripe. Pears that are soft anywhere else are over-ripe. Just leaving firm pears at room temperature for a day or so will bring them to juicy perfection.

Avocados, like pears, ripen or soften only after they have been harvested, which is why you’ll find bins full of grenade-like fruits in the market. To speed up the avocado ripening process, the traditional placing of the fruit in a brown paper bag with an apple or banana for two to three days will make them guacamole-worthy. Placing them on a sunny windowsill also works well.

I’ve heard of an instant ripening technique, but not tried it. If you need a ripe avocado in a hurry, wrap the whole fruit in tinfoil and set it on a baking sheet in a 200°F oven for 10 minutes, or until the avocado is soft (depending on how hard it is, it could take up to an hour to soften). Remove it from the oven, then put your soft, ripe avocado into the refrigerator until it cools. Supposedly, as the avocado bakes in tinfoil, its ethylene gas surrounds it, speeding up the ripening process. Haven’t tried it, not sure I want to, but I’m putting it out there for those desperate for their breakfast avocado toast.