Ripe

We all know when a gym bag is ripe, but what about the fruits and vegetables in your garden?

According to the dictionary, ripe refers to fruit or grain that has developed to the point of being ready to harvest and eat. Okay, so that rules out all those leafy vegetables, such as chard and spinach, that we can eat whenever we feel like it. That definition also pushes herbs to the side. With grain being the fruit of a cereal grain, it looks like ripeness only applies to fruit. But what (or who) decides when a fruit is ripe or not?

An unripe fruit

If you have ever tried eating an unripe fruit, you know that the experience can be less than satisfying. Starchy, bitter, and tough, unripe fruits are very unlike the ripe versions of themselves. Some fruits, such as lychee and Chinese lantern berry, can be downright dangerous to eat unripe. Unripe apples and plums are safe, but eat too many and you’re in for a stomach ache. And, if you happen to bite into an unripe persimmons, be prepared to feel like the inside of your mouth caved in on itself. So how do these hard, green, astringent fruits turn into the soft, juicy sweetness we love?

Ripe and unripe Early Girl tomatoes (Mika Masuzaki) CC BY 3.0

It’s all about ethylene

The lowly ethylene molecule is responsible for many changes within a plant. Ethylene is used by plants in respiration and to inhibit the movement of auxins, a plant growth hormone. By manipulating auxin levels, plants use ethylene to stimulate seed germination and adventitious root growth. It is also used to bend the plant toward the sun (epinasty). This ripening, or aging, hormone also triggers abscission (leaf and ripe fruit drop), chlorophyll destruction, flower drop, and all the signs of senescence (deterioration related to aging).

The physics of ripening

Fruit is food for seeds and seed spreaders. When a fruit falls to the ground, it provides easy access to important nutrients to the seed or seeds contained in that fruit. It also attracts animals that may help the plant disperse its seeds over a wider range. There’s no sense in attracting fruit eaters if the seed isn’t ready. Just as the seed(s) approach maturity, a series of chemical changes take place within a fruit. That’s when ripening kicks in. We all know that, as a fruit ripens, it becomes sweeter and softer. Generally, fruit becomes less green and more colorful as it ripens, too. This is because enzymes are breaking down the chlorophyll. [One study found that birds of different continents prefer different colors of ripe fruit.] This sweetening and softening is the result of certain enzymes breaking starch down into various sugars, such as fructose, glucose, and sucrose. [Any time you see a word ending in -ose, it’s a sugar.]

Some fruits stop ripening as soon as they leave the parent plant, while others continue ripening. Those that continue ripening are called climacteric. Common climacteric fruits include bananas, apples, mangoes, melons, and apricots. These fruits are frequently stored before appearing on grocery store shelves. Non-climacteric fruits, such as grapes, citrus, and strawberries must be harvested when ripe.

Unripe and ripe strawberries

Natural vs. artificial ripening

Fruit can be ripened artificially, or it can be allowed to ripen naturally. Naturally ripened fruit takes longer and is less well suited to storage and shipping. It also has higher sugar levels, more complex flavor, and better texture. Fruits are artificially ripened using ethylene and acetylene gases in pressurized, temperature-controlled containers.. These methods are used by most large-scale fruit sellers. These fruits are picked green to allow for shipping and storage.

​But, before anyone starts bashing Big Agriculture for the problems they create, we have to give them credit for the Big Problem they have helped prevent: starvation on a very large scale. Figuring out how, and investing the necessary capital, to make such large quantities of food available year round is no small task, and I am grateful that they do. It is estimated that as much as 80% of all fruits are ripened artificially. [Check out thiat link and give it a read]. Unfortunately, as you saw in the linked article, too many ripening facilities use chemicals, such as calcium carbide, that are known to be unsafe. [I just learned that a glove is being developed that can tell if a fruit is ripe or not!]

Even if a fruit is artificially ripened safely, it will still lack the flavor found in a naturally ripened piece of fruit. This is because artificially ripened fruits may look ripe, but they may not actually be ripe. As a fruit ripens, sugar levels increase. You can see a detailed study on sugar levels and ripeness here. Reaching that state of perfect ripeness takes time. So, I grow my own and urge you to do the same. Your sun warmed, fully ripened tomatoes, cucumbers, apples, apricots, and other home grown fruits have the time they need to reach their peak of flavor, sweetness, and texture.

Some home canners claim that underripe and overripe fruits will float and just right fruits will sink, but this isn’t always true. Floating is related to density, so that rule is very species specific. Generally, smell is the best indicator of ripeness we have, unless it’s a cranberry.

Ripe cranberries bounce.