I guess I always knew that some fruit ripened more satisfactorily after it was harvested than other fruit, but until fairly recently it didn’t occur to me that this means there is some fruit it makes absolutely no sense to buy unripe. The path fruit takes to ripeness is actually quite interesting, as are the mechanisms used to artificially induce “ripeness” along the way.
Obviously once a fruit leaves the tree it is cut off from its supply of nutrients and has to rely only on what it already contains if it’s going to continue to mature. However some fruits, climacteric fruits, are able to use these reserves to ripen themselves in a “climax” of ripening activity, while other fruits, non-climacteric ones, can only ripen at a steady rate while connected to their source of nutrients and once they are picked just begin to rot. Climacteric may sound like kind of a naughty word to use for fruit, but really it’s a useful distinction to be able to pick out in the supermarket.
Non-climacteric fruits include blackberries, raspberries, strawberries, cherries, grapes, pineapples, citrus in general, and watermelons. This means that whatever level of sweetness and ripeness was present in these fruits when they were picked is what you are going to get when you eat them. They may continue to redden and soften, like strawberries, but they aren’t getting sweeter: they are rotting.
Citrus obviously has a longer shelf life than many of these other fruits, but this is in part due to the fact that it’s generally harvested completely unripe and then (in the case of basically every orange you’ve ever bought in the supermarket in the last several decades) gassed with ethylene (the internal ripening hormone of fruit) to turn it from green to orange. Oranges picked ripe have thin smooth skin, not the thick skin with deep pores that was green at the time of picking and is common in those tasteless, uniformly-orange supermarket oranges.
Climacteric fruits, which do continue to ripen after picking, can also be divided into two useful categories: those that continue to gain in color, texture and juiciness, but not sweetness and flavor, and those that continue to mature in all of these categories. The first type includes peaches, nectarines, plums, blueberries, apricots, and most melons. This means that while these fruits will look and feel like they are further ripening after harvest their flavor and sweetness isn’t really changing because they are not supplied with enough starch to turn to sugar. They won’t even ripen in color, texture, and juice unless they are picked mature enough, which lots of fruits (such as peaches bred to develop a pretty blush long before they are ripe) often are not. To be delicious these fruits really need to be picked close to ripeness, not picked hard and green so they can be shipped, stored, and gassed with ethylene to induce ripening (which for these fruits will mean ripening in color and texture but not sweetness, and the more immature they were picked the less sweet they will ever be).
However there are also climacteric fruits which develop in all ways after harvest, including in sweetness and flavor. These include apples, kiwis, mangoes, pears, bananas and sapotes. (If you’ve never had a sapote they are amazing, be on the look out.) These fruits are clearly the best to buy unripe as they will continue to develop and sweeten at home; however most bananas, apples, kiwis, and pears, (in particular all those purchased out of season), have still been placed in cold storage to delay ripening and then gassed with ethylene to trigger ripening.
Bananas are the best post-harvest ripeners of all: they are totally fine to buy perfectly hard and green as they will continue to ripen and sweeten almost to exactly the same point they would have on the tree. Both apples and bananas even produce enough ethylene in their climacteric ripening to trigger other fruits to ripen (at least other climacteric fruits); this is why a ripe banana or apple in a paper bag or a fruit bowl will help hurry along the ripening of other fruit in the bag or bowl.
Being sprayed with ethylene to induce ripening is not necessarily bad for the fruit or bad for the consumer, after all this is the ripening hormone that fruit naturally produces. When you place fruit in a paper bag to ripen you are essentially doing what the fruit industry is doing: closing fruit in with ethylene to ripen it. Organic fruits are sprayed along with their non-organic counterparts. The downside of all this ethylene spraying is really the sacrifice of sweetness and flavor: fruit picked hard and young can be shipped far and arrive in pretty condition, it just won’t ever taste as good. Unless it’s a banana.
Thanks to the book The Man Who Ate Everythingfor initially informing me about climacteric fruit. This book is a fascinating (and very funny) collection of essays by Jeffrey Steingarten, food critic for Vogue.