Hachiya persimmons, ripening

Jeanne discusses the biology behind the strange winter beauty of persimmon trees and demystifies why eating one before its time is an unpleasant experience.

The holiday seasons of my adult life increasingly include persimmons.  The ‘hachiya’ persimmons on my mother-in-law’s tree in California ripen around Christmas, beginning a conversation about what to do with them, and when they start showing up in the grocery store in late fall, I’m invariably drawn to the plump orange fruits with their handsome green calyxes.  I’ve now learned that persimmons, especially dried, are an important part of many new year celebrations throughout Asia, where there are thousands of persimmon varieties, but I only became acquainted with them when I moved from Denver to go to college in the Bay Area, where some of the Asian varieties are grown.  The bright orange plum-to-apple-sized persimmon fruits stay on the tree until well after the leaves drop in the autumn.  I paid little attention to the persimmon trees on campus—tall specimens of the ‘hachiya’ variety of Asian Diospyros kaki—until the leaves fell to reveal the scraggly branches laden with the orange orbs.

Japanese persimmon with fruit, National Arboretum

The sight startled and fascinated me, and I still find it exciting but a little unsettling.  The trees in winter are certainly beautiful and somewhat seasonally festive, but definitely foreign to me.  Part of their enigma for me might arise from the mystery of why a tree would leave its fruit on the tree past leaf drop.  This doesn’t seem to be particularly well researched.  It’s not necessarily a bad idea if the cold fruits can still mature their seed, and the strategy could be a great way to avoid some warm-season pests and pathogens, but I haven’t found any data supporting any particular hypothesis on the subject, and it bugs me.

Cut fuyu persimmon, revealing empty carpels

Another aspect of persimmon life history that intrigues me is their facultative parthenocarpy—part-time seedlessness.  Persimmons may occasionally set seeds if the wind or an insect pollinates their flowers, and some varieties produce sweeter, more flavorful fruit if the flowers were pollinated, but many don’t require pollination in order to make fruit.  You’ll see this if you cut a commercial persimmon in half cross-wise.  You’ll see a star pattern of empty carpels where the seeds would have grown.  Many plants produce some seedless fruits.  In wild parsnip, the strategy has been shown to be an effective strategy to prevent seed loss to herbivores, which prefer the seedless fruits (Zangerl et al. 1991).  Other researchers hypothesize that parthenocarpy might help keep fruit dispersing animals fed and in the region even if pollination fails in any given year.  Whether both or either of these functions of parthenocarpy explain its persistence in persimmon is undemonstrated.

wild persimmon seeds

Seeds are more common in wild persimmon fruits than in commercial varieties.  We now live in Maryland within range of the only persimmon species native to the United States (Diospyros virginiana).  My daughter and I have gone on a few walks this fall explicitly to find the fruiting wild trees.

wild persimmon tree with fruit

ripe, post-frost wild persimmon fruit

My illustrious blog co-author Katherine has fond memories of harvesting the sweet wild persimmons in Indiana and related to me an interesting story about persimmon folklore:  “There is an old tale about persimmon seeds foretelling the winter weather.  If you cut the seeds lengthwise and see a fork, there will be much snow.  A knife points to cold and a spoon points to mild weather.  The utensils are just the embryo, and the shape depends on your plane of section.  It clearly doesn’t work, but the legend persists.”

When I got my hands on those first hachiyas, the timely advice of a friend spared me the unpleasant experience of learning the hard way that most persimmon varieties are inedibly astringent before they are either completely ripe or dried.  We had to set them out in the windowsill until they were quite ripe.  Perfectly ripe hachiyas become translucent and jelly-like, and their flesh can be gently sliced and dried or easily spooned out of the skin and eaten as is, whipped with lemon juice in the blender for a refreshing, thick fruit mousse, or incorporated into puddings, sorbets, or soups.  Harold McGee suggests making a two-layered persimmon pudding, one layer made with baking soda and the other with baking powder.  The former produces an alkaline batter that turns the cooked pudding a rich dark brown via browning chemical reactions and mellows the fruit flavor, whereas the former preserves the honey-sweet but mild, pumpkin-like persimmon flavor and produces a pale golden pudding.

Fuyu persimmons

Other persimmon varieties, including fuyu or jiro, are non-astringent and can be safely consumed when crisp but are more delicious when allowed to soften and sweeten a bit, although they will never become as jelly-like as the astringent varieties.  The non-astringent varieties can be eaten like an apple or peeled and sliced into salads or fresh chutneys or salsas.  Slicing fuyus into salads is our favorite way to incorporate persimmons into our fall and winter menus.

Fuyu slices in salad with watercress and shaved white turnip

Most of the both astringent and non-astringent persimmon varieties grown in the United States are cultivars developed in China and Japan of a single species native to northern China with peach-sized fruit, Diospyros kaki, which itself is just one of the 450-500 species in the large genus Diospyros, in the family Ebenaceae (asterid order Ericales—please see our food tree for phylogenetic context).  The family Ebenaceae gets its name from the other economically important product of the genus Diospyros:  ebony, the extraordinarily dark and dense wood.  Only a few species have the dark or streaked heartwood harvested for ebony or calamander wood, respectively, and those tend not to have particularly desirable fruit.  All species in the genus, however, have especially hard wood and make excellent timber.

The high fruit tannin content is to blame for the astringency.  Tannins deter herbivores from eating the fruit until the seeds, if they exist, are mature.  Tannins are a large chemical group of phenolic compounds that function by binding protein.  They cause the uncomfortable dry-mouth, furry-tongue feeling that comes with biting an unripe persimmon (or unripe banana or extraordinarily tannic wine or black tea) by binding the proteins in your saliva to the proteins in your tongue.  Large specialized cells throughout the fruit store the tannins.  Harold McGee suggests an activity you can do the kitchen yourself to see these tannin storage cells:  place a pinch of baking soda on a small amount of ripe persimmon pulp.  In a few hours thousands of little black rods will appear on the surface of the pulp, where the baking soda oxidized the tannin masses and caused them to absorb enough light to be visible.  As the fruit ripens, acetaldehyde produced during ripening causes the tannins to bind to each other, consolidating them into unreactive masses inside their storage cells, removing the astringency.  The non-astringent varieties still have tannins, but the tannin cells are much smaller and have less tannin.  This condition is caused by a recessive genetic mutation that interrupts tannin cell development early (Kanzaki et al. 2001).

Japanese persimmon, still very much astringent

Freezing, drying, mechanically whipping the fruit in a blender, and depriving the fruits of oxygen in a bag in a warm place for a few days are other mechanisms for modifying fruit cell metabolism and/or breaking the cell walls, so that the tannins leak out and bind to other proteins in the fruit and thereby become inactive.  Katherine remembers that the wild persimmons in Indiana were traditionally harvested after the first frost, to ensure loss of astringency through both ripening and freezing.  This tannin leaking-and-binding also thickens the fruit pulp and can turn ripe persimmon fruit into a lovely fruit mousse or sorbet, no eggs or cream or gelatin needed.  But this thickening can also hurt you.  If you eat too much ripe persimmon on an empty stomach, the thickening will happen so quickly and vigorously inside your stomach that it can bind the persimmon tissue into an indigestible mass—a bezoar—that cannot pass into your intestine and can cause digestive havoc and will require surgery.  Seriously.  So, persimmons in moderation and with other food, please.  And happy holidays!

References

Kanzaki, S, K. Yonemori, and A. Sugiura. 2001. Identification of molecular markers linked to the trait of natural astringency loss of Japanese persimmon (Diospyros kaki) fruit. J. Amer. Soc. Hort. Sci. 126: 51-55.

McGee, H. 1990. The Curious Cook. Collier Books, New York.

Zangerl, AR, JK Nitao, and MR Berenbaum. 1991. Parthenocarpic fruits in wild parsnip: decoy defence against a specialist herbivore. Evolutionary Ecology 5: 136–45.