Welcome to Savor the Science! In each Savor the Science, RENDER’s resident chemist, Claire Lower, will explore culinary questions through a scientific lens, perfecting recipes and demystifying techniques. Theories and reactions will be discussed and experiments will be performed; it’s like your high school chemistry class, only edible. Twice a month, Claire will take a scientific concept (such as the acid-base reactions in baking, macerating, or Maillard browning), explain it in a way that would make Bill Nye proud (hopefully), and then provide an edible experiment which allows you to demonstrate your new scientific food knowledge.
It’s science you can eat!
I would never refer to myself as a “botanist.” I can barely tell a rose from a begonia. I can only recognize an orange tree if it has actual oranges growing on it, and sometimes I’m not even that great at correctly identifying fruits. Recently, I was visiting my parents and I noticed a small, shrub-like tree with yellow, apple-esque fruits hanging from it.
I thought it was an apple at first, but my stepmom was quick to inform me that it was a quince. This was a happy coincidence (quincidence?) because this fruit is not only difficult to find in the U.S. (it’s not farmed here commercially), but also extremely interesting due to the chemical changes it goes through during cooking.
Usually, an unhappy side effect of cooking fruits and vegetables (especially vegetables) is that the heat alters the molecules responsible for color, making them appear dull and drab. But in the case of the quince, heat transforms these babies from astringent, colorless little rocks into ruby-colored jewels of soft, sweet fruit-flesh, perfect for pairing with salty meats, strong cheeses, oatmeal, roasted fowl, and the list goes on.
There are three factors that make a quince a quince [Editor’s Note: shall we say quincessential? har. har. ]: a high level of pectin, the presence of tannins, and anthocyanin.
Pectin is a polysaccharide (a long carbohydrate) contained in the cell walls of plants. It can be extracted from fruits (usually citrus) and is used as a gelling agent for jams and jellies or as a stabilizing agent for juices, medicines, and confections.
In plants of the non-woody variety, pectin helps them grow long and strong by “cementing” the walls of cells together. In fruit, the pectin is broken down by enzymes during ripening, allowing the flesh to soften and become suitable for mashing up with your chops.
The high levels of pectin in quinces means they lend themselves wonderfully to jams and jellies, but also accounts for the hard, gritty texture of the raw quince; no amount of ripening will make these suckers soft enough to chew. (Though there are some varieties that can be eaten out of hand, such as the “Kuganskaya,” but you won’t find those in the U.S). Cooking weakens the cell walls of the fruit by gradually breaking the pectin into smaller and smaller chains. If you cook them long enough, almost all of the pectin in the quince will be dissolved, and the quince flesh will disintegrate (McGee 1984).
You know when you take a swig of a dry red wine and your tongue feels drier and your teeth feel stickier? That feeling is due to tannins, and their presence in quinces has a similar effect when you try and bite into a raw one.
Tannins are a bitter plant compound that bonds to proteins. Once in your mouth, they bind with the proteins in your saliva, clumping them together and preventing them from performing their usual lubricating duties. This is what gives quinces their “astringent” quality.
Heating the tannins destroys them, eliminating the quince’s astringency and leaving behind a delicate, fragrant flavor.
When people think of molecules responsible for the colors in fruits and vegetables, chlorophyll often comes to mind, maybe beta carotene. Rarely do folks think of anthocyanin, the molecule responsible for the delightful reds, blues, and purples observed in some fruits.
When you slice into a quince, you will notice the coloring is not red or blue or purple, but rather white. (As mentioned above, it’s also very hard, so take care when slicing). The anthocyanin in the quince is all bound up in tannins, only to be released when cooked.
Because anthocyanin is water soluble, the cooking liquid will turn red along with the fruit giving you a beautiful, tart, and fragrant syrup.
Though there’s a lot going on at the molecular level, there’s very little you have to do on the macro. A little gentle poaching is all that’s necessary to transform quinces from their aggressive raw state into supple and sweet accompaniments for cheeses, baked good, or ice cream.
So, let’s transform some quinces!
Poached Lemon-Ginger Quinces
You will need:
About two pounds of quinces, barely ripe (should be slightly green still)
1 cup of sugar
The peel of half a lemon (removed with a vegetable peeler so you don’t get any of the white pith)
2 inches of ginger, peeled and cut into coins
Peel, quarter, and core the quinces. My quinces were quite small, so I didn’t have those large, beautiful slices you see on so many cooking blogs. Once they are all chopped and cored, place them in a bowl of water with lemon juice squeezed in, to prevent browning.
Add the remaining ingredients to a quart of water and bring to a boil. Add quinces, return to a boil and then reduce to the barest of simmers. Simmer for about 45 minutes, until quinces are soft and pink. Pour into a jar or similar container and let cool. Poached quinces can be stored in their liquid for a week.
Pro-tip: The liquid itself is delightful. Try it mixed into a cocktail or soda water.
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Harold McGee. 1984. On Food and Cooking: The Science and Lore of the Kitchen. (New York: Scribner), 283-284.