Kitchen Mysteries is a weekly exploration of oddities surrounding cooking and food. They could be recipes that fail when they shouldn't, conflicting advice from different sources, or just plain weirdness. If it happens in a kitchen, and you're not sure why, send a tweet to The Food Geek to find out what's happening.
BeenThere8That asks via twitter:
Now that spring has rolled through and summer has arrived, the farmer's markets, CSAs, and other purveyors of seasonal produce are overflowing with fruits. After watching a few too many delicious treats rot or mold away, action must be taken. A great action to take is to turn that fruit into jam.
The unfortunate fact is that, when you're trying to make a jam with traditional fruit pectin, you are limited in amount. Really, that's true with just about any thickening agent; there's going to be a limit to what you can conveniently combine together, but the jam limitations seem more constrained versus what people want to do than, say, making a gravy.
Pectin is found in the cell walls of plants, and it gives support to the cell walls. You can see in my article from issue 100 of Fine Cooking on leaves and lettuces that the cell walls tend to be stiff in plants, and pectin provides structure for that stiffness. When you cook down fruits, especially crisp ones with good structure to them, the pectin comes out.
Pectin, interestingly, doesn't really like hanging around other pectin molecules. Given the opportunity, pectin will go its own way, spending some quality alone time working on its novel, composing its symphony, or doing whatever it is that pectin does when it's not being pestered into forming long molecular chains that suspend water molecules in a thick gel.
The reason pectin likes to be alone is that it is electrically charged, and as all pectin have the same electrical charge, they push away against each other much as the same pole of a magnet will repel each other. Therefore, in order to turn the solitary pectin molecules into a water trapping cage, you have to do two things: first, you have to make sure that the pectin have no better place to be; second, you have to get them to want to spend time together.
To limit where the pectin can go, you need to reduce the amount of water that the pectin is swimming in. Your first impulse might be to just reduce down the liquid to a tiny amount, but you'll find that the sheer amount of pectin needed to make a tiny jar of jam would be prohibitive. I'm not sure what else it would do, but I'd imagine that the flavor wouldn't be all that great in a jam made that way. So we need another way to reduce the amount of water without drastically reducing the total volume of liquid. It sounds crazy, but there is a way.
As long-time readers know, sugar and water really like each other, and sugar will make sure that water does go hanging around with shady molecules like pectin whenever sugar is around. That's why jam recipes tend to be on the sweet side, because you have to have a certain concentration of sugar to water in order guarantee that the water won't sweep the pectin away and prevent it from forming strong molecular chains.
Candy makers know that, as you increase the concentration of sugar in water, the boiling point of the water rises. Unlike with your typical pasta water and salt, in which the water molecules vastly outnumber the salt molecules for anything that you're going to eat, the number of sugar molecules will compare quite nicely with the number of water molecules, which significantly increases the boiling point. As water boils off, the temperature of the boiling solution increases. With a jam, Harold McGee writes in On Food and Cooking that you're going for a concentration of about 65% sugar, which will have a temperature of between 217 and 221°F.
Once you've added yourself enough sugar and dissolved it into the water, you have to eliminate the electrical charge on the molecules. Pectin molecules are negatively charged, which means that you need an acid, which is positively charged, in order to neutralize it. Hence the addition of lemon juice or similar to your typical jam recipe.
Okay, so why can't we double the ingredients? In order to get the sugar and water to the proper temperature, you would need to boil the liquid for much longer than you do in the recommended batch size. Unfortunately, among its many delicate qualities, pectin is also not all that fond of high temperatures for long periods of time. So, if you boil the pectin for too long, it will break down and won't gel correctly.
There are ways you can work around this problem. One of the traditional ways is to add more fruit to your jam. If you use something like apples, which are crazy high in pectin, you will have a more heat resistant jam, as the pectin is closer to the source. Pectin that you buy in the store has gone through a significant amount of processing already, and is not as robust as pectin that you harvest yourself.
Another option is to use a different kind of pectin. There are pectins, such as Pomona's universal pectin, which have had calcium added to it. Not only does calcium make for strong bones and teeth as well as crunchy beans, but it firms up the pectin as well. This type of pectin is much more robust than the unadulterated kind, and doesn't need the high concentration of sugar in order to gel. This makes it popular with people who want to make a jam with less sugar in it. These pectins are often marketed as low or no sugar pectin.
Now, given the explanation I've found about overcooking the pectin, I suspect that you might be able to add the pectin in late in the process as kind of a mitigating factor. What you'd want to do is dissolve the pectin in water to start with, then ensure that the sugar solution that you're making is concentrated enough to allow it to go back to the 65% once you've added in the dissolved pectin. Honestly, though, that sounds like a lot more work than just making two batches or using the proper kind of pectin.
Aside from the extra calculations you'd have to do for the late addition of pectin, I'd be concerned that it might not be enough. As I've mentioned, pectin is a fragile beast. Although doubling ingredients works great in two dimensions, remember that you're making a pot of jam, and this pot has three dimensions. For robust sauces, this is not a problem, as there's more than enough holding capacity to keep everything going.
To illustrate why this is a problem, imagine that you have 9 pennies, and you make a 3 x 3 square of out those pennies. Easy. Now, double your area. To do that, you simply put another 9 pennies in a 3 x 3 grid next to the first, and you're doubled. If you wanted, you could even stack the pennies on top of each other, and they'd stay just fine.
Now take a deck of cards and build a tower of cards out of them. Like this one:
If you have a steady hand and lots of practice, this is possibly but not terribly difficult. Now, add another deck of cards to that. Keep building up, or even make a structure that is twice as wide but where the horizontal cards are shared between the two sides. It's a lot easier to make a mistake and cause that structure to collapse. With a delicate sauce, I think that's a typical problem when you try to expand the recipe too much.