I love jellies for three reasons: one, they’re tasty and I eat them for breakfast; two, they’re extremely handy to have in the pantry, to stir into sauces or inject into doughnuts; three, they are beautiful, visually and conceptually. Actually they’re a bit like headcheese, conceptually: the cook extracts a natural thickener from the main ingredient, then concentrates it to form a network that gives the food a unique, wobbly texture.
If that piqued your interest even remotely, please, read on.
The Chemistry of Jellies
Lets start at the beginning. Unlike animals, plants get all their nutrients and energy from soil and air and sunshine. They therefore stay in one place, and require a rigid framework on which to grow. Like animal cells, plant cells are made of fluid enclosed in little sacks of a semi-permeable membrane. Unlike animal cells, they also have a firm wall surrounding their cell membranes for additional structural support.
These cell walls are analogous to reinforced concrete. Fibers of cellulose act as the iron rods, and hemicellulose and pectin act as the cement that cross-links the rods. Hemicellulose is made of glucose and xylose sugars, while pectin is in fact “long chains of sugar-like subunits,” whatever the hell that means.
Here are some things that happen when we cut and cook fruit:
- the thermal and physical disturbances break the pectin chains in the cell walls apart,
- cell membranes rupture, spilling cell fuild everywhere, and
- the loosed pectin dissolves in that cell fluid (and any other liquid you have added to the mix).
The pectin does not re-form into its characteristic chains because it has been diluted, and the sub-units can’t reach eachother. To aggravate the matter, the pectin sub-units accumulate a negative electrical charge, and so are actually repelled by eachother!
As sympathic cooks we can help pectin chains re-form by doing the following:
- adding sugar – Sugar is hygroscopic and attracts water. With water molecules flocking towards the sugar, the pectin molecules have an easier time finding eachother.
- boiling off excess water – This also reduces the distance between pectin molecules
- adding acid – Acidic solutions are full of hydrogen ions (H+) that neutralize the pectin molecules’ negative charge. After contact with a hydrogen ion, the pectin molecules no longer repel one another.
The three steps above that help reform pectin chains also happen to preserve the fruit and discourage microbial growth.
With the pectin chains re-formed, there is now a network that traps water and gives the jelly its characteristic firm-but-wiggly texture.
You can make a jelly out of almost any fruit or vegetable you can imagine. However, different plants have different amounts of pectin in their cell walls. Apples, for instance, have quite a bit. Peppers don’t, so to make a pepper jelly (like, say, the green jalapeno jelly the serve at Dadeo with their biscuits…) you have to add pure pectin (and food colouring…) Obviously these jellies can be very tasty, but I like making jellies that use the pectin that occurs naturally in fruit. Pectin-low fruit, like rosehips, can be cut with apples or crabapples to boost jelly-forming power.
Making Clear Jelly, with Clear Flavours
Step One: Mash. In traditional jelly-making, cooks extract the flavour and pectin from fruit using a mashing technique. The fruit and cold water are combined in a pot so that the fruit is just, just covered. Adding excess water will dilute the flavour and pectin. The water is brought to a boil and the fruit is simmered until just, just tender, as overcooking will muddle the flavour of the fruit. Once tender, the fruit is smooshed with a fork or potato-masher or some improvised fruit-smoosher. Typically the mash is removed from the heat and left on the counter for fifteen minutes so that the flavour and pectin moleclues can leach into solution.
Step Two: Strain. One reason that jellies are no longer cool is because they have a refined, Victorian, clarity, while the modern diner prefers natural, rustic presentations. At the expense of a bit of flavour, and a bit of wasted fruit, jellies are strained so that they shine like Swarovski crystal.
The fruit mash is transferred to a strainer set over a container, and left to rest for several hours. The strainer, traditionally, is a jelly-bag, but towels or perhaps a chinois could be used, though I’ve never tried them. It’s important to let gravity do the draining for you: don’t press on the mash or you will cloud the jelly.
Step Three: Add sugar. The exact amount will depend on the fruit you are using. For a strained fruit juice with a specific gravity of 1.032, I add 400 g of granulated sugar for every 600 mL of juice.
Step Four: Boil. Boiling rapidly will keep the flavour fresh. This applies to stock reductions, as well as jellies. To ensure clarity, as we concentrate the pectin by boiling the jelly, we skim any foamy sludge that forms on the surface, just as when reducing stock.
We can judge, roughly, when we have concentrated the solution sufficiently by measuring its boiling temperature. The more solids that are dissolved in our jelly, the higher the boiling temperature will be. As we boil and reduce the liquid, the temperature will rise. This is a fairly reliable method, but it’s not perfect. Even if we know the amount of dissolved solids, we’re not sure exactly which of those are simple sugars, and which are pectin. For most jellies, I stop boiling at 218°F.
Step Five: Jar. Once you’ve reached the right temperature, the jelly needs to be transferred tosterilized jars immediately. If you remove the jelly from the stove and let it stand, it will start setting up, and when you go to pour it into the jars it will be clumpy. Once the jelly has started to set, in my experience it will never be smooth again, even if you return it to the boil and try to whisk out the lumps. Besides being clumpy, the jelly will not be as firm.
Jelly Making: A General Procedure
- Put acidic, pectin-rich fruit in straight-sided pan. Add water until fruit is barely covered.Bring fruit to a rapid boil and cook until just-tender. Remove pan from heat. Mash fruit and let stand for fifteen minutes.
- Pour mash into a jelly bag, suspended over a deep pot. Let drip for at least two hours, preferably over night. Do not compress mash to extract juices!
- Measure collected juice. Scale out appropriate amount of sugar.
- Combine juice and sugar in a pot. Bring to a rapid boil. Monitor temperature until mixture is just below 220°F.
- Immediately pour into sterilized jars. Lid jars and process.
Now that you know the science of jellies, you should have no problem troubleshooting. Common problems:
Jelly did not set:
- Improper ratio of juice to sugar; namely, not enough sugar. Sugar attracts water, making it easier for pectin molecules to find each other and hook up.
- Jelly not cooked long enough, ie. not enough water has been boiled off.
- Not enough acid. Acid neutralizes pectin’s negative charge so they are no longer repelled by each other and can reunite.
- O my God, you didn’t press the mash through the jelly-bag, did you? Good.
- Jelly cooled before being jarred.
Don’t you feel empowered by all this information? Put it to good use:
- Rosehip Jelly
- Dolgo Crabapple Jelly
- Onion Jam (This recipe uses Crabapple Jelly. I know: a preserve that is used to make a preserve. Recursion.)
1. McGee, Harold. On Food and Cooking. ©2004 Scribner, New York. Page 296. This is the only direct citation I used, but really all of the scientific info is from this invaluable reference.