the mysteries and science of jam
and a story about me being stupid
Since Tuesday, I’ve eaten or cooked or drank carne adovada, mushroom bechemel baked rigatoni, ice cream cake, summer berry tart, garlic scape pesto pasta, sushi, beer, whiskey sours, and chocolate banana cream martinis. I have consumed peaches, cherries, zucchinis, cucumbers, and raspberries, all picked and then eaten within twenty-four hours. This was a week of appetite and decadence, gluttony but without the connotation of sin.
I hope you’re reading this because you like to eat. It’s officially summer, the best time for eating.
It’s also the best time for making jam. Jam is just the jarred outcome of summer and chemistry in a pot on the stove.
Summer fruit, when combined with lots of sugar, will turn into jam after about fifteen minutes over heat so reliably and magically that it could be the basis for a religion.
Unless, of course, you’re me. After making two gorgeous batches of raspberry currant and black raspberry currant jams this week, I tried for batch three with supreme confidence. I measured raspberries, currants, and sugar into a pot, turned on the gas, and stepped away until the mixture melted and boiled. I popped open the handy-dandy instant thermometer, stuck it into the pot, and read 108 degrees.
I did this about fifteen times for the next fifteen minutes, increasingly baffled by the failure of the temperature to rise. I stirred frantically, confused at how the mixture could be so far from my target — 220 degrees Fahrenheit. The mixture looked like jam, and yet…
Reader, the thermometer had switched to Celsius. And rather than follow all of the visual and experience-based clues that told me this jam was finished, I was so obedient to my thermometer that I did not question its output. I started to wonder if it was broken long before I started to wonder if I was stupid.
By the grace of science, I did not actually overset or burn the batch of jam in question. The next morning, the fully cooled mixture, while perhaps a little bit thick, could move and spread just like any jar of jam.
This was a bit of a miracle. The chemistry + summer = jam thing means that the rules of chemistry must be followed, and I nearly broke them.
Jam is thick and gel-like because of the presence of pectin, a carbohydrate that grows naturally in the skin of most fruits (very high quantities in currants, apples, citrus, etc, very low quantities in berries). When pectin dissolves in water, it can disperse throughout the jam to form a bouncy, grippy web that holds pieces of fruit evenly throughout the water. This is why, if you look at a jam jar, you should be able to spot bits of fruit scattered evenly throughout, instead of sunk to the bottom.
Pectin can form this magical web (creating a colloidal suspension, for anyone who remembers high school chemistry), but it does not naturally want to do so. The pectin molecules typically avoid each other when they dissolve, so to neutralize them into submission one must add some acid and a pretty sizable amount of sugar (at least 50% of the fruit). The sugar sucks up the water, essentially drying out the mixture, while the acid encourages the pectin to create its grippy web. Since the boiling point of water is 212 degrees Fahrenheit, the sugar also allows the temperature of the mixture to rise above 212 degrees, which is necessary to ensure that most of the water has evaporated and to “activate” the pectin web.
Hence the incident with my thermometer. The ideal temperature for finished jam is 221 degrees, which is high enough for the pectin to activate and low enough to prevent the sugar from turning into “soft-ball” candy, at 235 degrees. I must have turned the stove off before the jam hit 235, when it would have become a burnt fruit caramel. (While plenty of recipes claim that putting jam on a frozen spoon and watching it gel will let you determine it’s set, I’ve found that test to be unreliable. The thermometer is not, when used in addition to common sense.)
Making jam, therefore, does not require a recipe. It requires seasonal fruit, some additional fruit with high pectin (currants, apples, citrus, pears, or plums), something acidic (the fruit will often be acidic enough on its own), and a lot of sugar. It requires about fifteen minutes in a pot on the stove. And finally, jam ideally demands both an instant-read thermometer and someone with a brain to monitor the operation.
If you would really like some recipes for jams and jellies, this is a great use case for an older (pre 1997) edition of the Joy of Cooking…
Restaurant notes this week
great beer, even better bike ride to get there: Lost Generation Brewing Company, NOMA. The beer was great and so was the presence of a LOT of dogs.
relatedly, fatty melty crusty brisket: 2Fifty Texas BBQ, Union Market or Riverdale, Maryland.
To close us out, peaches are in season and aren’t they sexy…
