Fruit preserves have entered a certain level of ubiquity in our kitchens—topper of toast, peanut butter buddy or teatime trimming, jam is a sweet thing we eat because we always have. Some like it rife with proof of the fruit it once was, others prefer a smooth, refined spread without the seeds, please. All in all, jam seems a straightforward condiment that offers simple pleasures. That is, until you try making it yourself.
Standing over a steaming pot of fruit whose bubbles burst out in sugary magma, jam’s simplicity tangles into a thick briar of questions: Should I stir it? How often? Is it done? Why is it covered in foam? And when you pop open your first jar and the jam is spreadable or it isn’t, the fruit has held something of its delicate flavor and texture or it hasn’t, the gel has set too thickly or not quite enough, the questions multiply.
Jam truly is a balancing act, finding that place on a seesaw of fresh flavor and just-so gel where the two sit still and look across at each other for a moment, one holding the weight of the other; and from that spoonful of strawberry preserves in January, you can see right through to a summery spring day at the market when your arm was slung around a flat of fragrant berries.
To achieve that balance, a preserver must transform fruit while interfering as little as possible with its flavor and texture. The three basic tools at her disposal are sugar, acid and pectin. Sugar, in moderation, helps develop the jam’s flavor profile, activates pectin, and is a preservative, inhibiting bacterial growth by displacing water. Acids (usually lemon juice and/or rind) function similarly to sugar, though their preservative role is to lower the solution’s pH, which also halts most bacterial growth.
Pectin is jam’s most finicky ingredient, as it is (in truly great preserves) not an additive but something you coax. Though many know pectin as a white, finely powdered substance added to jams along with copious amounts of sugar, pectin is already a component of your main ingredient’s cellular structure.
A carbohydrate, pectin binds the fibrous components of cell walls and increases as the immature fruits grow. When a fruit begins to ripen, pectic enzymes break down the cement-like structure of pectin and allow the cell walls to soften and expand with sugary solution. Thus, fruits that are just under ripe (still a little firm) boast the highest amounts of natural pectin.
Some fruits contain enough natural pectin to avoid adding a supplementary source at all. Apples, quince, cranberries, blackberries, gooseberries, plums and citrus rind will generally gel without added pectin. A traditional technique for attaining naturally gelling jam is to use one-quarter under ripe fruit and three-quarters fully ripe fruit to split the difference between flavor and pectin availability. Blends of high and low pectin fruits are another old-timey trick, such as adding tart apples to cherries or raspberries to increase their gel.
Citrus rind and apples (or crabapples) are such a great source that commercial producers isolate pectin from them using refining techniques. However, to activate commercial pectin, you must add large amounts of sugar. This alters the end product’s flavor by masking its subtleties with sweetness and watering it down, as the commercial pectin solidifies excess water rather than evaporating it.
Pectin is composed of long chains of sugar molecules that, if properly cajoled, bond with each other, forming a net-like matrix that binds liquid into gel. Pectin has a slight negative charge in water, and naturally resists bonding. Acids help diminish that negative charge, but water-attracting sugar is also necessary to decrease water content and act as a bridge between pectin molecules. Boiling further reduces water through evaporation and provides the magic temperature (221° Fahrenheit), at which pectin and its saccharine mediator connect and create a gel.
Getting a good ratio of these three components is both science and art. It’s important to follow a recipe in detail, without cutting sugar or other ingredients, until you have a firm grip on which ratio produces jam of a consistency you like. This ratio will be different for each kind of fruit you preserve.
Savvy preservers also avoid the need for refined pectin by making batches of green apple pectin concentrate with the fall’s first harvest. Freezer stored pectin concentrate will wait at arm’s reach for the first fruits of summer that compel you to seduce them into a jar.