Why You Shouldn't Add Extra Fruit To Homemade Jam
In certain cases, the saying that a little goes a long way is so undeniably true. And this is always the case when you're making homemade strawberry jam with leftover fruit. Even though 1 cup of strawberries looks, well, like 1 cup of strawberries, in reality, that cup expands in the pot as the fruit is cooked down. So if you add a little too much, you'll get strawberry syrup with loose chunks of fruit floating about.
Making jam at home is an art that requires little to no practice –- just combine sugar, fruit, and acid in a pot and let it simmer (via NYT Cooking). But to make the perfectly set jam, you have to know how much of each ingredient to use, putting into consideration sugar to fruit ratio and pot size. The most common way beginners mess up their jam is by using way too much fruit, and there is a scientific reason for this.
Too much fruit equals runny jam
Home cooks forget that while they cook down the fruit, it eventually increases in volume, per Serious Eats. Although jam is mainly made up of cooked fruit, too much fruit makes for an inconsistent texture of chunks of fruit in soupy syrup. The science behind this phenomenon is simple: When fruits are cooked down with sugar, the skin and core of the fruit release pectin, which is a natural binding or gelatinizing agent, per Science of Cooking. However, not all fruits are made the same: Some fruits like gooseberries and plums have more pectin than fruits like strawberries and blueberries (via Spruce Eats). So it isn't just the amount of fruit you use for your jam, but also what kind of fruit you select.
During the boiling process, the liquids are evaporating while the pectin sets the jam together (via Science of Cooking). The problem arises when there's too much fruit, which leads to too much liquid. Not only does this make a mess, but it also prevents the liquids of the jam from evaporating, which is a necessary step in making jam. In this kind of situation, pectin can't work its magic in binding the jam together, resulting in a runny jam.