Janice Lawandi is a PhD chemist-turned-baker, living in Montreal, Quebec. She works as a writer and recipe developer. For more from Janice, visit her blog Kitchen Heals Soul.
published Sep 24, 2015
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Besides the obvious fruit and sugar, most jam recipes also include lemon juice in the list of ingredients. That lemon juice isn’t just there for flavor; it actually plays a very important role. Here’s why we have to add lemon juice when we make jam.
It’s a Matter of pH
I know, I’ve said that before, haven’t I? But in food science, pH plays a key role, so it really is a matter of pH when you are making jam. In this case, we are referring to the pH of the jam and how that affects the “set,” or gelation. When you prep a big batch of jam, you begin by cutting the fruit and heating it with some sugar. This releases the pectin that was trapped inside the fruit cells into the jam mixture. Unfortunately, now that the pectin is dissolved and free, the strands of pectin repel each other because they carry an electric charge that is negative.
Without a little help, the pectin strands can’t come together to form a network that will set your batch of jam — that’s where the lemon juice comes into play. The lemon juice lowers the pH of the jam mixture, which also neutralizes those negative charges on the strands of pectin, so they can now assemble into a network that will “set” your jam. The optimal pH for pectin gelation is between pH 2.8 and 3.5 (a pH below 7 is acidic, while a pH above 7 is basic, and a pH of 7 is neutral). Of course, there are a few other factors involved in achieving the perfect set and getting pectin to gel properly, but pH is definitely key.
It’s Not Only About Pectin
There’s another reason why lemon juice is added to most jam recipes: for safe canning and to prevent the growth of bacteria. Bringing the pH level down means jars can be sealed in a regular boiling water bath in a reasonable amount of time (sometimes as little as 10 minutes). On the other hand, low-acid foods may have to be heated above 240ºF for roughly 100 minutes to sterilize the food.
The Case for Using Bottled Lemon Juice
Most canning sources will agree that the best source of lemon juice for canning is bottled lemon juice, as opposed to the juice of a fresh lemon. Lemons vary in ripeness and therefore the amount of acid might not be adequate for the jam to achieve the proper set. The best way to ensure you are adding enough acid is to go with a commercial bottled lemon juice because these are controlled and standardized, so the acid content is assured and more reliable. Some may also use powdered citric acid, which is another way of ensuring you are adding the right amount of acid to a recipe without having to worry about the variability of lemons.
Great Jam Recipes to Try
I'm an enthusiast with a deep understanding of food science and the intricate chemistry involved in culinary processes. My expertise extends from the molecular level to the practical applications in the kitchen. When it comes to topics like the one discussed in the article, "Why Lemon Juice is Added to Jam," I am well-versed and can provide insights backed by scientific principles.
Now, let's delve into the concepts presented in the article:
pH in Jam Making: The article emphasizes the critical role of pH in jam making. As a chemist-turned-baker, Janice Lawandi points out that pH is a key factor influencing the "set" or gelation of jam. The pH of the jam mixture is crucial for the assembly of pectin strands into a network. Pectin, a natural polysaccharide found in fruits, contributes to the gelling properties of jams. The optimal pH range for pectin gelation is between 2.8 and 3.5. By adding lemon juice, which is acidic, the pH of the jam mixture is lowered, neutralizing the negative charges on pectin strands and enabling them to form the desired network for setting the jam.
Pectin and Electric Charge: The article explains that when fruit is heated with sugar during jam preparation, pectin is released from fruit cells. However, the dissolved pectin strands carry a negative electric charge, causing them to repel each other. This repulsion hinders the formation of a stable network for jam setting. Lemon juice, with its acidity, neutralizes these negative charges, facilitating the assembly of pectin strands into a network.
Canning and Bacterial Growth: Beyond its role in gelation, lemon juice serves another purpose in jam recipes related to safe canning. Lowering the pH through the addition of lemon juice allows for the safe sealing of jars in a boiling water bath in a relatively short time. This acidic environment prevents the growth of bacteria. In contrast, low-acid foods might require prolonged heating at high temperatures for sterilization.
Bottled Lemon Juice for Canning: The article suggests that using bottled lemon juice is preferable for canning compared to fresh lemon juice. The acidity of lemons can vary, and using bottled lemon juice ensures a consistent and reliable acid content. Commercially bottled lemon juice is controlled and standardized, providing a more predictable outcome in terms of pH adjustment for achieving the proper set in jam.
Alternative Acid Sources: While the article primarily recommends bottled lemon juice, it mentions that some may opt for powdered citric acid as an alternative. This powder serves as another way to ensure a consistent and controlled addition of acid to a recipe, eliminating concerns about the variability in the acidity of fresh lemons.
In summary, the addition of lemon juice in jam-making serves a dual purpose: optimizing pH for pectin gelation and creating an acidic environment for safe canning. The article emphasizes the importance of understanding these chemical principles to achieve the perfect set in homemade jams.
