Yes, it’s important to add the lemon or lime juice or vinegar if called for in a Pomona’s Pectin recipe.
To be safe for water bath canning, the fruit mixture must be what is considered “high acid,” which means the pH must be 4.6 or below. Many fruits are high acid naturally. But fruits that are considered to be “lower acid” and/or fruits and vegetables that are considered to be “low acid,” need lemon or lime juice or vinegar added to bring down their pH into the “safe for water bath canning” range.
In water bath canning, it is the acid that prevents the growth of the bacteria that causes botulism. This bacteria likes to live in low-acid, no-oxygen environments.
One difference between Pomona’s Pectin and other pectins is that other pectins have acid added to them; Pomona’s does not. That is why some fruits in our recipes require added acid (lemon or lime juice or vinegar), even though other pectins may not require added acid for these same fruits in their recipes.
In some cases, the added acid may be also be required for the jam or jelly to jell properly with Pomona’s.
This is why, if you want to store the final product on a shelf at room temperature, it’s always important to follow a tested recipe.
If you don’t want to add acid or you don’t know whether the pH of your mixture is 4.6 or below, your jam or jelly should be frozen for long-term storage. If using glass canning jars for freezing, check to see if jars have sealed once the jam or jelly is cool. If so, you want to unseal them; then put the lids and bands back on before storing in the freezer. You don’t want to freeze (or refrigerate) in a sealed jar.
If you are converting a recipe or developing your own, go to Get Creative for information about which fruits require additional acid with Pomona’s Pectin and the amount required for each fruit.
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Posted in: 5. Questions About Ingredients: Fruit, Acid, Alcohol, Sweeteners, and Making Jam with No Sweetener