This jam is cooked the old-fashioned way, without added pectin, and it is a two-day process. The berries themselves provide the pectin, and the jam is cooked until most of its moisture evaporates, resulting in a more concentrated strawberry flavor. When you make jam with added pectin, the added pectin "sets" all the excess water which is in the fruit, leading to a weaker-tasting jam. If you wish to make jam using pectin, there are several pectin jam recipes elsewhere on this site. I use a small amount of balsamic vinegar in the jam because it helps to bring out the flavor of the strawberries. You will use the cold plate test to check the set of this jam. I have included instructions on how to do this below. PLEASE NOTE: This is not an extra-firm set jam. It is spreadable, but it will not be one single, solid mass in the jar. If you would like a store-bought jam consistency, you should use a pectin-added recipe.