Frozen berries (no sugar added) may be substituted for fresh. Thaw and drain before measuring. For thinner jam, use juice as part of the 2 c berry amount. You may decrease the amount of sugar, but it will produce a thinner result. More sugar will make it thicker. For best results, sugar substitutes are not recommended. The average refrigerated life of jam is two weeks; up to several months frozen.
NOTES : Jam requires only 3 ingredients; berries, sugar and lemon juice. I haven't yet made the jam recipe that came with my