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when is it too late to add sugar when making jam?

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just finished making my first ever concord grape jam. It's really tart and probably over cooked. I kept adding sugar and finally gave up and just canned it. I'll know in the morning.

when you add sugar to something like jam does each addition have to cook a certain amount of time making the total cooking time longer? or does it just effect the sweetness?

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  1. How much sugar did you put in to begin with?

    Jam should be about 2/3 sugar by weight. Even with lemons, that's pretty sweet.

    The amount of time you need to cook it is however long it takes to get to the right temperature - about 105 C / 220 F - which is known as the setting point. Basically, you need to boil away enough of the liquid to raise the temperature to that point (as the sugar concentration increases, the boiling temperature of the mixture rises).

    If the sugar concentration is too low, the jam can go moldy much more easily, and isn't suited to long term storage, or storage at room temperature.

    6 Replies
    1. re: tastesgoodwhatisit

      thanks. It was pretty late last night. I should have added more sugar sooner. I had about 4 cups of pulp + the skins. But it did get me started wondering why cranberry sauce/jelly was so easy and this was such a long and difficult process.

      I live at 5400 ft. and kept trying to get the temp past 200 but finally just gave up. I think it jelled enough but probably could have cooked down a bit more. Lots of work for 6 pts. of jam. Next time should be better. The grapes may not have been ripe enough. Now I'm trying to figure out another use for this batch besides on toast, or ice cream or just about anything. Will check out peanut butter! Any suggestions? I really appreciated your response.

      1. re: wyowy

        Cranberry sauce practically makes it self because cranberries are absolutely LOADED with pectin. Making jam/jelly with other fruit can be challenging... and it needs a TON of sugar in it from the beginning or it'll never 'gel'.

        1. re: Kajikit

          When making jam from low pectin fruit I use the white pith from lemons for extra pectin - I put it in a cloth bag and toss it in while boiling the fruit, removing before it gets to the jelling stage.

          Jam making's not all that popular where I live, so pre-made pectin isn't readily available.

          1. re: tastesgoodwhatisit

            how much pith does it take?.....and just want to be sure I understand..the sugar does not make the jam or jelly gel? So if my jam is getting close too done but still too tart I can still add sugar at that point?

            I thought everyone loved jam:-) but these grapes skins have kind of a sharpness that might interfere with the taste of the final product. I think someone suggested pureeing the skins and them adding them back to pulp. I think using only part of the skins would be better but how would you adapt recipe (could use less sugar?) would this give you the same deep purple color?

            thanks for all the info. will try lemon pith in the future.

        2. re: wyowy

          Did you add pectin, or just the grapes and sugar?

          Since you're at altitude, cook jam to 8 degrees F above whatever the boiling point is there. So, 220 at sea level, a few degrees lower for you.

          1. re: babette feasts

            did not add pectin. thanks for the info on the boiling point.