Jam making Help

[taff]

I think if you try and re-boil it, you'll end up with incredibly tooth achingly sweet jam, because the amount of sugar you added was for the total weight of fruit and water if you see what I mean.
Logically [this is where it falls down] can you get hold of the same quantity of fruit, simmer that until soft, then add to the orginal stuff you have that hasn;t set, then boil to set temperature?
An yone and everyone is free to point out any [probably many] flaws in my reasoning....

[MaureenAB]

Yes I have more fruit. I did 2lb gooseberries 1 1/2 pints of water and 3lb sugar. If I do more fruit presumably with no water would I have to add more sugar as well? Sorry to be so dumb about this. I appreciate that you are helping me.

[taff]

don't thank me yet
I'm just now boiling up some apples to help set my unset plum jam although flummerys idea of using crab apple juice to stuff low in pectin is one I'll use next time
I'd go with simmer the fruit you're going to add, add the unset jam, taste it, if it needs more sugar, add it, otherwise boil to set point.
I used a jar of certo on a quince jelly that went horribly wrong early this year. It didn't work.
Honestly, there are various options open to you to try, have a think before you act, and someone with more knowledge about disasters may be along soon

[MaureenAB]

I did it and it has worked. Now i can say t h a n k y o u.

[MaureenAB]

What a great website. I have more jam to make so I will keep this my favourites now.

[MaureenAB]

Now I have success with jam I want to try a lime marmalade anyone have a good but easy recipe that works well first time please

[claire70]

I'm also a novice jam maker and am also having trouble getting my latest batch (plum) to set. I bought a thermometer but I don't understand what use it is, to be honest! I read the setting point is 105 c, yet my jam got to 105 c really quickly, but was clearly nowhere near ready to set. It was still really runny (and still is fairly runny, about 2 hours later). So when people like Taff above say 'boil to set temperature' - I don't understand!

Help appreciated! In this particular case I think I put in way too much water (even though it was only 2/3rds of what the recipe said), but it would still be nice to know generally what the heck thermometers are there for...