Help.Jam that refuses to set

I made my strawberry jam a couple of weeks ago, used many different sizes of strawberry and it didn't set. I use a thermometer to check the temp plus the cold plate test. I poured it all back into the pan and boiled it till it was a degree over the indicated temp and hey presto it worked. I think I thought it would become solid if i wasn't absolutely precise.

Strawberries are usually low in pectin. Did you add any? Over ripe fruit seem to lose a lot of pectin, even in Gooseberries.

I had used Certo! Tonight I have re boiled it, filled the jars and put said jars on a top shelf. I'll check after my holidays....shouldn't even have jam as my target weight waves bye bye.

I haven't made jam for years as we have no garden to grow fruit. I always made strawberry and apple jam, a tip I got from my mother. She always found strawberries alone were difficult to make set. The best jelly I ever made was apple and elderberry. It was delicious.

Someone once told me that strawberry jam sets better with under-ripe rather than over-ripe fruit.

I once added a few cubes of strawberry jelly when the jam wouldn't set. Bring jam to boil, drop in jelly and mix, then allow to cool.
It worked but was too sweet, so maybe some lemon too.

I'm going to experiment a little more this year. I always make a range of fruit jams and also make fruit cheese with the leftovers from making fruit jellies. My family always to prefer the 'mixed fruit' jams I make with the odds and ends of fruit that otherwise would hang around in the fridge. Rhubarb and strawberry was a hit last year, also gooseberry and blackcurrant and rhubarb and ginger. I made some strawberry and elderflower jam last year too - using home-made elderflower cordial in place of some of the sugar - it was a lovely flavour, but I rarely write down exactly what I do so sometimes I can't easily replicate the recipe.
This year my blueberry plants are full of fruit so I'm hoping to make blueberry jam for the first time. Sadly the cherry tree hasn't produced much fruit at all, in spite of having plenty of blossom in the spring, so my hopes of making cherry jam are dashed for now.
I don't eat sugar any more so my husband and children (and grandchildren) will be the major beneficiaries of my industry this year.

jenn - I'd throw it into the microwave with the juice of one or two lemons stirred in and boil it until you get the consistency you want. (Because it's already been cooked you risk it burning on the bottom of the pan if you re-boil it on the stove top.)
I never use Certo, preferring to use other fruit to give the desired amount of pectin - commercial pectin usually needs more sugar than I like to use.
This has a recipe to make your own pectin.

Yes, Certo should do the trick, or apples. I've had difficulties with strawberries sometimes as they're quite low in pectin. I've reboiled it all without any additions, just kept it going for ages until it does as it's told

Gooseberries would work to.

I would lob a bottle of Certo in or apples, ( aren't they a natural source of pectin?)
Alternatively call it coulis!

Could it be because the strawberries are too big & extra juicy?

Depending on how much you've got, you could bottle it & use as sauce over ice cream & yogurts?

Otherwise I think you might have to buy a bottle of pectin such as Certo & reboil it all. Bit of a pain but worth it for homemade strawberry jam.