It's all about getting the amount of pectin and sugar right, and not overcooking, (thank you Thermie).
What has helped me enormously is this tutorial by a forum user. If you are reading this...rear your fabulous head and claim your recognition.
Here is the tutorial:
I absolutely adore preserve making, and use my thermomix 90% of the time, but there is a knack to getting low pectin fruit to gel, and so I am finally getting off my butt and posting in the hope that this will be helpful.
I don't use the recipes in the TMX cookbooks as I find they don't work as well as I'd like.
I don't use a lot of sugar in my jams, as I find 1:1 way too sweet for most fruits.
I can go down to 400g sugar:1kg fruit and still have it set and keep for over 12 months just fine.
I do add lemon juice to most of my jams as I love the balance of flavour it gives, and it also adds pectin.
Jam sets, when the acid, sugar and pectin levels are 'right' and when the jam has reached high enough temp. You can't normally reach that temp at 100C in the tmx, you need to go to varoma.
But first...you want to macerate the fruit. This means the fruit has 'taken up' the sugar, and release some of its water content. Once you get the hang of it, you'll be able to tell the difference, but until then, keep a relatively close eye on the mixture - if it looks like chunks of fruit floating in liquid (kind of like fruit in a punch bowl), it's not ready. If it looks like it is stewed/softened/mushy and it is more incorporated into the liquid, it's probably done.
So... Chop up your fruit (if you chop in the tmx, it will be harder to tell if the fruit is macerated) - I usually just do halves for apricots n figs 'cos I like it chunky! Liz here - I use 400g sugar to 700g fruit
Add in sugar n lemon juice (10g juice:100g sugar is a good ratio), then macerate the fruit by mixing on REVERSE, speed 2, 100C. I normally find 20 mins is enough time.
Taste the mix, if not sweet enough, add more sugar - it will only take about another 5 mins to dissolve.
Then... turn up the heat to Varoma, and put the steamer basket on top. The mix will expand, depending on how dense the fruit is, but about 700g of fruit will be the max you can use before it is oozing all over your TMX. Berries are the worst! And I can only do 500g at a time. The amount of time at Varoma you need will vary with acid/sugar/pectin contents.
For most fruit, I find 15 mins is enough, but you can experiment by putting a small plate in the freezer and dropping a blob on the plate. If it gels, it's ready, if not, keep going.
Remember also that jam will set over about 24hrs. I made some apricot jam recently that I thought was too runny but by the next morning it was perfectly soft set and oozy, just the way I like it. Remember, the longer you cook jam, the darker it goes, so you want to cook it for the least time and the lowest temp in order to get a beautiful colour.
That's why you don't just cook it at Varoma the whole time.
So Liz here. Today I did a strawberry jam and this was the recipe:
1 very large tart green apple
700g strawberries ($4 a kilo this week - WOW)
400g raw sugar
1/2 teaspoon citric acid
Method: Chopped the green apple (skin seeds and all) for 4 seconds speed 7. Then scraped down and added the strawberries and sugar. Macerated for 30 minutes, 100 degrees, reverse speed 2 with simmering basket on top.
Cooked for 19 minutes Varoma temperature, reverse speed 2 with Simmering Basket on top. (I checked it at 15 minutes and gave it 4 minutes more). You just put a saucer in the freezer, add a teaspoon of jam, put it back in the freezer and check after 2 minutes if it wrinkles when you tip it sideways.
The time will always vary depending on the natural pectin content of the fruit.
Hope this helps!