Raspberry jam making and lemon juice..

What an industrious lot you are, thank you for all your input. I’ve made three big jars and a small test pot to try later with some fresh bread!

I always put a saucer in freezer before I start, also prepare my jars by putting in oven at low temperature with lids in bowl - pour boiling water over them to sterilise.

I don't add any water - just heat raspberries slowly so they release their juice. Cook for about 10 minutes before adding sugar - same amount as fruit - eg 1 kg sugar to 1 kg fruit. Yesterday it was 1.5 kg each. I don't make in big amounts at a time.
After adding sugar and bringing to the boil, stirring frequently, I boil for about 10 min before testing for set. Put a spoon of jam on chilled saucer -back in freezer for another 5 min while continuing to cook jam then check if it's setting. Usually that's enough cooking. I pour immediately into hot jars, put on the lids and screw up tightly. The jam will keep for months unopened.

I made plum jam recently and used just jam sugar although plums are supposed to be fairly high in pectin. Normally I'd use lemon juice.

It would not set so I boiled it for longer, worrying that it would be like cement.
It's made a rather sloppy but delicious jam.

I'd always use lemon juice n future.

Until I downsized to my gardenless flat, I have been making Raspberry jam my whole life and have never used/needed any additives to ensure a good set. I always considered Raspberry as the easiest jam to make.

I make lots of raspberry jam every year - made some yesterday! I never use jam sugar or lemon juice and it sets perfectly well and has a good colour. I've also got lots of autumn raspberries.

I do as it gives a brighter colour I think but it's a personal choice.
If you are using sugar with added pectin you won't need it for setting purposes. If your sugar doesn't have pectin you still shouldn't need it for setting but it'll take a tiny bit longer to get there.