I have a tendency to only use preserving sugar unless I'm working with strawbs, then it's always jam sugar.
That's interesting. I have read a lot of books on preserving and apart from one guy ( Oded Schwartz) they all say not to use preserving sugar for jams, jellies & marmalade. Oded 's recipes suggest using either granulated or preserving sugar.
Silver Spoon says that their preserving sugar is made with larger crystals which heps prevent burning and is ideal for "high" pectin fruit preserves
http://www.silverspoon.co.uk/products/baking-and-cooking/preserving-sugars/preserving-sugar. So this wouldn't be any good for low pectin fruit like cherries and it is more expensive to buy than granulated. I'm not sure it is worth it because I haven't experienced any problems with using ordinary sugar that they claim using preserving sugar prevents...i.e.burning, less froth, or cloudy jellies. I wonder if it isn't just a marketing gimmick
As we have to watch the costs of everything we make really carefully I couldn't justify the extra money but can see it might be worth using for just home use. Have you used it when making low pectin fruit jams etc?
Jam sugar is ok but it does cause a lot of froth and you have no control over the amount of pectin you are using as it's already mixed in with the sugar. If you wanted to use slightly less sugar you would also be using less pectin automatically.
Also I can tell the difference in taste and consistency of jam made with jam sugar - strawberry for example tends to have an after taste and sets quite solid which isn't always very nice. I do sometimes use half jam sugar and half granulated if following Pam Corbins Strawberry Jam recipe and this produces a lighter set (but lots of froth). Scraping off the froth can lose you a lot of your precious jam as well.
Making jam is great and I love it ...until I hit a problem and then I blame myself (quite often the case) but when you start reading the so called experts opinions and advice you realise they all have their own take on what is right or wrong and in the end if it works for you then go with it.