OK I finished making the quince jelly today. Just like the crab apple jelly I only got about 800mls of juice from 2kgs of fruit. I ended up with 4 small jars. I think I must have put it in the jars too soon (i.e. too hot) as there are a lot of little bubbles through it. At least there's no scum like the crab apple jelly though! It tastes nice quite a sharp fruity flavour, will be nice with roast meat like lamb.