The Cottage Smallholder

I came across this thread while looking for some connection with quinces, so I did a bit of research, and found the following:

There are lots of anthocyanins in quinces, they are just all bound up together in big molecules called tannins. The tannins make the fruit unpalatable. To make the fruit edible, the tannins need to be broken down into smaller parts and to do that you need heat or acidic conditions. Once you heat up the colourless tannins, the coloured anthocyanin pigments are released.

Tannins cause the proteins to clump together and stick to particles and surfaces, increasing the friction between them.

The tannins in the quinces are destroyed when cooked, while the delicate rich flowery aroma of a raw quince is maintained, turning the hard, tannic, astringent fruit into a softened and milder flavoured fruit.

Usually cooking is an enemy of colour, but this is one of the few occasions that cooking actually creates colour, because the heat breaks down the bonds between the pigment units in the tannins. Not only does cooking release pigments, but the addition of lemon juice created a little acidity helps the colour compounds to stabilise. The result is the light yellow quinces become a deep ruby colour, due to the red colour of the released pigments.

Quinces have a high level of pectin and are therefore particularly good in preserves.

The reason is because today, after cooking quinces and straining them (to put into a crumble), I had a pint of beautiful deep red quince juice, and so decided to make a couple of small pots of quince jelly. Due to the high quantity of pectin, it set after only 5 minutes of heating, and is gorgeous, both in colour and flavour.

Amazing, eh?