Quince jam carries a colour entirely different from the fruit. Raw quince is yellow while its jam is deep red. Measurable chemistry lies behind that change.
Why does the colour change?
Quince contains a high quantity of tannins.
Tannins are phenolic compounds found in plants.
Those compounds sit colourless or pale yellow in raw quince.
Meeting heat and oxygen they polymerise; they bind to one another and form larger molecules.
Those large molecules absorb light in red and brown tones.
The result is the jam turning red; the same reaction is why tea darkens as it brews.
| Cooking time | Colour | Consistency | Aroma |
|---|---|---|---|
| 30 minutes | Pale yellow | Runny | Fresh fruit |
| 60 minutes | Orangeish | Medium | Balanced |
| 90 minutes | Light red | Thick | Caramelised |
| 120 minutes | Deep red | Very thick | Intense |
| Over 150 minutes | Burgundy-brown | Setting hard | Bitter |
How does cooking time determine the colour?
The colour depends directly on time.
No clear change happens in the first thirty minutes.
An orangeish tone appears by the sixtieth.
A light red forms at ninety minutes.
A deep red comes at a hundred and twenty; that is the colour most recipes aim for.
Past a hundred and fifty minutes the colour shifts from burgundy to brown and caramelisation leaves a bitter taste.
What role does pH play?
An acidic environment slows the tannin reaction.
Adding lemon juice delays the darkening.
That looks like a disadvantage but in fact provides control.
Lemon juice is also necessary for the pectin to gel.
Pectin works best between pH 2.8 and 3.5.
The lemon juice therefore goes in toward the end of cooking; acid added once the colour has developed both delivers the consistency and stops the colour darkening further.
What separates covered from uncovered cooking?
Oxygen is necessary for the polymerisation of tannins.
The mixture meets air continuously in uncovered cooking.
The colour darkens faster.
Oxygen stays limited under a lid; the colour stays paler.
A lid also traps steam and slows the loss of water; that delays the setting of the consistency.
Traditional recipes prefer uncovered cooking; both the colour and the consistency develop at once.
What advantage does quince hold in pectin?
Quince is among the fruits highest in pectin.
One to one and a half grams per hundred.
That value runs 0.5 to 0.7 in strawberry and peach.
Quince jam therefore needs no added pectin.
The fruit provides its own consistency.
Most of the pectin sits in the skin and the core; traditional recipes therefore wrap the cores in muslin and include them in the cooking before removing them.
How does the consistency get controlled?
The consistency of quince jam can set too firm easily.
Where high pectin meets long cooking the product passes the consistency of jelly.
The test is simple; a drop of jam goes onto a cold plate.
It waits thirty seconds.
Where the surface wrinkles under a finger the consistency is ready.
The cooking stops immediately where that test passes; jam left a minute longer on the heat sets firm enough to cut once cool.
How do the slices of quince get prepared?
Quince is a firm fruit and preparing it takes time.
The skin gets peeled but not discarded; it goes into the muslin as a source of pectin.
The fruit gets grated or diced.
Grated quince gives a more even jam.
Diced quince leaves pieces in the section.
The cut fruit goes straight into water with lemon; quince meeting air darkens fast, and that darkening is an unwanted result, unlike the controlled change of colour during cooking.
How does quince jam get stored?
Quince jam carries high pectin and high sugar.
Those two properties provide a long shelf life.
An unopened jar holds two years on a cool, dark shelf.
A month in a fridge once opened.
Where the jar was sterilised and filled hot a vacuum forms and the shelf life extends.
A clean spoon gets used; a knife that has spread bread brings crumbs and moisture into the jar, and mould can begin despite the high sugar.
How does quince jam get served?
Quince jam finds a range of uses different from other jams.
It gets spread on bread at breakfast; being firm in consistency it can also be cut into slices.
It goes out with clotted cream; that is the traditional and most widespread pairing.
It works with white cheese too; the contrast of salt and sweet sits well with the astringency of quince.
It goes out as a dessert; a slice or two on a small plate with walnuts over it.
It gets used as a filling for cakes and tarts; thanks to its high pectin it does not run in the oven.
It appears alongside meat dishes too; it forms a classic pairing with duck and lamb.
It gets stirred into yoghurt; being firm it first gets thinned with a spoonful of hot water and then joins the yoghurt.
What proportion of sugar applies in quince jam?
Because the fruit's own sugar runs low the proportion gets calculated differently from other jams.
Six hundred to eight hundred grams of sugar per kilogram of prepared quince.
That is a higher proportion than strawberry jam.
The reasons are the astringency of the quince and the long cooking.
Reducing the sugar breaks the balance of taste and shortens the shelf life; the high pectin provides the consistency but the preserving effect comes entirely from the sugar.
