Cooking For Engineers

[topaz]

It's marmalade making time (at least here in Europe, even more so in the UK).
Yesterday I made a batch and, even after following all the instructions (including a 24 hour cold soak), it did not set.

There are roughly 5 parts to an orange:
skin, pith, membrane (around segments), pips and flesh, where skin + pith = peel

Does anyone know which parts supply what proportion of the pectin?

I suspect mine failed because I put everything except the flesh and chopped up skin in a muslin bag, and this bag was probably too tightly tied, not letting the pectin escape.

I am planning a new strategy:
- wash and half oranges,
- squeeze out juice
- clean membrane out of skins
- put everything together loosely in a pot with added water
- boil till peel is soft
- cool a bit, take out peel, strain the rest
- chop up peel, add to juice, add sugar
- hard boil to setting.

The idea being to maximise the pectin extraction and distribution.
This is engineering ! !
Any comments ?

[Dilbert]

I am far from expert in this area - but some quick research says oranges are in the "high" group so far as pectin goes, and it's mostly in the peel.

that said, pectin content is variable - most people I know use some extra pectin "just to be sure"

I did trip across an interesting and simple "test" - add 15 ml of rubbing alcohol to 1 ml of your cooled juice. if it congeals nicely, you're okay. small gel clumps or no gelling indicates insufficient pectin . . .

[topaz]

Thanks for your reseach, Dilbert.
Having read that I also did some Googling and found, like you, that it is the peel that contains the pectin.

So why do all recipes say you should put the pips in the muslin bag ?
(In fact, before today, I would have said that the pectin was in the pips; I am sure that is the "cook's" opinion.)

Since peel = skin+pith and skin is only a few microns(?) thick, it is probably the pith which contains the pectin. Which is why this is put in the bag.

Interesting tip about using rubbing alcohol to test setting. The temperature would have to be quite low, I expect, to stop the alcohol evaporating.
Food, or rather, jam for thought.