[chris (OP)]

Broccoli kept in the fridge for a while invariably turns a bit yellow on the tips; why does this happen and, despite the colour change, does it remain edible?

Chris

[Bored chemist]

Broccoli isn't edible in the first place.
(probably about the only thing that I agree with G Bush about)

[glovesforfoxes]

I've eaten it before, didn't taste any different! When there is significant yellowing I throw it away though []

[JimBob]

The yellow color that begins on the tips of the floweretes is the flowers maturing. Yes, it is edible.

[chris (OP)]

I agree with most of the above (I disagree with BC as I actually really like broccoli; in my opinion it's a star vegetable!).

Anyway, I've been thinking about the yellowing question and it must reflect chlorosis - chlorophyll break-down - probably as a consequence of cell senescence or the effects of cold.

I think the effect and mechanism is similar to the change in colour seen in autumn leaves.

[Bored chemist]

OK, so there's no accounting for taste. Is a star vegetable related to this?
http://en.wikipedia.org/wiki/Carambola

[glovesforfoxes]

Oh wow - I sure would love to try a starfruit! They look really pretty & tasty []

[Geezer]

Much as I hate to, on this occasion I have to agree with JimBob. It's flowering.

You could always pretend it's broccoflower.

[AllenG]

The yellow color that begins on the tips of the floweretes is the flowers maturing. Yes, it is edible.

Yep.
Steam it and squeeze a lemon on it afterwords and you have something I love more than about any vegetable.
Squeeze the lemon on it before you steam it and it really turns yellow. 

[Don_1]

I have to go along with Chris, I think it is most likely the breakdown of the chlorophyll. Although the broccoli flower is yellow, they grow on the opening florets like this:


I don't think this is what Chris was referring to in the 'yellowing'.

BTW, BC, if you were married to my Mrs, you'd be in a living hell. I'll swear she's got shares in a broccoli farm! Broccoli with this, broccoli with that, broccoli with broccoli, broccoli with just about everything and anything. If they made broccoli ice cream she'd buy it.

[chris (OP)]

Yep.
Steam it and squeeze a lemon on it afterwords and you have something I love more than about any vegetable.
Squeeze the lemon on it before you steam it and it really turns yellow. 

That's interesting - I'll have to give that a go. Presumably - from a science perspective - another acid would work too...anyone want to do a test?

[JimBob]

Yep.
Steam it and squeeze a lemon on it afterwords and you have something I love more than about any vegetable.
Squeeze the lemon on it before you steam it and it really turns yellow. 

That's interesting - I'll have to give that a go. Presumably - from a science perspective - another acid would work too...anyone want to do a test?

Sprinkle a bit of terragon in the water - or a little less on the broccoli - before you steam it and then add the lemon juice.

Result: Gourmet Broccoli

[RD]

... Broccoli with this, broccoli with that, broccoli with broccoli, broccoli with just about everything and anything.
 If they made broccoli ice cream she'd buy it.

Sounds familiar ...

[I bet the Queen says the same about swan  [] ]

[Karen W.]

If you leave the broccoli it will indeed flower and the yellowing is the aging and the beginning of the flowering process. If it is picked late the yellowing has already begun.. It tastes okay.. but too yellow and the flavor begins to deteriorate. the green rounded tips open up and expose their yellow blooms and then the broccoli looks less head like and sparse with flowers.

[alanan]

Broccoli tastes best straight out of the garden. The stems contain sugars which would normally produce the flower & seed. As soon as it is picked the plant starts to mature, and the sugars turn to starch, and produce a sulphur compound, which gives stored broccoli that unpleasant taste. If you want good broccoli put a couple of plants in a garden or a tub, and pick the shoots young.

[Karen W.]

Good advice!! Welcome!