Hi west - Blanch then freeze.
Trim off any woody parts and large leaves. Wash in salted water, cut in to smallsprigs. Blanch, cool & drain well before packing in to freezer container. Thin stems 3 mins,
med stems 4 mins, thick stems 5 mins. www.allotment.org.uk Type in to the search bar, blanching veg.
i bought two medium heads of it last friday and we've just had one this evening. we'll probably have the other one thursday or friday, and i'm sure it will be fine until then. they're both green and fresh looking without a hint of brown/yellow. i just keep it in the fridge in the bag i put it into when i buy it..
perhaps it's not very fresh when you buy it as i would reckon to keep brocolli a week in the fridge before it starts discolouring.