florence, cooked OFF some fresh sweet potato = quickly, simply cooked, may require additional cooking with other ingredients cooked UP some fresh sweet potato = cooked completey, to the desired state Florence, I'm answering you question from comments here. “Off” has many meanings. I will try to explain the idea behind “to cook off” in the context of your sentence. Off originally means “of” in very old English. A leaf of a tree is similar to a “leaf off a tree”. Figuratively, a tree leaf undergoes a change of state to become a leaf “off” a tree. “Cooked off some sweet potato” signifies that you simply changed its state from raw to cooked. If you finish off a steak, you change its state to “eaten”. If you dash off a letter you quickly change its state to “written”. If you kill off a bear, you change its state from alive to dead. If you turn off a light you change its state from on to "off". To cook off a food is kitchen jargon for pre-cooking something as part of a larger recipe. ------- Hamster food recipe. http://www.rodentswithattitude.co.uk/forum/showthread.php?t=6559 Cook off some potato peelings, drain them and leave to cool. Mix with a handful of broad bran. Recipe for Fritters Cook off some good quality bacon until it’s nice and crispy, at least that’s how I like it, then drain it on some kitchen paper and allow it to cool a little before adding to your fritter mix and cooking as normal. Side dish of Spinach The suggested side for the fish was garlic mashed potatoes and raw baby spinach leaves. The idea of the baby spinach (which I love) with mash and fish just didn't gel for me. I chose to cook off some regular spinach lightly with a little grind of nutmeg served at warm room-temperature.

A "cook-off" is a competition. http://en.wikipedia.org/wiki/Cook-off "Cooking off" relates to explosives. http://en.wikipedia.org/wiki/Cooking_off "The first thing I did was cook up some fresh sweet potato." The word "up" is not necessary, but not wrong, either.

Correction: The first thing I that did was to cook some fresh sweet potato . The first thing I did was that I cooked up some fresh sweet potato . The chef means that he cooked the sweet potato before anything else.

the first thing I did was I cooked off some fresh sweet potato . = explode the first thing I did was I cooked up some fresh sweet potato . = prepare food See: http://encyclopedia.thefreedictionary.com/cook+off http://www.thefreedictionary.com/cook+up

cook up I don't know the expression "cook off".