Grapefruit is Citrus wood and Grape is grapevine, both can be used for cooking. Grapefruit is the typical wood you would get if you were buying Citrus as the trees are larger than the Orange or Lemon varieties and yield more wood, Citrus trees are a pain to cut, tons of twigs and small branches, hidden thorns, short trunks, wild growth patterns etc....
Citrus will not give you a sore throat or make you sick in any way if the wood is well seasoned, in fact it is one of the most hypoallergenic wood types available!
Unfortunately most of the big orchards we grew up with in the Phoenix area have been removed and the wood is actually getting scarce, add the higher labor and lower yield, it makes it a wood not offered for sale as often as in the past. Citrus can be used like all fruit wood for smoking, it does burn to a talcum powder fine ash but it also burns real fast, one of the cleanest burning wood types available! (Unlike Pecan or Oak, both of which can be used on the green side, Citrus must be well seasoned for using to cook)... Hope this helps, Thomas
