I am due to cater for a very large number of people in a months time. I plan to roast pork and wanted to know; if I roast several joints of the same size(boneless loin) do I calculate the time based on one joint or the total weight of all the joints? I assume the first option but am I right - HELP!

If they are all exactly the same size I would cook them based on the size of one joint. Depends how many you are cooking for, where you are cooking it, and what your facilities are, but would it be cheaper to have one large joint. Good Luck.

Don't, whatever you do, add all the weights together! You'll end up cooking them all for about 8 hours and will end up with some very, very dry pork!