Expert: Steve Hanagan - 2/13/2008

Question
I bought 4 15lb prime rib roasts. I was estimating 3/4lb for each person. My 2 ovens run hot. If I plan to serve 50-55 people at 6:30p.m. at what temp. and how long do I need to cook the roasts for med. rare and can I put 2 roasts in each oven. They are just standard home-use ovens. Also if I slice before serving, will that stop the cooking process?

Answer
At 3/4 lb per person I assume these roasts are bone-in.  Otherwise, you have way too much for a normal gathering.

As far as cooking, 30 pounds of meat is a pretty large quantity to toss in a home oven, assuming they even fit, and time the cooking process.  As I mentioned in my previous answer, there are a lot of factors that influence the cooking time.  In this case, the volume of cold beef is the major factor.  You should plan to use the internal thermometer that I suggested.  It is very difficult to gauge the time, and the thermometer will at least assure the beef is cooked perfectly.  

Just as a rough estimate, using the formula of 11-12 minutes per pound with 20% added onto the time to account for the second roast in the ovens, I’d say you are looking at 3 hours to cook the two roasts to 133 degrees internal.  This is a ball park estimate, but should be good to around 15 minutes.  

Yes, you should slice the beef after resting it for 15 minutes in order to slow the cooking process down.  You will need to keep the slices separated for them to cool down quickly, but you probably won’t want to plate them immediately.  There will still be plenty of juice coming off of the slices, so plan to let them rest a couple of minutes as well before plating.

Working backwards from dinner at 6:30, here is what I would suggest time wise.  It allows a few minutes between carving and the Dinner time in the event the Roasts take a few minutes longer.

2:45  Roasts into the ovens at 325 degrees F.
5:45  Roasts out of the oven to rest
6:00  Carve the roasts
6:30  Dinner

Hope this helps.