I have two 20lb prime rib cooking them for a business party tonight. I have them on large pans one thicker on bottom thinner on top each way the same amount. I am wondering do I cook per pound times 40 or per roast pound times 20? I need to serve at 6pm tonight. I have a probe in both.
How long to cook 2-20lb prime rib in one oven.............
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>>how long / how to . . .
you're likely to find / get several hundred conflicting "fool proof methods"
everything from turn the oven on for x minutes then off for y hours to put-it-in-the-dishwasher-on-the-heavy-soil-cycle.
when doing the "low&slow" method, be aware the meat starting temperature is a big factor.
straight out of the fridge? standing at room temp,,, for how long,,,,
personally I've settled on using 235'F; upping that about half way through to 245'F to render out some of the fat, then blasting it at the end using max broil to make a nice crust. that's just me - shooting "messenger me" is not requested.....
the rate at which heat is absorbed into the roast depends on (among other things....) the surface area....surface area is not a linear function of weight. just saying that x minutes per pound is not the best "blind" approach. as a guideline - yup, go with it - and keep a thermometer handy. also be aware, "bone in" takes longer than "off the bone" and "sliced off then stied back on the bone" falls somewhere in between, time-wise.
regrets I have no experience with stuff on the order of 20 lbs - I'm pretty much in the 3-4 bone / 10-12 lb range.
pre-ordered, dry aged 14 days, on the bone, not cut off the bone and retied....
for a nominal 10 lb size I plan on 4-6 hours seasoned & standing at room temp, four hours roast + rest time - keeping in mind that after two hours I check the internal temps every 30 minutes and raise/lower the oven temp as needed to finish on time.
a probe type thermometer with an external read out is a nifty tool; no got, just use a long probe dial/aka analog thermometer "in the same spot"