Help! How long do you cook a really large roast?
Major challenge this year. I have to serve Christmas dinner out of one sister's impossible kitchen -- It has an ancient, tiny oven and two working burners.
I'm making porchettas. I have two 10 lb. rolled pork shoulders crammed into one roasting pan. Amazingly, they do not touch. There's about an inch between them.
I researched cooking times last night, and they were alarming. My understanding is that Porchetta should be cooked pretty low and slow to a pretty high internal temperature. Research suggested that, at 325, this could take 10-12 hours for a 20 lb. roast.
This leaves me with questions -- Will my non-touching roasts behave like one 20 lb. roast, or two 10-lb. roasts, or something in between? Would I be better off separating them and taking them to the house of sister-with-two-ovens and running back and fourth all day to tend to them? The rest of the dinner is fully prepped, so I don't necessarily want to sit around sister-one-oven's kitchen for 12 hours on Christmas.
Thanks in advance to anyone who might have some 11th hour advice on Christmas Eve...
Your timing should be based on a ten-pound roast, but build in an extra hour or so since they are close together. Turn them back and forth a few times while roasting, so the facing sides are on the outside. Use a meat thermometer to monitor the temps. If the first time you check, you find that the inner sides are close to the temp of the outer sides, you won't have to swap the roasts around more than once or twice. But it sounds like they may be flush up against the sides of the roasting pan and if that's the case, those parts will get hotter than the inner sides.
It's all about volume and surface area, so the two (Can really be any number) roasts will behave more like a single roast (slightly longer still). So, the good news is that your cooking time will be much shorter than what you're expecting. The bad news is that you really need to be careful with the seasoning concentration in the liquid; the one risk I see here is it being over-seasoned as you baste and add stock to the crowded pan. Also, you may want to take both temperatures, since they will cook at slightly different rates; but that's a minor thing since you took care into cutting/shaping them similarly.
My only addition to the advice you've received is to bring an oven thermometer if none is already there.
My recommendation is for you to reduce your roasting temperature to 225-250* and expect 6-8 hours, depending on how thick the roll is and. With low and slow temperature roasting, there is very little need to monitor before you reach the approximate temperature of 170*, which is need to slice the Porchetta. Many like more tender meat and for the collagen to melt, which begins at 190*
If you intend to roast @ the 325* setting, I suspect you could reduce the expected roasting time to be 4-6 hours. Depending on the calibration and efficiency of the small oven you are using, second roasts in the the same ovens, the general rule in commercial kitchen is to add 30 minutes more for the second roast.....however, I could agree in this case it would not be unusual for this to exceed 30 minutes and be closer to 60, surmised due to limited air flow.
Depending on what time you plan to serve your dinner, consider putting the roasts in the oven At midnight and roast at a lower temperature of 200* for about 12 hours. That's what I do with Bone In Picnic shoulders or Fresh Hams. You cannot dry out meats when you roast at low temperature and there is a high margin for any errors.