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Timing for HUGE Prime Rib via Joule

David_Garrett_438542

Hi. I recently received my Joule and am loving it. I have a question about cooking times. I'm hosting xmas eve and have 25 people coming. I've ordered one 5 rib prime rib, and one 4 rib. Both are dry aged. It should be about 20-22 lbs in total. I plan to follow the Herb Crusted Rib Roast recipe. I want to get the meat to medium temp (136 degrees). In the Joule app, it only gives two options for how thick the roast is - 4-5 in or 5-6 in. My two rib roasts will obviously be much bigger. Question for the ChefSteps team/community, how long should I sous vide my two rib roasts? Or do you recommend that I cut into 5-6 inch pieces? Many thanks in advance for the help.

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Comments

meyer8863

Greetings David, and interesting question. I am going to attempt to answer, but keep in mind I am speaking as a physicist, not an extraordinarily experienced cook.

TL;DR

I would cook at the same temperature, for not TOO much longer than the Joule recipe recommends. I would increase the minimum cook time by 1-2 hours, tops.

When calculating heat transfer and the time it will take to heat something up in a water bath, one of the first things to consider is the shape. A 4-5 inch roast tends to be as thick as it is wide. To make the math easy, we assume the shape of a sphere. When you increase the number of ribs, the thickness increases, but the length and width of the cross-section does not. This creates more of a log/cylindrical shape. The 5-6 inch rib roast will have a more cylindrical shape than the "round" 4-5 inch roast. So when calculating cook times, we assume a cylinder shape. In this REHEATING post, you will see how the times change between a sphere and a cylinder. What you see with the cylinder time table, is that length is not really a factor...only the cross-sectional thickness. Because of that, I wouldn't adjust the original recipe for a 5-6 inch roast too much, since they are already assuming the cylindrical shape.

I would also check out Douglas Baldwins time table HERE.

fisher23

My opinion go for 9-10 hours, getting the heat to the core is an exponential math problem not just twice as thick so twice the time, more like three times. I understand @Michael_Meyer_123524's reasoning and it makes total sense, I always err on the side of caution, especially when I am having guests. When I am unsure I use a prob thermocouple inserted through the bag with sous vide tape (closed cell foam tape maintains the integrity of the bag) to check core temperature. You can do the same with a thermometer and if the core isn't up to temp you can always put it back in the bath. At least if you go the 9-10 hours you know it will done when your guests are ready to eat, and additional time won't harm your roast. I have not done one that large so this is a my best guess.

David_Garrett_438542

Thank you both very much! Happy holidays

fisher23

And Happy Holidays to you and yours too.