20 Lbs Prime Rib Roast - Boneless

This will be my first attempt to Sous Vide a Prime Rib Roast.
Last year I did it on the BBQ rotisserie, and low & slow smoked another.
I think Sous Vide will give me the best control.

20 lbs Boneless Prime Rib Roast for Xmas.
I have a nice 5 gallon container for the water bath.
I’m going to cut it in half to make it more manageable in the bath.
So really two 10 Lbs roasts at the same time.
I plan to run the water temp at 133 degree.
What should I run as a cooking time in the bath before Searing?
Your suggestions please.

Agreed that SV provides you with optimal control of your cooking.

However, control should not be your only decision factor in making the choice of cooking technique you will use. Two 10 Lb. roasts are not appropriate learning items with a new technique.

Competent cooks always start with a detailed plan based on their knowledge and experience. You are economical with some critical decision factors that limit others’ input here beyond some general recommendations.

Top of list is thickness. The roasts may be tied as cut from the bones, or the deckle meat may have been removed for uniformity and the trimmed fat cap replaced and tied. That can make a significant difference to your control. You may wish to measure the roasts’ thickness to be better able to plan their cook times.

The time range for the roasts you are comtemplating is 6 to 12 hours with the other critical variables being pasture or feed-lot raised, aging, and grade.

First time for everything.
It’s a COSTCO Prime grade boneless rib roast.
Trussed up the diameter of each is about 5.5-6 inches
length is 10 inches each
Costco doesn’t specify grass fed or grain finished.

Think about what has to take place in the SV cooking process. Low temperature heat from the water bath has to penetrate your roasts’ thickness. At 133F heat difuses relatively slowly into meat. Not at all as quickly the heat of your grill or smoker.

Cooks calculate SV heating time using meat’s thickness. Length isn’t considered because heat always takes the shortest path (thickness) to the core achieving temperature equilibrium, That’s the point at which meat can be thought of as being just-cooked. After that length of time cooks often add more resulting in aditional tenderness. How much more is up to the cook to decide based on personal preferance and experience.

There’s a particular challenge in SV cooking roasts the size of yours, the length of time can be quite long before achieving temperature equilibrium. You may wish to consult Douglas Baldwin’s work to gain a more complete understanding of the food safety challenge.


Costco sells mass produced beef that’s been moderately aged. Thus i would consider no less than a 10 to 12 hour cook.

If you can afford the time and effort cook one roast as you plan and judging from the outcome adjust the second roast’s cooking time if necessary.

Do well.

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chatnoir has given excellent advice.
Having done the roast you are attempting (7lb) I used a temp of 138’ and while the roast was rare and tender I was very disappointed in the texture of the fat. For me, the fat being gelatinized inside and crispy outside is what makes this roast the go to Christmas beast. SVing at the rare temps will not get you there and higher temps make the meat too done for my taste.
My solution was to SV the roast at 134 ( forget how long ) the day before, chilling well in the fridge overnight and then putting it in the Kamodo on a hot fire and turning it every ten minutes or so for about an hour to get the roasted crispy crust and the heat to penetrate just inside so the lovely fatty bits were not hard as lard but the meat is still pink and juicy.
FYI, I never did the queen of roasts SV again, too much prep work as opposed to a good KK fire and a good wi fi thermometer. Also gravy :slight_smile:
Hope your meal was great, Hope to hear back how it went.
Thanks for posting,

Fat will not render well at sous vide temperatures. That is where your searing technique of choice comes into play. It is well worth searing any fat cap before you concentrate on searing the exposed meat. Then come back to the fat cap again just before you finish. The fat will help insulate the meat from getting further cooking. Insulating is basically what fat does when the animal is still on the hoof, afterall.