Roasting beef: 50mins per 500g, but what about 2x500g?

NVP

NVP

NVP

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Quick help please if you guys would be so kind.

The recipe states to cook the beef for 50mins per 500g, so if i had a single 1kg slab obviously it would be in for 100 mins - but what if I have 2 seperate 500g joints in the same roasting pot, I just cook them for 50 mins total right?

I'm finding conflicting information :confused:

Cooking times ought to be very similar because the oven radiates (a lot of) heat. Surface area doesn't generally enter into it unless you're cooking stovetop, in the oven it's volume that matters.
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The time that it takes to roast something is based on the time it takes to get the internal temperature to "cooked" depending on how you like it. The bigger the roast, the longer it takes for the internal temperature to reach the correct temperature. It is based on the distance from the outside to the inside on a roast, so two 3 pound roasts will take a good bit less time than one 6 pound roast. By contrast, if you have a very flat thin 6 pound piece of meat, it will take less time to cook than the 3 pounders.
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And then I found this:

Suppose we have two roasts with exactly the same combination of identical tissues, and the same shape except that the one is a scaled (blown up) version of the other. Let's weigh both roasts and compute the ratio between the two weights; let's call that ratio r. Suppose furthermore that the roasts have the same starting temperature, and we will cook both until they have both reached some given (higher) temperature at their centre. What can we say about the times that both roasts need to cook for?

The answer is that under these assumptions, the bigger roast will need r^(2/3) times as long as the smaller one.

So, assuming each small roast (700 and 950 grams) has the same shape as the big one that the recipe writers used (let's say 1750 grams), for the 950 gram roast you'd expect to use (950 / 1750)^(2/3) = 0.665 or about two-thirds of the cooking time, and for the 700 gram one you'd expect to use (700 / 1750)^(2/3) = 0.543 or just over half of the cooking time. In particular, for the 950 gram roast, you should expect to roast it at 200C for 20 minutes, then turn down to 180 and roast for around 0.665 * 1750 / 450 * 12.5 = 32 minutes more. (1750 / 450 * 12.5 = 49 minutes is the average time they would recommend for the 1750 gram roast, and we're using that as the base for comparing our 950 gram roast against.) Then check with your thermometer!
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I think I should buy a meat thermometer! But for some quick advice for today's Sunday lunch, what are people's opinions?

I'm thinking if I have them spaced properly in the dish then I should be cooking at the single weights time and not for double? So simply 50mins...? :(

Cheers :)
 
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Cook it for the length of time you would cook 1 x 500g.

You should definitely get a meat thermometer for next time though :)

Before I got a sous vide I used to cook by setting the oven to the exact temperature I wanted the meat to hit and then left it in there for several hours. If you can be precise with your oven temperature it will achieve better results.
 
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Ah, clever little trick :) thanks. Cheers for the advice, meat thermometer will be ordered shortly but I usually can tell from a little squeeze... Usually, I've had the occasional mistake :o
 
FrenchTart said:
Before I got a sous vide I used to cook by setting the oven to the exact temperature I wanted the meat to hit and then left it in there for several hours. If you can be precise with your oven temperature it will achieve better results.
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Surely it must have taken days to cook at those temperatures?
I cook my beef to about 60c, so you'd put your oven to 60c?

I use this website as a guide and cook it to rare, it works really well.
 
chipperhead said:
Surely it must have taken days to cook at those temperatures?
I cook my beef to about 60c, so you'd put your oven to 60c?

I use this website as a guide and cook it to rare, it works really well.
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Nope. It took maybe 6 or 8 hours from memory. One of the advantages of this is that you can leave it in for longer without it negatively impacting the end result. Just stick it on in the morning and then take if out when you need to serve or when you need the oven for something else.

Thermapens are great. I've been meaning to upgrade to one from my current temperature probe for a while.
 
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FrenchTart said:
Before I got a sous vide I used to cook by setting the oven to the exact temperature I wanted the meat to hit and then left it in there for several hours. If you can be precise with your oven temperature it will achieve better results.
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This is an excellent tip. Unfortunately you need an oven with decent control because there is only a few degrees core temp between rare and well done. I do not have such an oven :(
 
Lt_Red said:
This is an excellent tip. Unfortunately you need an oven with decent control because there is only a few degrees core temp between rare and well done. I do not have such an oven :(
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My oven has literally no markings on the temperature dial (actually, thinking about it you can still just about make out the 200C notch) so I had to leave a temp probe in there and try to play with the temperature for about 30-60 minutes to try and get it to something decent. Even then, the temp would vary by up to 5C. I eventually would set the oven so that the peak of the temperature was the target temperature for the meat. After it had been on for an hour or two the peaks and troughs levelled out somewhat.

Reading the above I can see how it might appear to be a massive amount of hassle and the first two times it was if I'm honest...but after I got used to how my oven works it became quite a simple process and I could guess the setting I had to choose fairly accurately without so much fuss.
 
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