Timing roast lamb, some rules of thumb

In my post on Hugh Fearnley-Whittingstall’s Roast breast of lamb with fennel salt I wanted to provide a rule of thumb for timing roast lamb, but the more examples I looked at, the more hesitant I became to provide something definitive.

In all of the examples I have seen, the cooking time is calculated based on the weight of the lamb, which is usually given in 1lb (450g) or 500g increments. But in each case both the timing and temperature varied, for example: 

• A Delicious magazine article on the subject suggested an initial blast at 230C for 15 minutes for larger joints, then 13 minutes per 500g for rare, 18 minutes per 500g for medium and 20-22 minutes per 500g for well done at 180C. For smaller joints they suggest roasting at the higher heat the whole time.
• An article in The Sunday Times suggests 20 minutes per 450g plus 20 minutes, with the first 20 minutes at 220C and the remaining time at 180C.
• Delia Smith suggests cooking the lamb at a consistent temperature (gas mark 5/375F/190C) for 30 minutes per lb (450g), but adds that those who prefer their lamb quite pink should give it 30 minutes less cooking time. She also suggests inserting a skewer to judge how rare it is based on colour of the juice that runs out.
• The United States Department of Agriculture provides the most comprehensive table I have seen, providing  different guidelines  according to the cut of lamb, size, cooking method and providing the optimum internal temperature and different cooking times depending on your preference for medium rare, medium or well done. 

As you can see, timing and temperature are not the only variables; the type of oven (fan, gas, electric), the joint you are using, whether you cook it from room temperature, how you like your meat, and whether you use a consistent heat or lower the temperature after an initial blast will all affect the outcome.

I have an electric oven. The element is on the top, which is not great when you consider that heat rises. It also tends to work like a grill, burning the top of almost everything before the middle has even begun to cook.  In addition, the thermostat is broken so I am only able to cook things at 200C plus, unless I open the oven door at regular intervals, in which case I can keep it down to about 180C. Bearing these extreme conditions in mind, I have found that the following rough guideline works for me: 20 minutes standard cooking time plus 20 minutes per 500g, with the first 20 minutes at 220C and the rest at 180C. I would suggest that you experiment with the different rules of thumb provided in the above links and find something that works for you.

I would be interested to hear your thoughts on the subject in the comments.

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[jacynfrie]

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[jacynfrie]

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