Thermal profiles of domestically baked leg-of-lamb roasts and implications for microbiological safety

The measurement of the effectiveness of cooking in the real world has received little attention in the scientific literature. In this study the core temperatures of 16 leg-of-lamb roasts were measured during baking in 14 electric or gas-fired domestic ovens in order to assess the adequacy of cooking relative to recommendations of food authorities to minimise foodborne illness due to microorganisms. The mass of the roasts was 1.80 ± 0.33 kg (mean ± s.d.). The intended extent of cooking indicated by volunteer cooks who were selected from a range of cultural backgrounds ranged from rare to well done, with most preferring greater than medium rare, but the actual degree of doneness achieved was slightly more than intended. One roast was unevenly cooked, with parts well done and other parts medium rare. Ovens reached peak temperature over a variable period ranging from 5 to 25 min. However, there was substantial variation between the oven set temperature and the actual maximum oven temperature recorded. Only five of 14 ovens provided an actual maximum temperature within 10 °C of the set temperature and some were as much as 50 °C below the set temperature. Peak temperatures at the core of the majority of roasts were attained after about 1.5–2.5 h. The maximum core temperatures recorded among roasts ranged from 59.6 °C to 98.3 °C; three roasts had maximum core temperatures less than 70 °C. The least well-cooked roast reached 59.6 °C at one probe site and 65.9 °C at the other. The variables observed in this study support recommendations for use of meat thermometers during baking of red meat and should stimulate further evaluation of domestic cooking practices.