I have read this: Lamb rack cooked under 130°F / 54.4ºC should not be cooked longer than two-and-a-half hours at a time for food safety reasons. My question is: what is this safety reason? For higher temperatures is it allowed to overcook?
Killing bacteria at temps below 130F is kind of tricky. At 131F it takes almost 2 hours to kill off everything. As temperatures increase, the kill time goes down.
The theory behind this is that bacteria can still be multiplying at 130ºF, but the truth is that there is a built-in buffer zone to the fail-proof USDA regulations to REALLY ensure people do not get sick. For a very scientific explanation, PhD in Sous Vide Douglas Baldwin states in one of my favorite articles to quote:
“You were probably taught that there’s a “danger zone” between 4.4◦C/40◦F and 60◦C/140◦F. These temperatures aren’t quite right: it’s well known that food pathogens can only multiply between −1.3◦C/29.7◦F and 52.3◦C/126.1◦F, while spoilage bacteria begin multiplying at −5◦C/23◦F (Snyder, 2006; Juneja et al., 1999; FDA, 2011). (Johnson et al. (1983) reported that Bacillus cereus could multiply at 55◦C/131◦F, but no one else has demonstrated growth at this temperature and so C. perfringens is used instead.) Moreover, contrary to popular belief, food pathogens and toxins cannot be seen, smelt, or tasted.
So why were you taught that food pathogens don’t multiplying below 4.4◦C/40◦F and grow all the way up to 60◦C/140◦F? Because it takes days for food pathogens to grow to a dangerous level at 4.4◦C/40◦F (FDA, 2011) and it takes many hours for food to be made safe at just above 52.3◦C/126.1◦F — compared with only about 12 minutes (for meat) (FDA, 2009, 3-401.11.B.2) and 35 minutes (for poultry) (FSIS, 2005) to be made safe (for immuno-compromised people) when the coldest part is at 60◦C/140◦F.”
Translation - it is not dangerous for you to cook your lamb for over 4 hours at 130ºF!