The inside of a whole muscle is almost sterile and the bacteria sit on the surface, so what a whole cut needs heated through is the outer layer.Inside a whole muscle the interior was almost sterile — sealed inside the living animal. Contamination happens on the surface. For a whole cut, what needs heating through is the outer layer; by the time the centre hits the number, the outside has already been past it.
2 · Grinding mixes the surface into the centre
Grinding mixes the original surface into the centre, spreading bacteria through the whole mass, so every spot has to meet the mark on its own.What grinding does is specific: it mixes the original surface into the centre. Bacteria that sat only on the outside now run through the whole mass. The advantage of the surface cooking first disappears — every spot may have been the original surface, and every spot has to meet the mark.
3 · Rest is time spent at temperature
Inactivation keeps going while the meat stays at temperature, so the reading plus the rest minutes make up the whole rule.Inactivation does not finish in the instant a temperature is reached. It keeps going while the meat stays at temperature. After you take it off the heat, heat stored outside keeps walking inward. The reading is the ticket; the rest minutes are time in the seat.
4 · Colour is a proxy, not the quantity
Pork has less myoglobin than beef or lamb and looks pale before it reaches temperature, so doneness is read on a thermometer, not judged by colour.Pork already has less myoglobin than beef or lamb, so it looks pale before it has reached temperature. Judging doneness by colour is more misleading here. A thermometer reads the quantity you actually care about. Cook to that line and trichinella is handled in the same pass — it is not a reason to add extra degrees.
Mechanism
Pork — surface versus ground
On a whole cut the bacteria sit on the surface; grinding mixes that surface in.