Schneier on Security

Clive Robinson • December 22, 2007 3:31 AM

The Squid certainly appears to have a crush on the young lady next to it.

Mind you as it’s the festive season where traditional fare involves large stuffed creatures and the “bigger the better” is often seen as good especially when people trying to beat records or get into their local newspaper.

A thought occured,

At what size is an animal to large to stuff and roast (dry heat cooking) on purely health grounds?

As Bruce (probably) knows the larger the creature the lower the temprature at which you have to roast it for it to be cooked on the inside but not dryed/burnt beyond a crisp on the outside.

The lowest temprature at which protein is going to cook is a little over 40 centegrade (that’s why a human body with an internal temprature over 39 should be going down to the hospital pronto). Effectivly this means you can cook protien at 50 Centegrade.

However not all bacteria will die at 50C and the advice often seen is 80C.

For large slabs of herbivor meat bacteria is not normaly considered a problem as the middle of non spoiled meat generaly should never contain sufficient levels of bacteria to be harmfull even if eaten raw (think steak tar tar / tartare ground from 28day or more matured whole beef or European “air cure” hams and Salami etc hung for several months).

However when you stuff a carcus or roll meat around stuffing you are effectivly putting bacteria (in the stuffing) into the middle of the meat. As hung meat actualy has a very low moisture content stuffing is designed to have a very high moisture content which is supposed to help stop the meat drying out when roasting.

So stuffing is usually made of bacteria laden fruit or ground / force meat and some kind of moisture retaining high carbohydrate substance such as bread crumbs / oatmeal / rusk / rice. Unfortunatly the high moisture content and free carbohydrates in the stuffing is just what the bacteria need to breed and the only thing stoping them is that usually the stuffing is chilled below the temprature at which they will bread effectivly.

As the breeding rate of bateria is related to temprature and during cooking the temprature of the stuffing rises, at some point there will be a temprature window ideal for rapid breeding of bacteria in which their numbers will rise almost geometricaly (inverse half life if you will). The real limit on the bacterial multiplication will be how long the window is open for.

Now meat of all kinds is quite effective as an insulator and thermal energy takes quite some time to pass through it which means that the internal temprature of the meat will rise very slowly. Also the lower the external temprature used for roasting the longer the breeding time window is going to be.

So the question boils down to how thick does a piece of meat have to be and at how low a roasting temprature does it have to be for an acceptable level of bacteria in raw stuffing to breed to the point at which it is harmfull…

Any food scientists out there know the answer ?

Oh and enjoy that two hundredweght turkey they have specialy cooked down at your local eatery just to get in the local papers 😉