Food safety question for the scientists

Ah, Frank, you bring up a subject near and dear to my heart. There are even some tasks at which the brain appears to perform a rough form of numerical integration (i.e. calculus).

I may be wrong, but my guess is that if you give someone a word problem, they will give you the linear answer. I.e., "There are 1 million bacteria on a rack of ribs after 1 hour at room temperature, and 2 million after 2 hours. How many are there after 3 hours?" Scientists and mathematicians would probably (just from experience) spot the possible exponential, but I don't think the man on the street would. Another example: A 1-inch steak cooks in five minutes. How long does a 2-inch steak take to cook? Most people will tell you ten minutes. But heat transfer in a steak is diffusive, so actually the answer is more like 20 minutes.

I will listen to the podcast when I get a chance.

Walt

I may be wrong, but my guess is that if you give someone a word problem, they will give you the linear answer. I.e., "There are 1 million bacteria on a rack of ribs after 1 hour at room temperature, and 2 million after 2 hours. How many are there after 3 hours?" Scientists and mathematicians would probably (just from experience) spot the possible exponential, but I don't think the man on the street would. Another example: A 1-inch steak cooks in five minutes. How long does a 2-inch steak take to cook? Most people will tell you ten minutes. But heat transfer in a steak is diffusive, so actually the answer is more like 20 minutes.

Back when I was an undergrad, my advisor (a physical chemist) managed to convince me to continue my math education with a class in partial differential equations. I have never forgotten since then the heat equation and how freaking complicated its solution was.

Mark Lipton

[Jenise]

Walt said:

It's a range, where the middle is quite dangerous, and the edges much less so. In other words, if you can keep those ribs, Jenise, at 130F/54C, or cool them to 50F/10C, you'll be a lot better off.

Beautifully explained, Walt, this sure clarifies the situation. It also validates what I thought I learned in the long ago past, and which was the basis for my plan for last weekend, that letting the meat cool to cool room temperature was in fact better than holding the meat warmish.

And to Bill, re: [url]what the difference in terms of initial sterilization might be between ribs that are cooked quickly and hot over a BBQ, and ribs that are slowly smoked for 6 hours at temps of maybe 200 F. Would both be equally efficient at rendering the meat essentially sterile,[/url]

Don't overlook the effect of the salt and sugar components in the dry rubs, which Walt also mentioned. My ribs were in a heavy salt & sugar based rub for 18 hours prior to going on the smoker. I'm thinking that this preparation provided additional anti-bacterial protection vs. a rib that was only so treated just before hitting the fire.

Jenise, your point about the sugar reminded me of another factor. The preservative effects of sugar are all about concentration. Very sweet foods, like 20% or more sugar, are well-protected against bacteria. You can get something growing on the surface, but nothing on the inside. However, dilute sugary foods are an ideal bacteriological growth medium. As is raw meat, and interestingly potatoes. Basically anything with a neutral pH, sufficient nutrients, and a lack of salt, spice, and other preservatives.
One substance that is not prone to spoilage is mayonnaise! The main ingredients are fat (not prone to spoilage) and vinegar, which is an excellent preservative. The egg yolk is such a small portion that it can be ignored. You are far more likely to be sickened by the potatoes in the potato salad than the mayo.
I would be lax if I didn't mention another food that is seriously underestimated in its potential for food-born illness: rice. Yes, the white menace is suprisingly hazardous, because it's a good medium for bacterial growth and a lot of rice has botulinum in it. Yes, the bacteria that generates some of the most powerful neurtoxins and causes botulism. What's more, the usual rules about cooking killing bacteria don't apply as botulinum creates spores that can survive in boiling water! The toxin itself is destroyed by cooking, so in theory it's safe to eat reheated old rice, but I wouldn't risk it. I am pretty adventurous as far as food goes, I eat raw egg, sushi, ceviche from taquerias, etc., but I won't touch old rice. If it's been at room temp for more than a couple of hours, throw it out!

[Jenise]

Wow, speaking of food safety, coincidentally, I just now opened an email from an old FLDGer from way back. His name is Rob Keith and he was Australian, if that helps ring any bells for those who've been around awhile. Bob and I visited him and his delightful wife Jenny in Melbourne just over ten years ago. He was working on an invention of some kind and starting his own company. Although he fell off the board, I've heard from him every few years.

Anyway, today's email says that he's moved his company to the U.S. and that he and Jenny now live in Massachusetts. And what his company makes are the type of devices that monitor food temperature, for instance, during transportation! Here's a link to the website:


http://thermodata.us/

Thanks Walt for the excellent information. Not just great info, but presented in such a clear way. Bravo!

One substance that is not prone to spoilage is mayonnaise! The main ingredients are fat (not prone to spoilage) and vinegar, which is an excellent preservative. The egg yolk is such a small portion that it can be ignored. You are far more likely to be sickened by the potatoes in the potato salad than the mayo.

Yes, on the wall next to my desk* is an enlarged reprint of an old article (Ive had for at least 15 years) entitled "on second thought, don't hold the mayo" Not only is mayo not prone to spoilage, if anything the acid (ph 3. inhibits bacteria. A piece of meat with mayo is (very slightly) less prone to spoilage that without. As Walt notes, the article mentions the worst is near body temp- article says room temp over 85°F that one hour is probably safety limit.

*I have volunteers every year who say "it's hot I'll leave off the mayo." But I explain the meat in sandwich (or pasta in salad) will spoil before the mayo. The main thing is keeping cold (or hot).

damn sql error won't let me edit. That is 3.8 ph

Wow, speaking of food safety, coincidentally, I just now opened an email from an old FLDGer from way back. His name is Rob Keith and he was Australian, if that helps ring any bells for those who've been around awhile. Bob and I visited him and his delightful wife Jenny in Melbourne just over ten years ago. He was working on an invention of some kind and starting his own company. Although he fell off the board, I've heard from him every few years.

Anyway, today's email says that he's moved his company to the U.S. and that he and Jenny now live in Massachusetts. And what his company makes are the type of devices that monitor food temperature, for instance, during transportation! Here's a link to the website:


http://thermodata.us/

Wow - there's a name I haven't heard in a long time! Glad to hear things are going well for him.

http://www.slate.com/id/2300787

Yes, Dale, that's an excellent one. Explains scientifically why you're not likely to get sick from something in the fridge that has obviously soured, while something that's been sitting at room temperature that tastes delicious can lay you down low.

So Walter, I'm interested in seeing you post in the Pie topic.

Which kind of pie is most likely to kill us?!?

Actually in grad school I had a class in forensics, and evidently it has occurred to more than one disgruntled housewife that she could sneak some ethylene glycol anti-freeze into a cherry pie, without significantly altering the taste or the gooey texture. It's interesting to think about a CSI type having to reverse engineer something like that and prove that the widow did it.