Food safety question

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Bewildered
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Food safety question

Post by Bewildered » Thu Oct 06, 2022 10:59 am

Standard food safety advice seems to be that if you leave meat out of the fridge for 2-4 hours it’s unsafe to eat.

I am wondering if anyone knows or can find more detailed science on the risks and what they depend on. Obviously the risk should vary with actual temperature (if you reliably know it) and it should get riskier as time progresses are there estimates of the risk vs time. Also just curious what kind of risk is acceptable. If I left food out for exactly two hours every day before eating would they expect I never once get sick over the course of my whole life?

IvanV
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Re: Food safety question

Post by IvanV » Thu Oct 06, 2022 12:20 pm

You go to a meat market in a traditional country, and the meat is just hanging up there on hooks in the ambient temperature for sale all morning. I think raw meat can survive being at ambient temperature for quite some time if you are going to cook it sufficiently to pasteurise it, in the great majority of cases.

There are some things that grow that give up toxins as they operate, and leave the food still poisoned despite the cooking pasteurising them. Botulism, for example. The blue mould that grows on cooked rice. So there are some risks. But we can see from practices such as traditional meat markets that they are relatively low risks if you are sensible about it.

My sister used to go out with a food hygiene inspector. He told me about the worst food poisoning problem on his watch. A Christmas dinner cooked for an old folks residence. It was cooked the day before. Then it wasn't chilled fast enough. Big turkeys took a long time to lose their heat stored at ambient temperature, and left whole out of the oven. Bacteria etc grew at an ideal temperature for rapid replication. Then it wasn't heated up enough to repasteurise it. His point was that the biggest danger period is cooling down after cooking. The items can spend an extended period at ideal temps for bacteria propagation if not cooled fast enough.

Pasteurising is a powerful thing. When cycling in S America, I often wild-camped and used surface water sources to cook my meal, and fill my water bottle. I always heated the water sufficiently to pasteurise it. I never had any problem with it with boiled water. Even in a few couple of cases where I could be see or smell evidence of some sewage contamination to the river.

KAJ
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Re: Food safety question

Post by KAJ » Thu Oct 06, 2022 8:48 pm

Before retirement I spent >40 years as a food scientist, the last decade or two modelling growth, survival and death of pathogens, so I can get boring on this. But partial advice is probably worse than none, and I haven't time or resources to be complete, so take care, don't depend on what I say, and satisfy yourself before taking action based on anything I say.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
Standard food safety advice seems to be that if you leave meat out of the fridge for 2-4 hours it’s unsafe to eat.
I'm not aware of such "Standard food safety advice", and IABMCTT, but it's not a bad rule of thumb. It could perhaps be justified thus...

Food microbial growth in constant conditions often follows an approximately sigmoidal growth curve with three phases:
* Lag: count v. time approximately constant
* Log: (or exponential) log(count) v. time approximately straight line increase
* Stationary: count v. time approximately constant
A fourth phase, rarely relevant to food pathogens, and rarely considered is:
* Death (or decline): count v. time decreases

Safe storage time is often considered to be limited to the lag time. Under optimal (for the pathogen!) growth conditions lag time is often of the order of hours, so that rule is probably safe.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
I am wondering if anyone knows or can find more detailed science on the risks and what they depend on. Obviously the risk should vary with actual temperature (if you reliably know it) and it should get riskier as time progresses are there estimates of the risk vs time.
Lag time and growth rate depend on many factors. As well as the nature and previous history of the microbiome, environmental factors have great influence. The most important of the latter are often (usually?) temperature, pH, and water activity - any one of which can be controlled to effectively stop microbial development.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
Also just curious what kind of risk is acceptable. If I left food out for exactly two hours every day before eating would they expect I never once get sick over the course of my whole life?
Now things get complicated.

In my terminology (similar to that of Whiting) the sigmoidal curve modelling growth under constant conditions was a "primary model", which usually had four parameters, one reflecting lag time. Sigmoidal models can be difficult to fit. When I retired there were a number of sigmoidal primary models in use; IMHO (not universally shared) there is little practical difference between them with respect to food safety.

The models reflecting the dependence of the primary parameters on conditions (including temperature) were "secondary models". When I retired there was little agreement and less justification in the choice of secondary models. Quadratic response surfaces were quite common, and usually my preferred choice.

Both of these model types were restricted to constant conditions. You postulate changing conditions (temperature). In my terminology this would have required "dynamic modelling". (The commonly used Baranyi model is often described as dynamic, but in my terminology it is a primary model).

The lag time is usually considered as reflecting the organisms adaptation to conditions. If the conditions change very little then one would expect little need for re-adaptation, so little extension of lag time. A slow change could be considered as a sequence of very small changes, so little extension of lag time. But we know that large, rapid changes do extend lag time. Quantifying these considerations is not easy, at the time I retired I was actively working on such dynamic modelling. I am not aware of any useful dynamic models.

IMHO the changes you postulate would be considered as slow and small, that is the total time out of the fridge should be considered the determinant of safety.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
You go to a meat market in a traditional country, and the meat is just hanging up there on hooks in the ambient temperature for sale all morning. I think raw meat can survive being at ambient temperature for quite some time if you are going to cook it sufficiently to pasteurise it, in the great majority of cases.
As I said above, IABMCTT. Whole meat is usually effectively sterile in the interior (but not always, e.g. "meat needling"). Roasting, grilling, or frying get the outside very hot - hot enough to kill most pathogens. Minced (aka ground) meat can be much more risky.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
There are some things that grow that give up toxins as they operate, and leave the food still poisoned despite the cooking pasteurising them. Botulism, for example. The blue mould that grows on cooked rice. So there are some risks. But we can see from practices such as traditional meat markets that they are relatively low risks if you are sensible about it.

My sister used to go out with a food hygiene inspector. He told me about the worst food poisoning problem on his watch. A Christmas dinner cooked for an old folks residence. It was cooked the day before. Then it wasn't chilled fast enough. Big turkeys took a long time to lose their heat stored at ambient temperature, and left whole out of the oven. Bacteria etc grew at an ideal temperature for rapid replication. Then it wasn't heated up enough to repasteurise it. His point was that the biggest danger period is cooling down after cooking. The items can spend an extended period at ideal temps for bacteria propagation if not cooled fast enough.
You're confusing Clostridium botulinum and bacillus cereus.

C.botulinum only produces toxin under anaerobic conditions. Both the vegetative cells and the toxin are heat labile and easily destroyed by cooking. It is the spores which are heat resistant.

B.cereus produces a toxin which is heat resistant and has led to many poisonings, especially from cooked rice.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
Pasteurising is a powerful thing. When cycling in S America, I often wild-camped and used surface water sources to cook my meal, and fill my water bottle. I always heated the water sufficiently to pasteurise it. I never had any problem with it with boiled water. Even in a few couple of cases where I could be see or smell evidence of some sewage contamination to the river.
You should distinguish between pasteurisation and [commercial] sterilisation. Pasteurisation is adequate in many (most?) circumstances. but some circumstances (pathogens) need more - e.g. cryptosporidium.

KAJ
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Location: UK

Re: Food safety question

Post by KAJ » Thu Oct 06, 2022 10:00 pm

Correction to my last sentence above, cryptosporidium is killed by usual pasteurisation treatments - it's chemical treatment that it survives.

Bewildered
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Re: Food safety question

Post by Bewildered » Fri Oct 07, 2022 12:40 pm

KAJ wrote:
Thu Oct 06, 2022 8:48 pm
Before retirement I spent >40 years as a food scientist, the last decade or two modelling growth, survival and death of pathogens, so I can get boring on this. But partial advice is probably worse than none, and I haven't time or resources to be complete, so take care, don't depend on what I say, and satisfy yourself before taking action based on anything I say.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
Standard food safety advice seems to be that if you leave meat out of the fridge for 2-4 hours it’s unsafe to eat.
I'm not aware of such "Standard food safety advice", and IABMCTT, but it's not a bad rule of thumb. It could perhaps be justified thus...

Food microbial growth in constant conditions often follows an approximately sigmoidal growth curve with three phases:
* Lag: count v. time approximately constant
* Log: (or exponential) log(count) v. time approximately straight line increase
* Stationary: count v. time approximately constant
A fourth phase, rarely relevant to food pathogens, and rarely considered is:
* Death (or decline): count v. time decreases

Safe storage time is often considered to be limited to the lag time. Under optimal (for the pathogen!) growth conditions lag time is often of the order of hours, so that rule is probably safe.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
I am wondering if anyone knows or can find more detailed science on the risks and what they depend on. Obviously the risk should vary with actual temperature (if you reliably know it) and it should get riskier as time progresses are there estimates of the risk vs time.
Lag time and growth rate depend on many factors. As well as the nature and previous history of the microbiome, environmental factors have great influence. The most important of the latter are often (usually?) temperature, pH, and water activity - any one of which can be controlled to effectively stop microbial development.
Bewildered wrote:
Thu Oct 06, 2022 10:59 am
Also just curious what kind of risk is acceptable. If I left food out for exactly two hours every day before eating would they expect I never once get sick over the course of my whole life?
Now things get complicated.

In my terminology (similar to that of Whiting) the sigmoidal curve modelling growth under constant conditions was a "primary model", which usually had four parameters, one reflecting lag time. Sigmoidal models can be difficult to fit. When I retired there were a number of sigmoidal primary models in use; IMHO (not universally shared) there is little practical difference between them with respect to food safety.

The models reflecting the dependence of the primary parameters on conditions (including temperature) were "secondary models". When I retired there was little agreement and less justification in the choice of secondary models. Quadratic response surfaces were quite common, and usually my preferred choice.

Both of these model types were restricted to constant conditions. You postulate changing conditions (temperature). In my terminology this would have required "dynamic modelling". (The commonly used Baranyi model is often described as dynamic, but in my terminology it is a primary model).

The lag time is usually considered as reflecting the organisms adaptation to conditions. If the conditions change very little then one would expect little need for re-adaptation, so little extension of lag time. A slow change could be considered as a sequence of very small changes, so little extension of lag time. But we know that large, rapid changes do extend lag time. Quantifying these considerations is not easy, at the time I retired I was actively working on such dynamic modelling. I am not aware of any useful dynamic models.

IMHO the changes you postulate would be considered as slow and small, that is the total time out of the fridge should be considered the determinant of safety.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
You go to a meat market in a traditional country, and the meat is just hanging up there on hooks in the ambient temperature for sale all morning. I think raw meat can survive being at ambient temperature for quite some time if you are going to cook it sufficiently to pasteurise it, in the great majority of cases.
As I said above, IABMCTT. Whole meat is usually effectively sterile in the interior (but not always, e.g. "meat needling"). Roasting, grilling, or frying get the outside very hot - hot enough to kill most pathogens. Minced (aka ground) meat can be much more risky.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
There are some things that grow that give up toxins as they operate, and leave the food still poisoned despite the cooking pasteurising them. Botulism, for example. The blue mould that grows on cooked rice. So there are some risks. But we can see from practices such as traditional meat markets that they are relatively low risks if you are sensible about it.

My sister used to go out with a food hygiene inspector. He told me about the worst food poisoning problem on his watch. A Christmas dinner cooked for an old folks residence. It was cooked the day before. Then it wasn't chilled fast enough. Big turkeys took a long time to lose their heat stored at ambient temperature, and left whole out of the oven. Bacteria etc grew at an ideal temperature for rapid replication. Then it wasn't heated up enough to repasteurise it. His point was that the biggest danger period is cooling down after cooking. The items can spend an extended period at ideal temps for bacteria propagation if not cooled fast enough.
You're confusing Clostridium botulinum and bacillus cereus.

C.botulinum only produces toxin under anaerobic conditions. Both the vegetative cells and the toxin are heat labile and easily destroyed by cooking. It is the spores which are heat resistant.

B.cereus produces a toxin which is heat resistant and has led to many poisonings, especially from cooked rice.
IvanV wrote:
Thu Oct 06, 2022 12:20 pm
Pasteurising is a powerful thing. When cycling in S America, I often wild-camped and used surface water sources to cook my meal, and fill my water bottle. I always heated the water sufficiently to pasteurise it. I never had any problem with it with boiled water. Even in a few couple of cases where I could be see or smell evidence of some sewage contamination to the river.
You should distinguish between pasteurisation and [commercial] sterilisation. Pasteurisation is adequate in many (most?) circumstances. but some circumstances (pathogens) need more - e.g. cryptosporidium.
Thanks this is very helpful and not at all boring! Let me digest it more and read the links etc and then maybe I’ll ask some more questions.

KAJ
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Location: UK

Re: Food safety question

Post by KAJ » Fri Oct 07, 2022 2:59 pm

Those links are very old and specialised to modelling, not really recommended reading.

If you want some informative microbiological reading I highly recommend the Bad Bug Book. For food safety guidance you could do worse than start at FoodSafety.gov.

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