Take it with a pinch, no, a bag of salt!

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Food Australia, who should know better, published an article earlier this year titled "Contaminated reusable grocery bags pose health risks" (63 (5) - May 2011). It was based on an article by Gerba & Sinclair entitled "Assessment of the Potential for Cross Contamination of Food Products by reusable Shopping Bags". You can download the full article here.

The article suggests bacteria, including E. coli, flourish in the green bags.

And the are probably right. The same way bacteria can flourish in pretty much any environment. Because bacteria is IN the environment. If they had done their survey by swabbing the jeans of the shoppers rather than the bags, they would have got similar results.

And as for soaking the shopping bags in meat juices and leaving them in a car boot (trunk) for two hours - well, duh!, of course bacteria levels will increase.

It was all a bit odd and I had a niggling suspicion, which is why I chased down the original article rather than relying on the summary in Food Australia. My suspicion was confirmed in the following line:

"The authors would like to acknowledge and thank the American Chemistry Council for providing funding to support this study."

So, the American Chemistry Council, a body that includes all the plastic (bag) manufacturers of America in its ranks funded the research.

Doesn't mean it's wrong but there are flashing lights all over it!
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Smells dead, must be dead.

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Chairman Bill asked: "How about trassi? I've heard some hideous stories about it, although I've eaten plenty of it in my time (both as a Dutchman and when in Indonesia/Malaysia)"

This is an amazing fermented dried shrimp paste that smells awful but tastes wonderful.

The big thing is that this is a traditional food; a pretty reliable sign of a good track record for safety.

And the traditional way of cooking it is to stir-fry in a very hot wok. This will kill any bacteria that may be in it. Deviate from traditional cooking processes at your peril.

It must also be remembered that it is usually a dried product and so lacks the available water needed for bacterial growth.
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Of meat and fridges...

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The Intolerant Chef asks: "How long can raw meat be kept in the fridge before being harmful? I remember my mother washing slightly bluish looking chops in vinegar and water to remove the stickiness and smell before cooking them. They were then fed to my father, never us children or her."

I assume your father was well insured.

Generally, fresh meat can only be kept for a few days at refrigeration temperatures. It is hard to butcher meat without getting bacteria on its cut surface and bacteria love a warm, protein rich surface.

Note: these are bacteria introduced during the butchering process and not endemic to the meat as such. When the meat is 'hung' after slaughter, the surface of the carcass is dry and intact and no bacterial degradation takes place. Once the meat is sliced or minced, bacteria is introduced and all bets are off.

Chilling meat slows bacterial growth but doesn't stop it. Freezing it stops the growth. As does drying.

Bacterial growth results in the breakdown of proteins which in turn produce the unpleasant smells that we associate with 'off' meat. Rubbing the meat with vinegar may reduce the bacterial load and reduce the smell. Traditionally curry was also used to hide off meat.

It would be the thorough cooking afterwards that killed the bacteria and made it safe for your father to eat.

Probably with lots of sauce.
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The Mayo Clinic

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Don says:

"I had the wonderful privilege of touring Mullins Food Products, Makers of mayonnaise.. "(Mayonnaise) doesn't even have to be refrigerated. No harm in refrigerating it, but it's not really necessary." He (the food chemist) explained that the pH in mayonnaise is set at a point that bacteria could not survive in that environment.

(The food chemist) says that when food poisoning is reported, the first thing the officials look for is when the 'victim' last ate ONIONS and where those onions came from (in the potato salad?). Ed says it's not the mayonnaise (as long as it's not homemade Mayo) that spoils in the outdoors. It's probably the onions, and if not the onions, it's the POTATOES.

He explained, onions are a huge magnet for bacteria, especially uncooked onions. You should never plan to keep a portion of a sliced onion. He says it's not even safe if you put it in a zip-lock bag and put it in your refrigerator. "

Ye gods! Where do I start?

The easy bit first: see a previous post on the myth of onions being bacteria magnets. Make sure you read the comments, as the saga went on for a while.

Secondly, there is a popular myth (only in the US for some reason) that mayonnaise is a chief culprit in food poisonings. It isn't. Or at least commercial mayonnaise isn't, as it is made in strictly controlled conditions.

1. The pH of mayonnaise is kept low, at a level that bacteria cannot survive.
2. The water activity of mayonnaise is low, meaning that the moisture present in the mayonnaise is not available to the bacteria (or mould) to use and
3. the product is made in sterile conditions.

The consequences of that last item eludes many people. They think that bacteria just happen. That is as sensible as watching a field, hoping for corn to grow. If you don't plant it, it wont grow.

And "if not the onions, then the potatoes"?

Anything that grows in dirt can have bacteria on it. It will be in an environment where there is E-coli, Salmonella, Clostridium, lots of bugs with long and threatening names. Wherever birds poop and animals roam will have bacteria. You meet up with them every day of your life. And survive.

But if you take some potatoes and cook them there will be no bacteria alive on them.

Put them in a potato salad with mayonnaise and they will still have no bacteria on them.

The biggest problem is when you add bacteria to the salad yourself and then leave the salad sitting unrefrigerated for hours on end. At room temperature bacteria multiply tenfold an hour.

So where do these bacteria come from? Spices, raw unwashed vegetables and, most commonly, poor personal hygiene when preparing the food.

But from the mayonnaise? No.

From onions? No.

From cooked potatoes? No.
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Revisiting Alfalfa Sprouts

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Pythagorian asked: I read your warning about alfalfa sprouts and wonder how and what bleaching methods you recommend. Also I have read a claim that there has never been a case of sprout contamination traced to certified organic sprouts. Do you know if this is true or false?

The common commercial process is shock chlorination of the seeds and chlorination of the water.

The organic claim will be false. The main issue is you have a protein-rich food source that you are keeping wet and warm for several days. Any bacteria present will thrive. This has nothing to do with the organic status of the food, bacteria is naturally present in the environment. In some ways organic produce may have more bacteria. This is not a bad thing, just a consequence of things growing in the open.

Chlorination will kill the bacteria. Other processes might too. My observation is that there is not much margin for error. Warm and wet, bacteria will double in numbers every 20 minutes and most sprouts are eaten uncooked.

The Chinese eat lots of sprouts, without problems, but they stir-fry them and this kills the pathogens.
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Blowers vs Towels

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This is more microbiology than chemistry but it has been a subject that fascinated me. Electric hand dryers in public toilets have long been touted as more hygienic than paper towel.

Not so, it seems.

[Wikipedia] In 2008, a study was conducted by the University of Westminster, London, to compare the levels of hygiene offered by paper towels, warm air hand dryers and the more modern jet-air hand dryers .

The key findings were:

• after washing and drying hands with the warm air dryer, the total number of bacteria was found to increase on average on the finger pads by 194% and on the palms by 254%
• drying with the jet air dryer resulted in an increase on average of the total number of bacteria on the finger pads by 42% and on the palms by 15%
• after washing and drying hands with a paper towel, the total number of bacteria was reduced on average on the finger pads by up to 76% and on the palms by up to 77%.

The scientists also carried out tests to establish whether there was the potential for cross contamination of other washroom users and the washroom environment as a result of each type of drying method. They found that:

• the jet air dryer, which blows air out of the unit at claimed speeds of 400 mph, was capable of blowing micro-organisms from the hands and the unit and potentially contaminating other washroom users and the washroom environment up to 2 metres away
• use of a warm air hand dryer spread micro-organisms up to 0.25 metres from the dryer
• paper towels showed no significant spread of micro-organisms.

And, yes, the work has been replicated.
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Radioactive Calamari

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Every so often we get stories that go along the lines of :

"I went out to the kitchen in the middle of the night to get a glass of water. I didn't turn the light on and I saw the food in the cat bowl was glowing!

Is it radioactive?"

Most spectacular when it is calamari rings.

No, it is not radioactive, it is just active. With bacteria.

Pseudomonas fluorescens. A common spoilage bacteria that secretes a fluorescent pigment. It is generally harmless to humans unless they are already immunocompromised.
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