The 'Science' of food going bad?
I am very interested in what happens to food as it goes bad. Fresh meat, fruits and vegetables to be more specific. Does any know what is going on there? What gas is given off as the food breaks down? What causes the smell? What is actually happening to the food itself?
If you have any real knowledge about this… please help. I am all ears.
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20 Comments:
Depends on what the food is and what is eating it. For meat, the primary decomposer is bacteria where it is essentially taking up the nutrients present in the tissue for food and using it to grow and divide. Fruits and vegetables have more rigid structure so they are usually broken down first by fungi (i.e. mold) before bacteria can access and use it as food. What is happening to the food itself is that these organisms are breaking down the fats, complex sugars and proteins into less complex units that they can process and use as food. A by product of this process is the gas (and smell) you mentioned - which if I'm remembering correctly is mostly methane and carbon dioxide.
misterhee at 10:22AM on 09/11/09
How about experimenting? You can make your own "Body Farm."
: )
arm1970 at 11:10AM on 09/11/09
The first thing I think of is fermentation: and then I think of beer!
Yeast's goal is to reproduce/multiply. It does this by "budding" to produce a child cell identical to the parent.
Given a sufficent supply of oxygen (exposure to the air), sugar, minerals, enzymes and amino acids, (contents of the product fermenting) it will reproduce itself every 30 minutes and the brewer/fermenter ends up with a bucket full of yeast! Take away the oxygen and you get much less growth and a bucket full of alcohol.
Without oxygen, it can only break one bond and so liberates only a little energy (also little growth to multiply). What's left is thrown out of the cell as a waste product: ethanol.
So, if you want to make booze, keep the oxygen out!
hungrychristel at 11:11AM on 09/11/09
fermentation and decomposition are basically the same thing for the microbes, just different for humans (one, yummy, the other, gross- well, maybe except for things like natto, harmless but gross to many people; to me, yummy!)
microbes constantly compete for their food, so some organisms make toxins to fend off other microbes (which is bad for consumption). you can't really tell this from smell only, so being a microbiologist I'm a bit reluctant to do home fermentation without having access to pure cultures and an autoclave oven.
the odor usually comes from degrading amino acid (from proteins) into amines, which get released with other gas.
fungi are usually more resistant to low pH, low moisture and high salt/ high sugar than bacteria, so things like jam and salt cured foods are usually safe from bacteria but can have mold growth (again, when you get lucky and have beneficial fungi, you can make tasty stuff- think miso!)
hmw0029 at 11:37AM on 09/11/09
Wow... @hungrychristel... you have a way with words. I started reading what you wrote and all I could pick up the first time was:
beer... reproduce/multiply... "budding" to produce a child... will reproduce itself every 30 minutes...
lol
Then I had to regroup... and read again.
I am still thinking about beer now.
happyeats at 11:46AM on 09/11/09
LOL @happyeats: my grandfather used to make his own brew. not really my cup of tea...I like me-self a nice Becks, DAB, or even a Kokanee. Beer is probably one of my favourite things in the world.
Cheers to beer on the brain!
hungrychristel at 12:44PM on 09/11/09
Is it too early in the day to break open a Hop Wallop. You got me thinkin'...
janaatwg at 1:15PM on 09/11/09
Harold McGee in On Food and Cooking says,
"Bacteria and molds break down cells at the meats surface and digest proteins and amino acids into molecules that smell fishy, skunky, and like rotten eggs. Spoiled meat smells more disgusting than other rotten foods exactly because it contains the proteins that generate these stinky compounds"
Can't seem to find the names of the gases they give off, but its a big book and I didn't look too hard. ;) If your'e into food science, I would recommend this book.
sousvide at 2:50PM on 09/11/09
and let's not omit the word "putrefaction."
Also helpful: http://stilltasty.com/ How long things last.
bltzie at 3:12PM on 09/11/09
cool link @bitzie! thx
hungrychristel at 3:48PM on 09/11/09
Let's throw a curve in here and discuss "aging steaks." It's controlled... putrefication...? Something delicious is happening on the inside of the steaks while something nasty is happening on the outside. They need to be scraped before they are cooked but the meat inside is changed, somehow made better - by the very "breaking down" of the meat.
therealchiffonade at 6:47AM on 09/12/09
Sousvide is right - McGee On Food and Cooking is a great read. You'll learn lots of little things you'd never learn anywhere else. And if you're an Alton fan then McGee is one of his sources.
lemonfair at 7:26AM on 09/12/09
Interesting topic. But it makes my head explode when I think about it. So my rule of thumb is if I'm ever in doubt, I toss it. I refer a lot to stilltasty.com. That's a good reference site.
Have a great day.
Ribster at 4:22AM on 09/13/09
Aged steaks are dry-aged in a controlled environment. The mold is external and burned off during cooking. That's why a rare steak differs from a rare burger...with a burger, there is much more exposed surface space (as the meat has been ground).
With things like cheese, there is good and bad mold. Blue cheese or Gorgonzola have good, harmless mold. Some cheeses, like Cheddar, develop a form of 'white mold'. This is less pleasant. And it cannot be scraped off...it has roots invisible to the naked eye that permeate the cheese. So don't be like my grandmother and scrape the green bits off. Cut at least an inch off each side.
On a sidenote, mayonnaise gets a bad rap. There's too much acid in mayo for it to go bad quickly, even when warm. The picnic villain is what's mixed with it...tuna, chicken, eggs, ham. All of these will go bad much sooner than mayo.
NotAmerican at 12:52PM on 09/13/09
Observation from this weekend - watermelon seems to turn into vinegar remarkably quickly. I left a cut open watermelon out (the slice was covered in plastic wrap). After about a week, it was leaking tons of liquid that smalled strongly of vinegar. Suprised since I thought that natual vinegar-ification takes much longer without a starter....maybe I just have the right spores in the air.
tubulus at 3:52PM on 09/14/09
One interesting note I have found over the years is that white mold is rarely worrisome. In many cases it is actually penicillin, and whatever it is, I not only encourage it on my salami when I am curing them, but will happily scoop off little spots o'mold where I see them and eat the rest of the item; tomato paste springs to mind.
Black mold, on the other hand, is no bueno.
As for aging of meat, one man's rotten is another's delicacy. I like to hang my pheasants for several days before gutting them, but I know a few people who will hang for more than a week. The meat stinks by then and will drive everyone out of the kitchen when cooking the bird...but by all accounts, is the finest flavored and tenderest poultry ever eaten. I've not been brave enough to go beyond 5 days.
HunterAnglerGardenerCook at 6:35PM on 09/15/09
I should probably go into another conversation with my thoughts on this but being 40something, does anyone remember being young and having food sit out at parties/cookouts for like ALL DAY and then sit ON THE COUNTER or in the fridge for a week or more while we were still eating the leftovers? It can't be just me. How did we survive?
denise62arizona at 5:30PM on 09/16/09
To keep your beef safe for you and your family here are some tips to remember :
4 C's (Cool It, Clean It, Cook It, Don't Cross It)
1. "Cool It" When shopping, choose your beef items at the end of your shopping trip. When home put your beef in the refrigerator immediately. Total "room temperature" exposure for meat is two hours.
2. "Clean It" When ready to prepare your beef product make sure all cooking surfaces and utensils are clean.
3. "Cook It" When cooking beef, especially ground beef, the magic internal cooked temperature is 160 degrees, for more information go to: www.safeandsavory.com.
4. "Don't Cross It" in other words, keep raw meat and cooked meat separate, never shall the two cross, keep in separate cutting boards, bowls when stir frying and plates for grilling.
For more information about safe cooking go to www.beefitswhatsfordinner.com and www.safeandsavory.com
BeefPA at 6:19PM on 09/16/09
And there is the always useful and interesting shelf-life guide:
http://stilltasty.com/
bltzie at 12:06PM on 09/22/09
http://en.wikipedia.org/wiki/Casu_marzu
Sugar at 12:25AM on 09/23/09