Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

O.K. here’s the scenario.  You’ve just dragged yourself home after a long hard day’s work and you’re starving.  You certainly don’t feel like cooking and you know that there are plenty of wonderful leftovers lurking in the fridge.  Now, let’s see, here’s the bultang from Shareen’s Sweet 16, and there, farther back is the plate from Tun Jose’s birthday party.  Oh, yeah, that was some righteous kelaguen!  And over there is the container of pork adobo from last Saturday.  Ah me, decisions, decisions, decisions.  I think we’ll start with the kelaguen.  Hmmm, looks OK . . . GACK!! That STINKS!!!  No kelaguen tonight, that’s for sure!

Familiar, eh?  So, here’s what distinguishes most of us from the scientist.  Did you ever wonder WHY it stinks?

The short answer is pretty simple although its discovery is fairly recent.  Food goes bad because of decomposing bacteria.  We are typically very disgusted by these particular microbes.  Most of us don’t want to think about the ultimate fate of all living things, which is to be broken down into their component parts by these microscopic creatures, but the decomposing bacteria are extremely important to all of us.  One of the primary reasons is that if they didn’t exist, we soon be up to our you-know-what’s in corpses.  My word, wouldn’t THAT be unpleasant!  And eventually we’d all starve (including all the plants) because there wouldn’t be anymore raw components to build life from.

But that still doesn’t answer the original question.  Why does that kelaguen stink so bad?  Why do decomposing bacteria produce putrescine and cadaverine and all those lovely sulfur and methane compounds that make us want to run for the hills when we smell them?

Smell is the oldest and most primitive sense.  You see and hear with the more advanced parts of your brain, but the chemical pathways that allow you to smell a rose (or a dirty diaper) are embedded in the brain’s most primitive areas.  We have excellent memories for odors and smelling certain things can evoke an almost physical memory of your surroundings when you first smelled that particular scent.

Smell is important.  The mammalian genome has at least a thousand genes that make different odor receptors.  No more than 40% of these genes are functional in humans, however, which probably explains why dogs are better at detecting orders than we are.  But even for humans, smell is an important part of the way our environment communicates with us.  So . . . . why does that kelaguen smell so bad?

Scientists have been doing some research in that very subject and apparently the answer is that the kelaguen smells bad, so we won’t eat it.  Well, duh . . . . why would I want to eat something that’s rotten?

Interestingly enough, (depending on how long it’s been in the fridge, of course) most of the kelaguen probably isn’t rotten.  Bacteria don’t infest their food all at once, they start on the outside and work in.  And many of the chemicals that warn you away from the decomposition process are not inevitable byproducts.  In other words, the bacteria manufacture these particular chemicals specifically to keep you from eating their food.

Scientists working with stone crabs did some interesting experiments with rotting fish.  They placed dead fish in two pools for two days.  One group had no controls, the other pool was full of an antibiotic that prevented the growth of bacteria.  Natural decomposition (the ‘nice’ name for rotting) occurs without bacteria, but at a much slower pace.  The stone crabs readily ate both freshly thawed fish and fish from the antibiotic pool, but refused to eat the rotten fish not protected from microbial attack.

Then they took chemical compounds from the bacteria-laden fish and added them to fresh fish.  Sure enough, the crabs refused to eat the fresh fish when it smelled bad.  I suspect that if someone smeared putrescine (a non-toxic chemical, by the way, you can eat it all day long) on a nice juicy steak, I wouldn’t eat it either.

There are bacteria everywhere.  Without bacteria, there would be no cottage cheese, no yogurt and (horrors!) no beer.  You’d die because the bacteria that live in your gut digest most of your food for you.  But it comes as a bit of a shock that they are trying to steal my food from me!

So the next time you open your kitchen science experiment and smell the kelaguen, remember that someone else may have gotten there first (and I don’t mean your teen-age son!)

Cruise on over to the Deep Website at www.thedeepradioshow.com to learn more about bad smells and many other topics.  Enjoy!