what makes farts really stink?

Answer 1

The previous answers explain why farts SMELL. But why do they STINK? In other words, why do we find the odors offensive?

And by the way - methane itself is colorless and odorless. It's the other stuff that gives farts their odor.

Mammals through time have used their excrements (liquid and solid) to mark their territory (top dog, grizzly bear, mountain lion, bull elk, elephant, etc). So if you are a mountain lion and you enter another lion's territory, you will smell the local animal's scents and know who was the boss. You also learned to move away (or expect to possibly get into a fight with the local "boss" over who is in charge around here).

So mammals over time learned a genetic distaste for other mammal's fecal smells. Bring this to today - other people's farts are more distasteful and repulsive to people than their own (admit it - and ask your friends!).

This "distaste" is perceived by us as "stink."

Answer 2

Short chain fatty acids and sulphur dioxide give flatus gasses their perculiarly disgusting odour.

Wiki says:
The gas released during a flatus event frequently has a foul odor which mainly results from low molecular weight fatty acids such as butyric acid (rancid butter smell) and reduced sulfur compounds such as hydrogen sulfide (rotten egg smell) and carbonyl sulfide that are the result of protein breakdown. The incidence of odoriferous compounds in flatus increases from herbivores, such as cattle, through omnivores to carnivorous species, such as cats or dogs. Flatulence odor can also be caused by the presence of large numbers of bacteria and/or the presence of feces in the rectum.

Answer 3

From the plates of teen-agers come strange foods, that when mixed in the stomach, drained of nutrients, and allowed to sit in the intestinal system for a day or two generates methane and other organic gases that give "farts" their unagreeable odor.

Answer 4

pinto beans, beer, cabbage and a glass of milk