Rice left in water for several months - what biological reactions or growths would occur?

Question

In an attempt to make a hair care product, uncooked white basmati rice was left in an air-tight container half filled with tap water for several months.

When opening the container, the smell was extremely foul and disturbing, one of the most revolting things I have ever smelt. It was worse than the smell you would usually associate with yeast, alcohol, or mold. This horrid smell immediately spread to the entire property and took many hours of fan extraction to remove. It was worse than the smell of sewage.

I rinsed the container used and cleaned it in the dishwasher several times at 75'c. After several dishwasher cycles, the disgusting smell remains. It makes me wonder what kind of biological or chemical product has been created that even a dishwasher cannot neutralise or sterilise at high temperatures? Is this a safe substance? This is especially concerning as this recipe exists on several hair care forums; is it widespread misinformation caused through malice?

I believe this is a valid scientific question about microbial life so on that basis I would not expect it to be down voted.

The substance looked like water with rice or rice starches dissolved in it; it was murky with a whitish colour. There was no air bubbles which could be visually observed, although the murky texture could have been caused by micro-bubbles. The smell was very strange, unlike anything I have smelled before. The closest description I could give is that of sewage, yet it is more disgusting than the smell of sewage if that is relatable at all.

Answer 1

It is likely a volatile organic compound (VOC) that is released as a by-product of microbial metabolism, although microbes can also produce some inorganic compounds, such as hydrogen sulfide (rotten egg smell). It could be any of a number of compounds, depending on the microbial species and the environmental conditions. The only relevant paper I could find based on a cursory search was by Yanqiang et al. (2013) on volatile compounds released from the anaerobic digestion of food waste in general; based on the results, the odor likely consists of a complex mixture of gases, and may be especially rich in aromatic compounds. Whether it could have any negative health effects is challenging to prove, but you would likely want to avoid exposure.

I presume that your container is made of plastic or at least contains a silicone ring. You can remove odors from metal or glass by washing them, but porous substances like plastics, rubber and the like will absorb volatile compounds, rendering them largely inaccessible to solvents such as water, and will release them slowly over time, which you can perceive via olfaction as you have noticed. If you want to eliminate the odor faster, you will need to accelerate this outgassing process. The way this is usually done is by baking in an oven (optimally in a vacuum, although this is not necessary). The rate of outgassing grows exponentially with the temperature, so you should use the maximum temperature that the material in question can withstand.