Re: Why does hot sauce get brownish spots in it? is it bad?

"Follow-up question":
Hot sauce has such a high acidity to it from the vinager, that it shouldn't go bad. SO why is there brownish patches floating in my sauce?

Answer:
A problem with this question is that it does not specifically define "hot sauce." It seems clear that this has something to do with hot chilis, but there are other ways of making sauces hot. Further, various on-line references give hot sauce formulations without vinegar. The follow-up question specifies vinegar, but not how much. Commercial products are required to list ingredients in order of the quantities present. The two commercial hot sauces in my house have chili peppers first and vinegar second in one instance, and vinegar first and chili peppers second in the other, plus various minor ingredients.

The active preservative substance in vinegar is acetic acid. This is usually made by bacteria from alcohol, sometimes accidentally. Our word vinegar comes from French vin aigre, meaning "sour wine." At sufficient levels, acetic acid is very effective in preventing growth of bacteria. However, molds can grow in highly acid foods, and they can use acetic acid as an energy source, which eventually makes the food less acid. Molds generally require oxygen (air) to grow.

When you speak of "my sauce," I can't tell whether this is a commercial product or something that you made yourself. I surmise that it has vinegar in it, but I can't tell how much. The phrase "brownish patches floating" suggests that the hot sauce is in a container other than the narrow bottles with narrow delivery holes that are used commercially.

There are a number of things that happen to foods during processing or preparation that are called "browning reactions." I don't think that any of these is your problem. Assuming that the hot sauce is something you made and stored in a broad container, any heating that might have been done probably killed most of the bacteria and nearly all of the molds. However if the sauce was exposed to air during cooling, it may have received a few airborne mold spores that, because of the wide container, had a lot of exposure to air. These could have produced colonies of mold rapidly at room temperature or more slowly in the refrigerator. If my guesses are correct, I would suggest discarding this hot sauce, even though most food-spoilage molds are not threats to consumer health.

If you haven't had a laboratory course in microbiology, it will be difficult to verify my guess. Assuming that the brown spots are at the surface of the hot sauce, you could look at the spots through a high-powered magnifying glass under a strong light. If the surface looks fuzzy, it is mold.

Experimental confirmation is not out of the question, but accuracy is not guaranteed if this is done at home. If you feel like trying this, you will need: a not-too-old slice of bread that has no preservatives (e.g., BHA or BHT) and has not been handled with bare hands, two sterile cotton swabs (e.g., Q-tips, or whatever), and two small glasses (e.g., shot glasses) of tap water that has been boiled to drive off chlorine and then cooled. Dip one swab in the water and rub it on the surface of the bread near one edge. Dip the other swab lightly into one of the brown spots, mix it in the water in the other glass, and rub it on the surface of the bread near the opposite edge. Without touching the slice of bread with bare hands, slide it into a sandwich bag with a zipper lock and seal the bag. Store this in a dark place at room temperature and look at it at least once a day. What you may see is mold growing on the bread where you applied the sample from the brown spot in the hot sauce and not where you applied the boiled tap water. Be sure to do the tap water "control" before you do the sample from the brown spot. If you want to be extra careful, you may want to use separate slices of bread in separate sandwich bags. I can't guarantee what will come of this because a trained microbiologist handles things differently from other people; but if you want to expend one or two slices of bread in the interest of science, go for it!

Dean O. Cliver
Possible reading: Hajmeer, M. N., and Cliver, D. O. Ch. 22. Microbiology of food preservation and sanitation, pp. 331–352. In Cliver, D. O., and Riemann, H. P., eds. 2002. Foodborne Diseases, 2d ed., Academic Press, London. xvii+407 pp.