What causes odd off-flavor/smell in tofu?

Going bad.

It's not necessarily unsafe to eat yet, but tofu can pick up a slightly spoiled flavor even before it goes bad.

Especially since tofu has so little flavor of its own, it's easy to taste if it goes slightly off.

You can mitigate this by storing it in clear water and changing the water frequently.

It probably was some reaction of the calcium chloride which produced a smellable compound. Tofu is coagulated with calcium chloride (sometimes also magnesium chloride), which has its own taste, but does not generally have a detectable smell (see for example http://chemse.oxfordjournals.org/content/21/4/417.full.pdf).

In principle, a "chemicaley" smell could be anything, but with your association with Clorox, a chloride compound is a very likely explanation. I cannot say which exactly, and a cursory search didn't reveal a specific candidate, although I guess it is a problem known to food technologists.

I have encountered the EXACT same thing with the exact same brand of tofu you used - Trader Joe's Organic Sprouted Extra Firm (and sometimes with other brands too).

The tofu wasn't old or expired; the expiry date on the packages were still fine, but there was this odd smell and taste. It was subtle, but there. Other times the smell was so intense it was gag-inducing and I instantly had to throw the whole thing away.

Like you said, it has a "chemically", Clorox-like smell, maybe a bit fishy too. In fact it smells like something that is too gross for me to mention on this forum. To my knowledge, no one got sick either.

Several times I still attempted to cook the milder smelling tofu, since the expiry date was still fine, but had the same reaction as your daughter - I spat it out. My husband however, didn't mind, but was able to detect a subtle difference.

All of this suggests to me that it's the same issue you identified.

My thoughts on this:

• I have been regularly eating supermarket tofu in NYC for at least a year and possibly two before I ever noticed something like this. When it did start happening it was all within the same period of time. My assumption was that there was a sudden change in manufacturing process, and not necessarily a typical issue. That being said, I could have just been lucky for those first two years and maybe this is actually a common problem.
• What changed: At first I suspected contamination, but the absence of food poisoning and the 'chemically' smell made me think it might have to do with the coagulants. Perhaps they changed their ratio of coagulant used in their formula, or started using different kinds of coagulant (calcium sulfate, calcium chloride, magnesium sulfate, or magnesium chloride).
• This may also explain a secondary detail I noticed which is the texture. I used to like the super firm tofu, but have come to dislike it, and I suspect the culprit it also a change in the coagulation process. If I recall, the tofu which had that weird smell also had a slightly different texture - still super firm but instead of a smoother texture (from a longer pressing time) the "grain" of the tofu seemed more "crumbly", like the curds might have over-coagulated.

Sorry for this very lengthy answer. I am also just very curious as to what could be the issue and have yet to find a resource on the web explaining this. I guess I will have to do further research!

Sounds like a pack that was left unrefrigerated for more than several hours. This is most prone to happen during poor shipping practices or packs being removed from refrigeration by a customer then the customer decided they didn't want it anymore and left it on some random shelf or at the register. None the wiser an associate would put these items in a cart to be sorted later etc.

Faint Sour Smell can be washed and still consumed.

mild to strong rotten breath or rotting teeth smell needs to be returned and explained to the grocer or thrown out.