Tofu

Opened tofu keeps 3–5 days refrigerated and about 5 months frozen.

Once the package is open, store the tofu submerged in fresh cold water in a covered container, and change the water daily. This is the whole technique — the water excludes air and washes away the bacteria and dissolved proteins that accumulate at the surface. Tofu stored dry in a container turns slimy in a couple of days.

Unopened refrigerated tofu is good until its printed date. Shelf-stable aseptic packs keep in the pantry until dated, and go in the fridge once opened like any other tofu.

Freezing changes tofu fundamentally, and many people freeze it on purpose. The water inside forms ice crystals that rupture the structure, leaving a spongier, chewier, more absorbent block that holds marinade far better. It also turns beige or yellowish, which is normal and not a spoilage sign.

Tofu is not a dairy product, but it fails in ways that make it worth understanding alongside them — and it is one of the more perishable things in a refrigerator.

The composition is the reason. Tofu is high in protein, high in moisture, low in acid, low in salt, and low in sugar, with a pH close to neutral. That is essentially a laboratory growth medium. It has none of the barriers that protect cheese — no significant acidity, no salt, no reduced water activity — and none of the live culture that protects yogurt by competing with newcomers.

So the 3–5 day window is short for a good reason, and the daily water change is not fussiness: it physically removes accumulating bacteria and the leached proteins they feed on.

Spoiled tofu is easy to identify, because it does not hide. A slimy or slippery film on the surface is the first sign. The color shifts from bright white to tan or yellow. The smell turns sour and sharp — fresh tofu smells of almost nothing, faintly beany at most. Any of these means discard.

The cloudy water in a freshly opened package is normal, as is a faint bean aroma. Freezing's yellowing and spongy texture are also normal and permanent.