Fresh tofu has a very mild aroma and a moist surface, but it should not smell sharply sour or develop a slimy, slippery coating. Tofu is high in water and protein, so once opened it requires refrigeration and clean handling. Oregon State University Extension specifically notes that spoiled tofu can have a strong sour smell and feel slimy. When those changes appear, discarding the product is the practical choice. Rinsing the block, covering it with a strongly flavored marinade, or cooking it does not reverse obvious deterioration.
What normal tofu looks and smells like
Fresh tofu is usually white to ivory with little aroma beyond a mild cooked-soy note. Firm styles feel moist but hold a clean solid surface; silken tofu is more delicate and breaks readily, yet it should not be coated in slime. Packing water may be clear or slightly cloudy depending on the product. A pronounced new sour smell combined with slippery texture is a different situation.
Color and texture can change for legitimate reasons. Freezing tofu often makes it slightly darker, firmer, chewier, and more sponge-like after thawing. That known physical change is not spoilage when the tofu was fresh before freezing and was thawed safely. Storage history helps separate an expected texture shift from deterioration that develops during several days in the refrigerator.
Sour odor and slime are strong spoilage signs
A sharp acidic, fermented, or otherwise unpleasant odor that was absent when the package was opened is meaningful. If the surface also becomes slick, sticky, or stringy, the tofu no longer resembles a fresh product. There is no need to taste it for confirmation. Flavoring can hide an odor but cannot correct the microbial or chemical changes that produced it.
Discard tofu with mold, abnormal pink, green, or dark patches, unexpected gas, or a swollen package as well. If the storage liquid becomes thick, stringy, or foul-smelling, simply draining it and keeping the block is not a sound salvage method. In a moist food, visible deterioration may not be confined to the exact area that looks worst.
How to store tofu after opening
Oregon State University Extension recommends refrigerating tofu after opening and, for tofu kept in water, covering it with fresh water and changing that water daily. Use a clean container and clean utensils. Changing the water can help maintain quality, but it does not restart the product’s age every day. Open tofu is still perishable and should be used promptly.
Do not leave an open block at room temperature for a prolonged cooking session. Cut what you need and return the rest to refrigeration. Follow package-specific instructions because shelf-stable silken tofu and refrigerated water-packed tofu may have different unopened storage requirements, even though both need careful handling once opened.
How to decide when a block is questionable
If tofu is within a reasonable storage period, has remained cold, smells neutral, and feels moist but not slimy, it may still be in good condition. Slightly firmer texture after freezing or mildly cloudy packing water should not automatically be confused with spoilage. Evaluate the whole product and remember how it has been handled since opening.
Discard tofu when strong sour odor, slime, mold, unusual color, gas, swelling, or questionable refrigeration is present. Washing the surface does not remove the process that caused those changes. To reduce waste, buy package sizes that match your use, date opened containers, and freeze fresh portions when you know they will not be eaten soon rather than leaving an uncertain block in the refrigerator.
A shelf-stable aseptic package can have a very different unopened life from refrigerated water-packed tofu. Once opened, however, the protective sealed environment is gone and the tofu should be handled as a refrigerated perishable food. Do not use the unopened shelf life as a reason to keep an opened block for an unusually long time.
Sources
- Oregon State University Extension — Tofu — Gives opened-tofu storage guidance and identifies strong sour odor and sliminess as spoilage signs.
- FDA — Are You Storing Food Safely? — General refrigeration and suspicious-food disposal guidance.
- FoodSafety.gov — Food Safety During Power Outage — Reference for perishable foods after loss of temperature control.