Tempeh, as a living protein, should be respected and treated like any high quality fresh produce.
It should be stored either in the refrigerator, where it will last 7- 10 days or kept in the freezer until ready to use, where it will last for 4-6 weeks before the freezing process starts to break it down.
Tempeh has a fermented element, and it will continue to ferment in the fridge. Time should be taken to understand this process and at what point of fermentation is most delicious to you. Think of it as ripening fruit; with each day, the flavor evolves.
To know if tempeh has “gone bad,” there are a few rules of thumb to follow. First if it feels slimy to touch, secondly if it has a strong ammonia odor or generally smells awful and lastly, use common sense. When in doubt throw it out.
Some black spots and black patches may be present on the tempeh. This is actually the fruiting stage of the tempeh, is completely natural and does not denote the product has gone bad or is contaminated.