How to Tell If Tempeh Is Bad: A Practical Guide

Tempeh is one of the best sources of plant-based protein you can find. It’s a top meat substitute for vegans and vegetarians worldwide. But despite its rise in popularity, its fermented nature also leads to many questions—like how to tell if your tempeh is bad.

Rotten tempeh usually has a strong smell of ammonia or alcohol. The texture of rotten tempeh often becomes mushy or crumbly, as well. Gray and black mold spots are expected and safe on tempeh, but a greenish fuzzy mold is not safe and should be discarded.

If you’re looking for a practical guide for tempeh storage and whether yours has gone bad, you’re in the right place! Read on for more tips on spotting rotten tempeh, as well as how to store it correctly. Let’s dive in!

Normal Tempeh vs Bad Tempeh

The fact that tempeh is a fermented product with an uneven color profile makes it difficult for newbies to tell if it’s normal or rotten. Many people think their tempeh is bad when it’s actually just fine.

The best way to understand the difference between normal tempeh and rotten tempeh is by putting them in direct comparison in terms of shape, smell, consistency, and more.

Before I cover the general principles to look for, though… take a look at this:

I conducted an “experiment” to get the above picture. I purchased a block of Lightlife tempeh from the store, and I kept it in my bedroom for 6 months without opening it.

Luckily, it didn’t start smelling through the package or anything. Anyway, after 6 months, I opened it up, and I compared it to a new, fresh block of tempeh (same brand).

The visual difference is not huge—the 6 month-old tempeh looks a bit more dried out and slightly darker. But the smell was actually the biggest difference. The old block smelled a bit like alcohol. And as you’ll read below, this is for good reason.

So without further ado, let’s cover the common differences between fresh tempeh and rotten tempeh.

Outer Shape

To understand the shape and texture of normal tempeh, you should know what tempeh is made of. First, tempeh is a protein product that’s originally popular on the island of Java in Indonesia.

What makes it special is that it has a cake texture that makes it excellent for fake bacon. Due to its firm nature, most tempeh is stored in the form of blocks.

As a rule of thumb, a fresh block of normal tempeh should be firmly packed. The tempeh cake block is usually covered from the outside with a white mold known as “mycelium” or “Rhizopus oligosporus”.

However, you shouldn’t be freaked out from this “mold”! This mold is the secret behind tempeh’s fermentation process. In fact, this mold is actually considered healthy, with multiple benefits to your body. Also, it’s one of the components that gives tempeh its taste!

This layer is, in fact, a form of fungi filaments that are supposed to ferment the block and cover it completely. That’s why you should find it throughout the whole block, holding it together tightly.

In a rotten state, the outer shape of tempeh can change in a variety of ways. For example, if you find the outer layer having different forms of mold or change in the color other than greyish or whitish mycelium, then it’s rotten tempeh you should get rid of.

Texture

As you already know, the mycelium layer holds the tightly packed tempeh together from the outside. So a good block of tempeh shouldn’t be too mushy when you press it with your finger.

Moreover, the mycelium layer shouldn’t only cover the block from the outside, but it should also cover each bean separately. Think of it as the cement that holds the entire block together. So, normal tempeh shouldn’t have any openings or gaps between the filaments and the beans.

On the other hand, rotten tempeh will start to change in texture. When you lift a rotten block of tempeh, it might start crumbling noticeably. In other cases, it might get a bit slimy or mushy, which you’ll find as you pick it up or press it.

Consistency While Cutting

As you cut normal tempeh, the slices will come out neatly in a consistent shape. It’ll be firm but easy to cut through.

However, cutting rotten tempeh will be troublesome. The slices will start crumbling and it won’t easily cut with a kitchen knife.

How Should My Tempeh Smell?

The smell is one of the easiest ways to distinguish between normal tempeh and one that has gone bad.

Ideally, a block of tempeh should have an earthy or a nutty smell coming mainly from the mycelium layer. The smell should be close to what edible mushrooms smell like.

On the flip side, a rotten smell is the first thing that gives rotten tempeh away. The rotten smell usually has a strong odor of pure alcohol or strong ammonia. Once you smell that, the remainder of the block should be discarded.

However, a very faint hint of ammonia is considered normal, as the tempeh will produce it as it grows. Yet, you should know that this block is on its way to going bad.

Are Black Spots Normal in Tempeh?

This appearance is OK and nothing to worry about.

Once you pull the tempeh out of its wrapping, you may find that it has some black spots on it. These spots may be small specks, or big and covering much of the tempeh’s surface.

You may notice these spots forming around the air holes specifically, especially if the tempeh is homemade.

In some cases, you might even find the white mycelium layer turning greyish to dark grey. These black spots are in fact a part of the maturation and ripening of the mycelium as it reaches maturity.

You should not be worried about these gray and black spots. In fact, on the island of Java, some recipes require overripe tempeh blocks that are very dark in color.

The tempeh block should be edible as long as it has no other signs that it has gone bad—such as a strong ammonia smell or crumbling texture.

What Happens If You Eat Bad Tempeh?

Tempeh goes bad when the mycelium fungus loses the battle against more dangerous strains of fungus. While tempeh is a highly nutritious food, rotten tempeh can cause a wide variety of problems.

How your body specifically handles bad tempeh will depend on your body’s immunity and tolerance to the fungus.

In most cases, bad tempeh can cause stomach upsets, nausea, and vomiting. Though rare, bad molds can produce dangerous substances known as mycotoxins and aflatoxins, which can increase cancer risk, as well.

Can Tempeh Give You Food Poisoning?

Tempeh is supposed to come wrapped in a protective cover to keep it from flies and bacteria. Although mycelium has some antimicrobial properties, which is one of its benefits, exposed tempeh can potentially cause salmonella infection.

This condition can cause a wide variety of symptoms which shows 12 to 36 hours from digestion, including:

  • Abdominal cramps
  • Diarrhea
  • High fever
  • Vomiting

What If My Tempeh Is Fuzzy?

As you know, tempeh is covered by a layer of mold known as mycelium. This layer is originally white in color and can darken with time as the mold matures and become ready to make spores.

However, fuzzy food is caused when billions of spores are waiting to be blown to new environments.

A grayish green fuzzy mold is a sign that the tempeh block is infested with another form of mold. As a result, you should discard the block immediately, as it can cause serious symptoms.

According to the Food and Drug Administration (FDA), consuming this kind of mold carries serious risks, ranging from severe allergic reactions all the way to fatalities.

How Long Is Tempeh Good for Unopened?

Since molds can grow in environments low in oxygen, even unopened tempeh can go bad.

The exact answer still depends on storage conditions. However, if the tempeh is kept unopened at room temperature, it can last anywhere from 1 day all the way to 3 days before it starts over-ripening. This also depends on its packaging and preservation.

If you’re keeping your tempeh in the refrigerator, check the expiration date on the package for when you should ideally eat it by.

How Long Can You Keep Tempeh in the Fridge?

Refrigeration below 4 °C (40 °F) can prolong a tempeh block’s shelf life. However, it can’t make your tempeh last forever.

If you keep your tempeh block in the fridge sealed in its incubator wrapping, it can last anywhere between 3 days and up to a week. In my experience, tempeh usually lasts anywhere between 5 to 7 days.

The storage life of tempeh can also extend to up to 3 or 4 weeks if the block is steamed or blanched before refrigeration. This inactivates the enzymes that speed up the rotting process.

Store-bought tempeh packages will often come with an expiration date that is a month or two away, so you can store those for a bit longer.

You can also freeze a tempeh block, which can help it to last for 12 months with minimal change in flavor and texture.

Summary

You now have an idea of everything you need to know about storing tempeh. Using this practical guide, you should be able to tell if your tempeh has gone bad or is still safe for eating.

Black spots on tempeh aren’t anything that you should worry about. However, the change in smell to a strong ammonia odor, or a crumbling or mushy texture, are red flags that you should discard the tempeh block.

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