As an alternative to tofu and a great source of protein, tempeh is a soy-based product that achieves its dense and nutty flavor with fermentation. Because you use a bacterial starter to make tempeh, it can be challenging to know when tempeh is ready to eat and when it reaches the point of spoilage.
If you notice black spots on your tempeh, they are a sign of mature fermentation and are okay to eat. Healthy mold is necessary to form tempeh, but it can be difficult to tell is the different colored growths are good or bad. Black spots are the growth of spores that indicate the full maturity of the Rhizopus mold used to make tempeh.
Understanding the indicators of edible vs. spoiled tempeh will keep you safe and prevent unnecessary food waste. With other foods, black spots often indicate mold that shouldn’t be present. Because tempeh is made of mold, you do not have to worry about dark spores. This article discusses the key signs of when your tempeh is expired and should not be eaten.
What Are Tempeh Black Spots?
After soybeans have been soaked, they are placed into an environment with Rhizopus, a fungus used to create a mold that binds the soybeans together (Source: Science Direct). The black spots you see on tempeh are the creation of spores, or new mold growth specific to Rhizopus fungi. These spores typically appear white, gray, or black.
Black spots are one of the final steps in the fermentation process, which is necessary for tempeh creation. The following steps outline the process of fermentation used to make tempeh:
- You must first cook the soybeans to create the desired texture and allow for consumption.
- Remove the hull from the soybean as the hulls are a by-product of the seeds and are not meant to be consumed by humans.
- After cooking and cooling the soybeans, you should place them in a tray with Rhizopus to form the binding mold, mycelium. This binding mold is responsible for holding the tempeh together (Source: Applied Microbiology).
- Incubate the mixture at a steady temperature to allow for this fermentation process to bind.
- Black spores will appear to reproduce the Rhizopus, which signals the completion of the fermentation process.
As the tempeh sits refrigerated (it should always be refrigerated), it continues to ferment, allowing the black spores to appear (Source: How Stuff Works). Once black spots have covered the tempeh, it is at full maturity and has its strongest flavor.
Once the spores on the tempeh have turned black, they are fully matured and have reached their peak flavor. If you notice any growth from these spots or additional mold growth, this may suggest that unhealthy bacteria have developed, and you should not eat the tempeh. Any black spots that form within the expiration time frame should not cause any worry.
If you have ever looked at a mushroom’s underside, the spores found on it and the tempeh are very similar and signal reproduction. This is simply a visual indicator of growth for the Rhizopus fungi.
Is It Okay to Eat Tempeh with Black Spots?
Because these black spots are harmless, you can and likely will eat tempeh with some gray or black spots on it. You can think of these as similar to the blue marbling that appears on blue cheese, which appears to be strange but is completely harmless. Ensuring that your tempeh remains fresh and edible is still important despite dark spots that may appear.
Storage is one of the most important factors for keeping your tempeh from spoiling. Especially in larger packages, it can be challenging to eat all of your tempeh before it starts to go bad. If you store your tempeh in the refrigerator, you will want to consume it before ten days have passed. When frozen, tempeh can last up to 10 months (Source: Still Tasty).
If purchasing store-bought tempeh, you can typically use the stated expiration date as a good baseline for quality. However, this should not be the sole decision-making tool, and you should examine the tempeh before consumption.
It is important to remember that your tempeh should be cooked before eating, unlike tofu. It is not encouraged to eat raw tempeh because there may be additional growth beyond the Rhizopus fungi. Raw tempeh is only safe to consume when it is freshest, which can be difficult to determine when it is bought from a store. Raw tempeh is not cooked after the fermentation process, as the soybeans are already technically cooked (Source: Superfood Evolution).
Has Tempeh with Black Spots Gone Bad?
If your tempeh has black spots (or grayish and white), it has not gone bad. You will often notice this when you leave the tempeh in its packaging because it continues to ferment and incubate at consistent temperatures (Source: Cultures For Health). The black spots may be a distraction from actual spoilage that is more difficult to identify on your tempeh.
While black spores will not be a concern for spoilage, there are some key indicators you should be aware of after about 7-10 days that may suggest the tempeh has gone bad:
- Smell: This is the number one indicator that your tempeh has spoiled. Before consumption, especially if the tempeh has been sitting for longer, you should give it a quick sniff. If the tempeh has a rotten, alcohol, or ammonia smell, you should not eat it (Source: Peta).
- Mushy or slimy texture: The physical texture is also important to examine. Tempeh should be dry and firm in its edible condition. If you notice any slime in the packaging (not water) or very soft or mushy consistency, do not consume it.
- Dark bean coloring: Your cooked soybeans should maintain their white to light coloring. Dark beans are another sign of spoilage. These will need to be a noticeably dark color and used as a secondary indicator in examining the tempeh. You do not need to worry about this if you are using a black bean for the recipe.
- Additional mold deposits: While black and gray spots are perfectly normal, if you notice any other colored spots or additional growths on the tempeh, you should not eat it (Source: Fermenters Kitchen). These could be signs of unhealthy bacterial growth that appear as the tempeh ages. You should not consume the tempeh if these growths appear to be hairy or fuzzy.
If you are consuming tempeh within the allocated window of freshness and do not see any clear red flags listed above, you should not be concerned when eating tempeh with black spots. It is always recommended to check your tempeh before consumption.
Enjoying Tempeh with Black Spots
In traditional western culture, the presence of mold and bacteria is a bad sign when it shows up on our food. Most people tend to stay away from foods that have growths or strange coloring to keep themselves healthy. This makes it easy to fear eating tempeh, even though it is perfectly safe and healthy with gray and black spots.
In Indonesian culture, where tempeh was created, many recipes actually call for tempeh that has been completely covered in the black spots. This suggests the peak level of maturity and the best overall flavor. The flavor profiles are often the most intense at this stage to enhance their taste within a dish.
Since you now know that tempeh is safe (even with black spots), you can enjoy this protein source rich in vitamins and minerals that are extremely beneficial for digestive health (Source: Healthline).