How To Tell If Blueberries Are Bad To Eat? Here Are The 4 Signs!

Look for signs of mold, especially on bruised or damaged fruits. Moldy blueberries can have a bitter taste and are unsafe to eat due to potential toxic spores.

Blueberries, cherished for their sweetness and convenience, face preservation challenges due to their soft, porous nature, making them prone to spoilage and mold. Recognizing bad blueberries goes beyond spotting mold; consuming parts seemingly unaffected can still pose health risks due to toxic spores.

Our concise guide offers essential tips on identifying spoiled blueberries and maintaining their freshness, ensuring you enjoy these delightful berries safely and avoid food poisoning.

Key Takeaways

  • Mold growth, particularly on bruised areas, is a primary indicator of bad blueberries.
  • Soft, mushy texture and discoloration signal overripeness and potential spoilage.
  • An off-putting or sour odor is a sign of decay and should be avoided.
  • Visible insect damage can lead to quicker spoilage and potential contamination.
  • Proper storage, including refrigeration and avoiding washing before storage, can extend the shelf life of blueberries.

What Happens If You Eat Bad Blueberries?

Evaluating the quality of blueberries is vital to find out if those berries are safe to eat. One of the simple ways to check blueberry freshness is to conduct a blueberry quality assessment through its physical appearance.

In general, blueberries that are no longer safe to eat will show some changes, such as becoming mushy.

This occurs due to overripe, which causes the texture of the fruit to soften. In addition, the acidity level becomes high. Thus, the taste of those blueberries will be sour and rancid.

Despite experiencing a decrease in quality, these berries are safe to eat.

how to tell if blueberries are bad
What Happens If You Eat Bad Blueberries?

On the other hand, you have to leave and ditch the blueberries if you spot mold. Mold growth is one of the massive signs of spoiled blueberries. The fungus generally grows on bruises on the berries, which leak the juices.

Blueberry juices contain sugar and water, the medium for mold growth. Not only growing the mold, but the bruises will also trigger bacterial contamination, rotting the blueberries fast, including the fresh ones.

These bad blueberries taste like rotten fruits with a bitter and rancid aftertaste.

In case you happen to eat them, you should immediately spit them out as the mold usually produces poisonous spores which will make you sick.

Some symptoms of food poisoning caused by spores are generally nausea, diarrhea, fever, and shortness of breath. If you experience such signs, you must ask for medical help.

Look for Visual Cues of Blueberries

As we previously mentioned, the first step in blueberries spoilage detection is to look at their physical appearance. There are some blueberry spoilage indicators you can notice.

Some of them that are visible are mold growth, discoloration, changes in texture, off odor and taste, and damage due to pests.

how to tell if blueberries are bad
Look for Visual Cues of Blueberries

To know more about the details of blueberry decay symptoms and how to tell if blueberries are bad, let’s discuss more below!

1. Molds or Unusual Growth

The easiest way to tell if blueberries are bad is by looking for signs of mold. Molds will grow when the fruits are not in good shapes, such as bruises.

Scars and bruises will leave open areas on the skin that will eventually leak the juice.

With high humidity and warm temperatures, mold growth will be faster. Blueberries also contain high water and sugar content, making fresh blueberries turn into bad ones quickly.

These fungal organisms will break down the sugar content in the berries, leaving you with the bitter taste of the fruits. As the process of breaking down this sugar goes on, it also changes texture. Your firm, slightly soft blueberries will be mushy.

In addition, blueberry skins are porous. It will let the fruits absorb more moisture from the environment, giving them a short shelf life as they are prone to bacterial and fungal infections.

Pests, like insects, also favor this humid condition.

Furthermore, 11 fungi commonly infect blueberries where you can use them as a benchmark for early blueberries spoilage detection are:

  • Anthracnose Rot (Colletotrichum Acutatum) – Orange, wet spore masses. Commonly found in blueberries stored at room temperature.
  • Alternaria Rot (Alternaria Spp.) – Greenish-gray micellium and olive green spores. Generally spotted on the stem bruise. 
  • Gray Mold (Botrytis Cinerea) – Fluffy gray micellium with brown stalks. Occurs in post-harvest treatment.
  • Phomopsis Rot (Phomopsis Vaccinii) – Creamy-brownish, piimple-like shapes all over the fruit. 
  • Pestalotia Rot (Pestalotia Vaccinii) – Black spores with creamy-grayish micellium.
  • Hainesia Rot (Hainesia Lythri) – Button-shape, pink to red spore masses which will turn brown to black as they dry.
  • Yeast Rot (Aureobasidium Pullulans) – White, pinkish slime or black and white bumps. Fruits are slimy when yeast rot infests them.
  • Aspergillus Rot (Aspergillus Spp.) – Powdery, brown-black spore masses with white stems. 
  • Epicoccum Rot (Epicoccum Nigrum) – Orange-yellow micellium commonly spotted on stem scars.
  • Rhizopus Rot (Rhizopus Stolonifer) – Brown to dark brown stalks with round, dark gray spores on the tip.
  • White Mold (Trichoderma Spp.) – Fluffy, white cotton balls mycellium on the blueberry skins.

2. Discoloration or Softness

Texture and color are a few indicators for the blueberry freshness test. Fresh blueberries have a delicate texture, deep purple with touches of blue color and a white waxy coat.

Knowing this fact, it’s no wonder that one way to check blueberry freshness is to observe the texture by touching the berries.

The change in texture from delicate to softer and mushy indicates over ripping blueberries. This may be due to the degradation of cell walls and an increase in water-soluble pectin, which causes softening of the blueberries.

how to tell if blueberries are bad
Texture and Color are a Few Indicators for The Blueberry Freshness Test

Apart from the two factors above, softening berries can be one of the pinpoints of bad blueberry identification. It especially applies if you detect mold growth along with the texture change. These molds usually grow on areas of stem scars or bruises on the skin’s surface of berries.

Moreover, they will consume sugar, their favorite growth medium, leading to a change in texture. Besides, your blueberries will also experience discoloration due to the chemical reaction.

The deep purple with blue hues of common blueberries will further turn purplish, with a brown hint indicating that they are decaying. In this case, they are not safe to eat.

3. Foul or Off-Putting Odor

Detecting bad blueberries can also be done through foul or off-putting odor observations. Fresh and ripe blueberries have a dominant sweet,  fruity with melon hints produced by several volatile compounds, such as esters and alcohol.

However, as the storage period progresses, the scent will change.

The noticeable shift in the odor is also influenced by storage temperature.

Given the fact blueberries are cold fruits, storing them at room temperature (around 25°C) makes them ripen faster. Though it seems good news, the process also leads to quick decomposition.

Overripe blueberries smell sour, like vinegar, and rancid due to excessive sugar breakdown. To avoid this, you must provide proper preservation techniques to prolong their shelf life.

We will talk about it later on in the next section!

4. Visible Insect Damage

Identifying rotten blueberries includes several evaluations, including visible insect damage.

As soft fruits, blueberries are susceptible to pests and diseases. You’re not the only one with blueberries as your favorite fruit. Those culprits also enjoy sucking on sweet blueberry juices.

The berries emit sweet scents that lure the insects to feed on them.

how to tell if blueberries are bad
Visible Insect Damage

Apart from insects, wildlife such as birds and squirrels also love to snack on berries.

Generally, farmers will spray pesticides to get rid of those bugs. However, the foes can sometimes escape the pesticides and infect the fruits, leaving scars and damage on the skins.

This is detrimental, knowing that bruises can increase the risk of fungal and bacterial infections, leading to decayed blueberries.

In addition, some insects, like the blueberry maggot fly, may lay their eggs under the skins of ripe blueberries. Hence, you can use the pest damage indicator as a blueberry freshness test in detecting bad blueberries.

Touch The Blueberries

Now that you learn about detecting decayed blueberries and the possible causes of the deterioration, it is time to broaden your insights into evaluating the quality of blueberries.

Like we have discussed earlier, bad blueberry identification begins with physical observation.

You can examine the texture by touching it and check whether or not there are molds, insect scars, and slimes from the bacterial infection. Let’s have a look step-by-step on how to check if blueberries are spoiled below!

1. Assess The Texture of The Blueberries for Signs of Softness or Mushiness

Let’s start by detecting decayed blueberries by their textures! Healthy and fresh blueberries have a firm but delicate texture with a smooth skin surface covered with a thin layer of white wax.

Besides, they have deep purple with blue tones, which indicates that the fruits are rich in antioxidants.

Assess The Texture for Signs of Softness or Mushiness
Assess The Texture of The Blueberries for Signs of Softness or Mushiness

Nonetheless, if you feel the surface of the blueberries soften, you should be aware of decaying.

In general, the softening texture will be followed by juice leaking. Also, observe whether or not there are bruises around the soft skin.

Any scar can cause a faster ripening process due to the massive production of ethylene gas. Besides, it triggers microorganism infection and pest invasion, making the decomposition process go faster.

2. Check If The Blueberries are Slimy or Sticky to The Touch

After identifying rotten blueberries from the textures, you can move on to observing the juices.

As we said before, softening surfaces with surrounding scars will eventually spill the blueberry juice. If the juice appears watery, it is likely to have no or yet microorganism infection.

Nonetheless, slimy or sticky blueberry tells you that yeast rot infects the berries through the bruises.

Generally, the culprit behind this issue is sporadic post-harvest yeast called Aureobasidium pullulans (yeast rot), making the berries get wet, mushy, slimy, and collapse quickly.

And when that happens, you can do nothing except remove the berries from the storage because the infection may spread.

You might also like:

Blueberries Proper Storage Technique

In addition to giving you tips on how to tell if blueberries are bad to eat, we also include some methods on preserving your precious berries.

Considering their delicate nature, proper storage techniques are crucial to maintain their quality, including taste, texture, and aroma. Without any further ado, let’s get into the tips!

Rotten Blueberries Without Proper Storage Technique
Rotten Blueberries without Proper Storage Technique

1. Proper Storage Techniques to Prevent Blueberries from Going Bad

No matter how you have your blueberries, whether you pick them from your fields or buy them at stores, you must know how to store them properly to extend the shelf life.

It is vital since blueberries are susceptible to physical and chemical changes during the storage. There are two common methods to preserve blueberries, so you can enjoy them longer.


Fresh blueberries last only 2-3 days at room temperature (approximately 25°C) after harvesting. That short shelf-life is understandable, knowing blueberries have soft textures with pores that make them risky for biological and physical contamination.

For that reason, many keep them in the fridge to prolong their shelf life for up to 10 days.

However, some mistakenly keep the berries in the refrigerator without additional treatment prior to storing.

As a result, the berries will decay in less than a week. So, here are some tips for refrigerating your blueberries so you can enjoy them longer:

  • Do NOT wash the berries. Blueberries have pores that will absorb moisture. It can lead to softening textures and invite microbial infection since the fridge temperature is only around 5°C. Besides, the white wax that serves as a barrier for contamination will be removed if you wash them.
  • Place a paper towel in the container. It is beneficial to remove excess moisture during storage. Remember that blueberries are still “breathing” though you have harvested them.
  • Get rid of bad blueberries from the container. Like humans, the rotten berries are infectious. So, take your time to observe and remove them before storing the rest in the fridge.
  • Do NOT keep them in an airtight container. It will trap the moisture which will make your blueberries rot quickly. Instead, choose a bowl or open container to store them.


If you harvest or purchase your berries in the spring or summer and want to enjoy them in the winter, then freezing is the best bet you can do.

Unlike refrigerating that will keep your berries for up to 10 days, frozen berries will last for months, even a year! Here’s a quick guide to keep your favorite blueberries in the freezer for an extended period:

  • Do NOT wash your blueberries before freezing! It will add more water that will later turn into crystal. This crystal may damage the structure of your berries, leaving them mushy once you thaw them.
  • Dry and store your berries using a rimmed baking pan. This method allows your blueberry to freeze fast and separately. Freeze them for around 30 minutes.
  • Transfer the frozen berries into sealed plastic bags. Then, write a date of when you store your fruits in the freezer.
  • Alternatively, you can try using a rimmed baking sheet and place aluminum foil on top of it prior to freezing. With this method, you should let the berries sit in the freezer for 6 to 8 hours.
  • To enjoy the berries, you can thaw them in a cold water basket. Don’t use a microwave if you don’t want the berries to get soft and mushy. We also recommend thawing the berries in the fridge to maintain the textures.

2. Ideal Temperature and Conditions for Storing Blueberries

You probably already know that these native North American fruits are like cold places to grow.

The optimum temperatures for growing blueberries are about 50°F to 90°F or 10°C to 32°C. Due to this fact, you must also pay attention to their nature to determine the ideal temperature and conditions to keep your blueberries.

Depending on the species and varieties, blueberries will likely remain in good shape for 10 days at max under 4°C – 12°C (393°F to 53°F) with 90-95% humidity. It is with a note that these fruits must be sealed in the cabinets to remove the air.

Ideal Temperature and Conditions for Storing
Ideal Temperature and Conditions for Storing Blueberries

However, we prefer to store blueberries at 0°C to 1°C (33°F to 34°F) to prolong the shelf life by up to 3 weeks with the same humidity level.

As for the freezing method, the best temperature to extend their shelf life is around -4°C or 24°F, followed by the exact moisture like the refrigerating method. With this condition, you will maintain their quality for months!

Even though freezing becomes one the best storing methods to maintain blueberries quality, it doesn’t mean the approach has no drawbacks. If you freeze the berries beyond the tolerable temperatures, they may experience freezer burn.

Freezer burn happens when the fruits come in contact with air during the storage.

Some symptoms of freezer burn include discoloration and changes in textures (soften). Though they are safe to eat, the physical appearance is not preferred by consumers.

3. Tips for Extending The Shelf Life of Blueberries

Aside from acknowledging how to tell if blueberries are bad to eat, we assume you know that blueberries have a short shelf life. It is due to their natural characteristics: soft texture, porous, high moisture, and rich in sugar content.

Hence, it is our call to find a way to preserve the berries. Thus, they are edible for an extended period with good quality.

Considering this matter, we recommend you check on your blueberries once you buy or harvest them. Spot and remove the rotten or bad ones immediately to prevent spreading the infection to the rest of the batch.

Afterward, you can gently pat the berries using a paper towel to remove dirt and excess moisture. Don’t wipe the white waxy stuff, as it is an essential barrier against diseases and infection.

Extending The Shelf Life of Blueberries
Extending The Shelf Life of Blueberries

Next, transfer them into containers. Choose the open one as the airtight container will lock the moisture from blueberry transpiration, leading to rotting.

You can also use vacuum seal bags to remove the water and, thus, extend the shelf life.

In addition, it is recommended to use a single layer of a rimmed baking sheet or pan to freeze them separately. It also allows the berries to freeze faster, preventing lysis caused by broken cell walls.

This lysis, if it happens, can change the texture of the berries to be softer.

Regarding thawing, we strongly encourage you to thaw using the fridge. It may be slower than submerging the berries in cold water. But this method allows you to enjoy berries with similar textures to fresh ones.

Also, you can easily store them back in the freezer without concern about their quality.

Final Thought

No wonder blueberries are expensive. Apart from their maintenance, which requires extra effort to deter pests and diseases, harvesting, transporting, and storing them also requires specific methods. These delicate fruits only last 2-3 days at room temperature, making them extremely prone to decay.

How to tell if blueberries are bad to eat can be observed through some signs of deterioration, including softened textures, off odor and flavor, discoloration, mold growth, and insecticidal damage on the skin and flesh.

You can prevent this by storing blueberries in the refrigerator or freezer, depending on your need.

If you wish to consume them later, freezing is the best storage method. Nonetheless, some pretreatments, like removing the bad ones and dirt, are necessary to ensure your berries remain in good shape and quality despite staying in storage for longer.

Latest Posts:

FAQs (Frequently Asked Questions)

Why do blueberries go bad so quickly?

Blueberries spoil quickly due to their high moisture content, soft texture, and porosity, which make them susceptible to absorbing moisture.

The combination of moisture and sugar content in blueberries promotes mold growth and bacterial contamination, leading to spoilage signs like discoloration, mold, mushiness, off-flavors, and odors.

Is it OK to eat bad blueberries?

No, it is not OK to eat bad blueberries, especially if they are mushy and moldy, as this indicates a high risk of food poisoning from mold spores. Only blueberries without off-flavors, odors, fungus, or other spoilage indicators might be considered safe to eat.

Is it safe to eat blueberries that are not sour?

Yes, it is safe to eat blueberries that are not sour, as long as there is no visible mold or signs of spoilage. However, if the berries taste bitter, it’s advisable to spit them out, as this could indicate spoilage.

Is it OK to eat the white stuff on blueberries?

Yes, it is OK to eat the white stuff on blueberries if it’s the natural, waxy bloom that acts as a protective barrier. However, if the white substance is fluffy and found on berries in storage, it likely indicates mold, and those blueberries should not be eaten.

How do you know if blueberries are good to eat?

Blueberries are good to eat if they have a white waxy coat, no bruises, and no juice leakage in storage. Check for signs of spoilage like softness, shriveling, or white fluff, which indicate mold and mean the berries are not safe to consume.

Leave a Comment

Your email address will not be published. Required fields are marked *