We all know that getting your five a day is important, so it’s seriously disappointing to pick up a tomato, only to find it covered in a thick layer of what looks like mold.
So, what can you do? Is it still safe to eat a tomato with a little mold on it, what type of mold grows on then and how can you prevent it from happening again?
In this article, we will be answering all these questions and more, so for all you need to know about mold growth on tomatoes, keep reading!
Tomatoes with signs of mold or mildew growth should be discarded, as ingestion can cause gastrointestinal discomfort as well as causing potentially serious allergic reactions in those sensitive to mold and its spores. Cooking the tomato may kill the mold, but the toxins it creates can remain harmful.
Why do tomatoes become moldy?
Tomatoes are stored in high humidity environments, between 85-95%, and kept at a temperature range of between 58-60 degrees Fahrenheit for mature green fruits and 48-50 degrees Fahrenheit for pink fruits.
The temperature the fruits are stored is on the cusp of the ideal range for mold to begin to grow rapidly (between 60-80 degrees Fahrenheit), so any fluctuations in temperature can allow mold to begin to spread.
Damage caused to the skin of the tomato or through the stem site (the area where the tomato used to be attached to the plant), are the most likely places for mold to begin to develop, as it allows access to the nutrients and high moisture levels required by mold and mildew.
This damage most often occurs during harvesting and transportation, either from the farm to the storage/sale location or from the grocery store to the purchaser’s property.
Tomatoes can become moldy very quickly under the correct circumstances due to their high moisture content. The moisture combined with nutrients within the flesh of the tomato makes for the perfect place for mild to set up home as long as the temperature is warm enough.
Once the fruits are purchased and taken home, maintaining the ideal storage conditions is important to prevent mold growth and rapid spoiling.
What kind of mold grows on tomatoes?
There are three types of mold that are commonly found growing on the fruits of the tomato plant, or on its leaves, these are:
White mold (Sclerotinia sclerotiorum)
Gray mold (Botryotinia fuckeliana)
These strains can affect both the plant and its fruit, so let’s take a closer look at each of them so you can help to identify which it is that you may be dealing with.
Powdery mildew is a fungal disease that can affect many parts of a plant, including its leaves, stems, and fruits. It creates a white powder-like substance from which its name is derived and can spread rapidly if the correct conditions are met.
Interestingly, the type of powdery mildew that affects tomatoes rarely creates the dusting of white powder you would associate with this fungus, instead, small yellow patches may be seen on the leaves of the plant.
Sustained warm temperatures between 60-81 degrees Fahrenheit, and shady areas create the ideal growing conditions for powdery mildew, with its spores easily able to spread in drier climates. Unlike many other types of fungi, powdery mildew does not require a high-humidity environment and can grow successfully with lower ambient moisture.
Despite its unpleasant appearance, powdery mildew is rarely fatal to tomato plants, but it can cause yellowing of the leaves which may cause them to dry up and fall off, leaving the fruits exposed to potential sun damage.
White mold more often than not appears on the tomato plant, rather than the fruit itself. Sclerotinia sclerotiorum is a type of pathogenic fungus that can cause damage to leaves and stems, whilst causing white cotton-like growths.
White mold (or stem rot as it’s sometimes called) requires sclerotinia inoculum to be present within the soil surrounding the plant, a warm and humid climate, and plants that have recently begun to flower in order to spread effectively.
After the ambient temperature reaches 50 degrees Fahrenheit or greater, the fungus begins to germinate and spread. This usually occurs in the spring months of the year. Once the spores germinate, they spread onto nearby plants, including tomatoes.
Grey mold is caused by the fungus Botryotinia fuckeliana, which is a formidable fungus that can cause serious damage to tomato plants, appearing as a grey-to-brown velvet-like growth that can wilt leaves and damage stems and fruits.
Grey mold is most commonly caused by high humidity and warm temperatures and grows more efficiently in stressed plants or fruits and leaves with wounds.
Are the molds dangerous?
Unfortunately, many of the strains of mold that can affect either the tomato plants or its fruits have the potential to cause harm to humans.
In some cases, people with healthy immune systems may suffer from very few (if any) symptoms from the forms of fungi described above, however, for people with suppressed immune systems or allergies, coming into contact either through inhalation, ingestion, or via touch can cause potentially serious symptoms, including:
- Respiratory infections
- Lung diseases
- Gastrointestinal discomfort
These are just a few of the potential symptoms you could face when dealing with mold and its spores. And it is for this reason that it is best to keep as much distance from mold on tomato plants as possible, as it is often very difficult to accurately determine which strain you are dealing with as well as its potential toxicity levels.
What does mold on a tomato look like?
Typically, gray or white mold on the fruit of a tomato will have either white or grey powdery to velvet-like growth. It often appears as small specs of gray or black spots on the stems, leaves, or fruits of plants and quickly progresses, causing the area it has affected to begin to rot.
Powdery mildew on the other hand is often difficult to spot, as the specific strain that affects tomato plants does not create the telltale white powdery substance other strains of powdery mildew do. Instead, the only symptoms of powdery mildew you may spot are gradual yellowing of the leaves and stems which eventually dry up and die.
Can you cut off mold on a tomato?
It is never advisable to simply cut off the moldy part of a tomato and consume the rest. This is because the mold that is visible to the naked eye is only a small fraction of the infestation.
Once established, mold has deep roots which go beyond the surface mold you can see, so cutting off the visible mold will still leave the roots of the mold, and quite possibly the toxins it has created within the rest of the fruit.
Upon eating even small amounts of mycotoxins (the toxins released by mold strains), symptoms can arise, certainly in individuals susceptible to them, but occasionally even in otherwise healthy people.
If one tomato in a pack is moldy should you throw the rest away?
Much as it may seem incredibly wasteful, should you return home from a trip to the grocery store to find a moldy tomato within a punnet, the rest should be thrown away also.
This relates back to the previous statement about mold not always being visible to the naked eye. Mold and its spores can quickly spread from one infected fruit to the next, without any visible signs of infestation in the early stages.
Washing the tomatoes may help to remove some of the spores that have settled on the skins or within the stem site, however, it is very difficult to tell if any mold has already made its way into the flesh via any wounds that are too small to be seen.
It is for this reason that we suggest you throw the whole punnet away instead of trying to “rescue”, any remaining tomatoes.
Can you eat moldy tomato after it’s been cooked?
Accidents can happen, and it’s entirely possible that you could have hastily prepped some tomatoes for a meal without noticing they had mold growing on them.
The heat from cooking can kill some strains of mold, but not all, and more importantly, the mycotoxins they create are not always destroyed by heat either, allowing them to continue to cause symptoms in people sensitive to them.
The number of spores you are likely to have accidentally ingested is of course, very low, so in the majority of cases, you will see little to no symptoms. However, if you do have allergies or start to feel unwell after eating food you believe to have contained mold or fungi of any kind, you should seek medical attention.
How to store tomatoes to prevent mold
The ideal way to store shop-bought tomatoes to prevent molding depends on which stage of their lifecycle they were sold.
For underripe tomatoes, storing them in a dry location outside of the fridge, at room temperature, and preferably out of direct sunlight will allow them to ripen naturally. After ripening they should be transferred into a refrigerator.
Ripe tomatoes should be kept in a refrigerator, stem side down at a temperature between 44-50 degrees Fahrenheit and preferably in the lower humidity areas of the refrigerator, such as the fruit labeled crisper drawer.
How long does it take for tomatoes to mold?
During the cultivation stage, mold can grow and infect tomato fruits within only 4-5 days. Purchased items will last several days to one week before going bad in the fridge and start to show signs of mold growth.
Are white spots on tomatoes mold?
Oftentimes, the white marks visible on the surface of tomato skins are the result of sunscald, which comes from being in direct sunlight for long periods of time.
These marks can often appear in shades of white or grey and may at first glance appear to be mold.
Another potential cause of white spots on tomatoes could be bacterial cankers, which have the appearance of small black dots surrounded by a white circular pattern. It is an infectious disease of tomato plants and is not easily controlled, but is not a strain of mold.
Tomatoes can begin to mold very quickly if not stored correctly, powdery mildew and white and gray molds can infect the plant itself as well as the fruits of the tomato plant. In very small quantities, exposure to mold from tomatoes is unlikely to cause symptoms in healthy individuals, but people with allergies or suppressed immune systems should keep well clear, as they could cause allergic reactions and serious symptoms.
Storing ripe tomatoes in the lower humidity areas of a refrigerator at a temperature range between 44-50 Fahrenheit is the best way to prevent mold growth.