The Hidden Danger of Mold in Tomato Paste: Why You Should Never Just Remove the Surface Layer

Although many people sometimes scrape off the visible layer of mold from stored foods such as tomato paste or jam and continue using the rest, experts strongly warn against this practice. They emphasize that mold can spread deep into the food, accompanied by the growth of harmful bacteria. Food safety specialists point out that mold can produce toxic chemical compounds known as mycotoxins, which may cause poisoning and, in severe cases, even death.

Serious Health Risks of Mold

Mold poses the greatest threat to soft foods such as fresh fruits, jams, tomato paste, soft cheeses, bread, peanut butter, yogurt, and cream—because mycotoxins can easily penetrate the food.

In contrast, with hard foods like aged cheese, it is sometimes possible to cut away the affected part and safely keep the rest.

Tomato paste is one of the most widely used ingredients in kitchens worldwide, valued for its rich flavor and color. However, some may notice a moldy layer forming on the surface of the paste after opening the can and storing it in the fridge. Many simply remove the visible mold and continue using the rest—yet, according to Healthline, this common habit is both wrong and dangerous.

Experts explain that even if mold appears only on the surface, its microscopic roots can extend deep inside the food, creating an ideal environment for bacteria to thrive. Among the most dangerous are those that produce mycotoxins—toxic compounds that can cause food poisoning or, in large amounts, even death.

Studies show that mycotoxins can cause severe health issues such as vomiting, diarrhea, and acute liver diseases. Over time, they can also weaken the immune system. The main problem is that mycotoxins are invisible to the naked eye—meaning that even when mold isn’t visibly prominent, contamination may already have spread.

What Is Mold, and Why Does It Appear in Tomato Paste?

To understand its danger, we must first know how mold forms. Mold is a type of microscopic fungus that develops when food is exposed to moisture and air for extended periods.

In tomato paste, this process begins the moment the container is opened or when a damp spoon is used. This introduces moisture and bacteria, gradually lowering the acidity of the paste and turning it into an ideal environment for fungal growth. The natural sugars in the tomato paste act as “fuel,” helping the fungi multiply and spread through the inner layers—even without visible signs on the surface. This is when the danger begins.

Why You Shouldn’t Just Remove the Mold and Use the Rest

While scraping off the moldy part might seem reasonable, it actually opens the door to serious health risks. Mold doesn’t stay on the surface—it sends out microscopic filaments that spread throughout the paste, carrying moisture and gases that alter its internal structure.

So, does mold cause poisoning? The answer is yes. Mold produces tiny compounds called mycotoxins—invisible and odorless substances that can disrupt digestion, damage the liver, and weaken the immune system over time.

What Happens Inside the Jar After Mold Appears

Once mold starts growing on tomato paste, what you see on the surface is only the beginning of a complex process inside the jar. The internal environment changes: acidity decreases, organic matter begins to decompose, and this imbalance creates a perfect breeding ground for both fungi and bacteria.

These processes trigger chemical reactions that cannot be reversed by heating or cooking.

Dangerous Chemical and Biological Changes

Inside the container, sugars and proteins begin to break down, releasing carbon dioxide and organic acids that alter the smell and taste of the paste. As decomposition continues, internal humidity rises, creating slight pressure that can cause the jar to swell or leak. Some fungi even produce enzymes that break down the tomato itself, turning it into a toxin-rich substance that cannot be made safe again by boiling.

At this point, the only solution is to discard the jar completely.

The Right Way to Store Tomato Paste After Opening

Proper storage is the first line of defense against mold. Even the smallest amount of air or moisture can speed up fungal growth. To preserve your tomato paste and keep its fresh flavor:

1. Store it in a clean, airtight glass jar.

2. Cover the surface with a thin layer of vegetable oil to block air exposure.

3. Refrigerate immediately after each use.

4. Always use a clean, dry spoon.

5. Consume within 3 to 5 days.

6. For longer storage, freeze it in small cubes.

6 Warning Signs That Tomato Paste Has Gone Bad

Even with proper storage, tomato paste can still spoil due to temperature changes or air leakage. Ignoring early signs often leads to rapid deterioration. Here are the key indicators that your tomato paste is no longer safe to use:

1. Dark or grayish color – signs of oxidation and loss of natural quality.

2. Sour or unusual smell – indicates bacterial activity or decomposition.

3. Water separation or sticky texture – a clear sign of mold growth.

4. Swollen or leaking container – caused by gas buildup from microbes.

5. Sour or bitter taste – shows that acidity has changed.

6. Visible mold patches – even small spots mean the paste is contaminated.

A Final Reminder

Tomato paste may seem like a simple pantry item, but it’s actually one of the foods most prone to hidden spoilage. Mold doesn’t just affect appearance—it alters the food’s composition and releases toxins that can’t be seen or smelled.

Always handle it carefully: store it properly, watch for any change in texture, color, or smell, and remember—a safe kitchen depends not on luck, but on awareness.

Even small details, like using a dry spoon and sealing the jar tightly, can make the difference between a healthy meal and a hidden hazard.