Refreezing Melted Ice Cream and Food Poisoning

Ice cream is a popular treat worldwide and has many fans among various age groups. According to reliable sources in 2024, the average global ice cream consumption per person was approximately 3 kilograms.
You have likely experienced noticing that the ice cream appears misshapen and sticky through the packaging when buying from stores, or if the packaging is transparent, you might see ice crystals on its surface. These signs likely mean that the ice cream has melted for various reasons, including a power outage at the store, and then been refrozen.
In addition to changes in shape and ice crystal formation, one of the common problems when ice cream melts and is refrozen is the change in its texture. Generally, ice cream is made from ingredients like milk, sugar, and cream. During the production process, through stirring and freezing, air bubbles are trapped among the ice crystals, resulting in a smooth and uniform texture. When ice cream melts, refreezing does not recreate the original crystal structure, and the ice cream's texture becomes grainy and unpleasant. This change occurs not only in dairy-based ice creams but also in frozen desserts like popsicles.
While changes in the appearance and texture of ice cream due to melting and refreezing do not pose a health or safety risk, the melting and refreezing of ice cream can create conditions for the growth of microorganisms.

 
The Risk of Microorganism Growth in Melted Ice Cream
In some cases, bacteria such as Listeria monocytogenes, Salmonella, and Escherichia coli may be present in ice cream. Although ice cream is usually made from pasteurized milk and is expected to be free of microorganisms, the pasteurization process may not always be performed correctly. For example, the temperature may not reach a sufficient level (around 72 to 75 degrees Celsius) or the required time (at least 15 to 20 seconds) may not be adhered to, resulting in some bacteria remaining in the milk. Furthermore, despite full adherence to hygiene principles during the production process, there is still a possibility of secondary contamination after pasteurization. This contamination can be transferred to the final product through various means, including processing equipment, packaging machines, and the factory environment. For this reason, ice cream is usually sent to food laboratories after production for health and safety testing and control.
Microbial tests for ice cream in Iranian standards do not include measuring the amount of Listeria monocytogenes, so the probability of this bacterium being present is higher than other bacteria. Additionally, even if none of these bacteria are present in the ice cream, the sealed packaging of the product may sustain minor damage during transportation or other stages, creating a small crack. In this case, bacteria dispersed in the environment can enter the product through these cracks, however small.
Some bacteria, such as Salmonella and Listeria monocytogenes, do not die in freezing conditions. If conditions become favorable for their growth, they can start to multiply. For example:

• If ice cream is left at room temperature and melts, any existing bacteria can start to grow, and their numbers may increase to the point where consumption can cause food poisoning. Generally, bacteria usually grow rapidly at temperatures above 4 degrees Celsius, so if ice cream is exposed to these temperatures and melts, the likelihood of it being contaminated with bacteria is high, and consumption is not recommended. However, if the ice cream has only been at room temperature for a short time or was mistakenly placed in the refrigerator and has only slightly softened, the likelihood of bacterial growth is lower.
• Power outages can also create conditions for bacterial growth. Generally, during a power outage, if the freezer door is not opened and closed frequently and the freezer is half-full, the food inside will remain safe for about 24 hours. If the freezer is completely full, this time increases to about 48 hours. To determine if the ice cream is safe to eat, it should be checked whether it has completely melted or not. If the ice cream completely melts during this time and no ice crystals remain, there is a risk of contamination and food poisoning, and consumption is not recommended.
   

This issue is more important for bulk ice cream that is usually not consumed in one sitting. This is because if the ice cream is left out of the freezer for a period each time it is served and then returned to the freezer, the risk of bacterial growth and subsequent food poisoning increases with each subsequent consumption.
Therefore, it is recommended that bulk ice cream be returned to the freezer quickly after each serving and that it not be left on countertops or tables. It is also essential to use a clean scoop or spoon to remove ice cream to prevent contamination of the remaining product.

Poisoning Caused by Listeria monocytogenes, Salmonella, and Escherichia coli Bacteria
Poisoning caused by Listeria monocytogenes, Salmonella, and Escherichia coli bacteria can have various symptoms and complications, including headache, fever, muscle pain, abdominal pain, and sometimes diarrhea and vomiting.
All these bacteria are more dangerous for vulnerable groups such as the elderly, children, pregnant women, and individuals with weakened immune systems, and can lead to more serious complications such as meningitis, blood infection, and kidney failure. Additionally, they can lead to miscarriage in pregnant women.

Final Word
When buying ice cream, pay attention to its appearance, and do not choose ice cream that shows signs of melting and refreezing. If the ice cream is not consumed immediately after purchase, it should be placed in the freezer at the appropriate temperature (minus 18 degrees Celsius) as soon as possible to prevent melting and the growth of microorganisms.
Given that all these bacteria can cause more severe symptoms and pose more serious health risks in vulnerable groups, it is recommended that these individuals exercise greater caution regarding the consumption of refrozen ice cream and preferably avoid it altogether.