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Signs of Food Spoilage

Understanding signs of food spoilage when preserving food by canning, drying, or freezing is crucial in preventing a foodborne illness.

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Updated:

May 2, 2025

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When food items undergo physiological, chemical, or biological changes, they can become inedible. One of the main goals when preserving food is food safety. Therefore, it is vital to stay updated on what the science says and use tested recipes. Preserving food begins by stopping the growth of microorganisms and inactivating enzymes. There are spoilage microorganisms like yeast and mold and pathogens like Clostridium botulinum, which cause botulism. Botulism can be lethal and can occur when food is improperly canned, preserved, or fermented. Enzymes are a natural component of food, and if they are active, they work by changing color, texture, flavor, and nutritional content.

Canning and Food Spoilage

When canning, meat and plain vegetables are low-acid food items. These foods support the growth of bacteria and bacterial spores due to the lack of acidity needed to inhibit that growth. You can avoid this by using good-quality products and by following proper canning procedures. We cannot see, smell, or taste pathogenic microorganisms but we can see or smell some signs of food spoilage. Canning failures like inadequate processing time and temperature can support the growth of molds, yeasts, and bacteria. Mold not only grows on the surface of food, but mold filaments grow down into the food. This means scraping surface mold does not eliminate mold or toxins that may have been produced. Therefore, throw away moldy food!

It is crucial not to taste food from a jar that shows signs of spoilage. Jars with unsealed lids, bulging lids, or a loose lid could indicate signs of food spoilage or the presence of pathogens. Other signs of food spoilage include rising air bubbles (gas), leaking, foam, foul odor, unnatural colors, sliminess, dried food on top of jars, and cotton mold growth (white, blue, black, green) at the top or under the lid (Blakeslee, 2021).

Fermentation and Food Spoilage

During the fermentation process for sauerkraut or pickles, it's essential to control and prevent any growth of yeast or mold. To avoid the growth of microorganisms, focus on salt concentration, keeping air off surfaces, and controlling temperature.

Freezing and Food Spoilage

Another way to preserve food is freezing. Freezing inhibits the growth of microorganisms that cause the food to spoil; therefore, freezing does not destroy them if present in food. If the food is not properly thawed, microorganisms like bacteria, yeast, and mold in the food can become active and cause the food to spoil or lead to foodborne illnesses.

Freezer burn occurs when frozen food gets damaged by ice crystal growth and dehydration, exposing food to oxygen. This can produce a loss in texture, color, and flavor. Physical signs of freezer burn are not the same as food spoilage mentioned above. Freezer burn appears as grainy, dry, and grayish/brown spots on the surface of the food. You will not become ill from eating a food item with freezer burn, but this product's desirability can be reduced. Carefully inspect frozen food products that could have accidentally thawed.

While it is important not to be wasteful of food, if we are not sure about a food item being safe to eat—then, when in doubt, throw it out.