How do you know if something is spoiled?

In this brief guide, we will answer the question “What does spoiled food smell like?” and discuss some other signs of food spoilage as well. We will also tell you what causes food to spoil, give you tips on how to properly store food and discuss what happens if you eat spoiled food.

What does spoiled food smell like?

The smell of spoiled food depends on the kind of microorganism causing it and the type of food. For example, mold growth can give off a musty, earthy aroma while food that contains lots of fat will smell rancid and sour due to the fats getting spoiled in it (1). 

Yeast can produce sulfur-like smell. A surprising fact is that one bacteria namely Pseudomonas fragi has a strawberry type pleasant odor. It is the bacteria that spoils dairy products (2). 

The smell of food should be the same as it was when you cooked it or before you put it in the refrigerator.

While these smells are indicative of spoilage, it’s essential to note that some harmful bacteria may not produce noticeable odors, so it’s wise to consider other signs of spoilage (1).

What is the smell of different types of spoiled food?

The kind of food and the degree of deterioration both affect the distinct smell (1,3,4,5). 

  • Spoiled meat might smell sour or even rancid. 
  • When spoiled, dairy products can release a sour or rancid odor. 
  • Fruits and vegetables may smell rotten, soured, or moldy. 
  • Seafood that has been spoiled frequently smells fishy or ammonia-like. 
  • The smell of rancid oils or fats is distinct and disagreeable, resembling that of paint or stale crayons. 
  • Furthermore, rotting grains or cereals may smell musty or old.

What are some other signs of food spoilage?

You can tell if something is spoiled by looking at some features listed below. Most often, you will be able to tell that a certain food has spoiled just by looking at it. Other times, it may not be as easy to tell if food has spoiled because some bacteria do not change the way how food looks or tastes but it in fact is present. 

Let us look at some signs of spoiled food (6,7,8,9).


Spoiled food will have some discoloration on it such as black or bluish black or even brown. Now it could be because of some chemical reactions like in the case of apples or simply because of bacteria and its toxins.


Mold is almost always visible on food when it has spoiled. This type of spoiled food should be discarded immediately.


Changes in texture also indicate food spoilage. If you notice any slimy, gooey or soggy textures, throw the food out.


If all else looks fine visually, take a taste test. Test to see if it tastes the same or has the taste altered. Altered taste usually means spoiled food.

For example cream and yogurt taste sour when they go bad. So does the milk.


Frost on top of frozen food indicates freezer burn. Freezer burn alters the texture and taste of food. So frost is a sign that the food has gone bad.

Gas Bubbles

Gas bubbles spotted at the bottom of jarred or canned food that travel upwards is also a sign of spoilage. 

What causes food to spoil and have a bad smell?

Food can spoil and have a bad smell due to various factors. Microbial growth is a major cause, as bacteria, yeasts, and molds contaminate food and thrive in favorable conditions of moisture, warmth, and nutrients (9). 

Temperature-accelerated enzymatic reactions also can cause food deterioration by dissolving food components creating bad smell. Fats and oils deteriorate due to oxidation, which is brought on by oxygen exposure (1). 

Abuse of temperature, insufficient cooling, or incorrect storage can hasten the deterioration of food by encouraging microbial development (3). 

Food deterioration can also result from the cross-contamination of microorganisms from raw or damaged food and by time alone since items have a finite shelf life (10). 

How to store food properly to avoid spoilage?

The key to avoid food spoilage and increase their shelf life is to store the food properly (11,12).

  • Keep the fresh uncooked meat frozen and always cover it with saran wrap or place it in zip lock bags to avoid contamination of other food products in the freezer.
  • Keep any fresh produce like fruits and vegetables separately in the produce compartment of the refrigerator. The gasses produced by them can cause other food items to go bad.
  • Keep the condiments in the pantry when unopened and place them in the refrigerator once they have been opened.
  • Do not wash fruits and vegetables before placing them in the fridge as mold can grow on them if they are damp.
  • Do not overcrowd the refrigerator. Overcrowding prevents cool air inside the refrigerator from spreading evenly across all food items.
  • Do not leave the refrigerator door open for longer periods of time to avoid temperature fluctuations inside the refrigerator.
  • Keep the dry spices in a cool, dry place, away from moisture, light, and heat. Keep them inside a drawer or in the pantry.

What happens if you eat spoiled food?

Eating spoiled food can lead to food poisoning, or foodborne illness. 

Foodborne illness is caused by bacteria, viruses, parasites, or their toxins. The most common pathogen causing food poisoning is Salmonella which is usually present in poultry and other dairy products (10, 13). 

The common symptoms of foodborne illness are (13):

  • nausea 
  • vomiting 
  • diarrhea, 
  • abdominal cramps 
  • malaise 
  • loss of appetite 
  • headache 

These symptoms can range from mild to severe. Severe conditions like food poisoning may include symptoms like fever, dehydration, and in extreme cases, organ damage (13).

Food contaminated by molds can contain mycotoxins that can cause allergic reactions or other adverse health effects (14).

If you suspect you have consumed spoiled food and are experiencing persistent or severe symptoms, it’s crucial to seek medical attention promptly.


In this brief guide, we answered the question “What does spoiled food smell like?” and discussed some other signs of food spoilage as well. We also told you what causes food to spoil, gave you tips on how to properly store food and discussed what happens if you eat spoiled food.


1. Takahashi, Y.K. et al. Detection and Masking of Spoiled Food Smells by Odor Maps in the Olfactory Bulb. The Journal of Neuroscience: The Official J Society for Neurosci., 2004, 24(40):8690-4.

2. Cormier, F., et al. Analysis of odor-active volatiles from Pseudomonas fragi grown in milk Champagne, and Andre Morin. J Agricul. and Food Chem., 1991 39 (1), 159-161

3. Addis, M. Major Causes Of Meat Spoilage and Preservation Techniques: A Review. Food Science and Quality Management, 2015, 41.

4. Barth, M. et al. Microbiological Spoilage of Fruits and Vegetables. USDA, 2009

5. Gram, L., Dalgaard, P. Fish spoilage bacteria – problems and solutions. Current Opinion in Biotechnology, 2022.

6. What are the signs of food spoilage?. USDA, 2023.

7. Does a change in color indicate spoilage?. USDA, 2023

8. Dilbaghi, N., Sharma, S. Food spoilage, food infections and intoxications caused by microorganisms and methods for their detection.  Food And Industrial Microbiology, 2007.

9. Nazah, J. Food Spoilage: Microorganisms and their prevention. Asian J Plant Sci and Rese. 2015, 5(4):47-56.

10. Carrasco, E., et al. Cross-contamination and recontamination by Salmonella in foods: A review. Food Research International, 2012, 45, 545-556

11. Food safety at home. Paediatr Child Health. 2008;13(9):783-790. 

12. Keep Food Safe! Food Safety Basics. USDA, 2016.

13. What You Need to Know about Foodborne Illnesses. FDA, 2022.

14. What are Mycotoxins?. USDA, 2018.