I have noted that many purchased food items in containers only require refrigeration after they have been opened, thus eliminating the vacuum seal. Air contains bacteria and fungus spores that enter the food container and if not refrigerated, the aerobic micro-organisms will proliferate, thus altering and rotting the food. The air also allows any dormant micro-organisms that survived the factory sterilization process already in the food to come back to life and proliferate.

However I do not understand why anaerobic bacteria, that don't require and cannot survive in air, do not proliferate and thrive in the vacuum sealed food containers. That plus the fact that we can leave already opened food items such as honey, jams, and peanut butter out of the refrigerator for weeks but they do not spoil.

  • 3
    $\begingroup$ I'm betting most of those foods are sterilized with heat either before or after being sealed in their packaging, similar to how you would can foods at home, just on an industrial scale. The vacuum seal functions to prevent microbial contamination of a sterile product, not just to prevent aerobic organisms from growing. $\endgroup$ – MikeyC Sep 3 '20 at 13:53
  • $\begingroup$ Honey, jams, and peanut butter each have antimicrobial properties on their own that help delay or prevent spoilage. $\endgroup$ – MattDMo Sep 3 '20 at 22:17
  • 1
    $\begingroup$ I think honey, jams, peanut butter antimicrobial properties isn't directly what prevents or helps with avoiding spoilage. It is their water activity being quite low. The water activity of peanut butter is typically 0.35, which inhibits the growth of spoilage and pathogenic microorganisms. $\endgroup$ – m4rio Sep 8 '20 at 19:24

Just adding a little bit more info taking from the answer above.

You got two types of anaerobes:

  1. Facultative anaerobe that makes ATP by aerobic respiration if oxygen is present. It can switch to fermentation or anaerobic respiration if oxygen is absent. Most common example of a food pathogen in this category: E. coli

  2. Obligate anaerobe which are killed by normal atmospheric concentrations of oxygen. Example: C. botulinum, which is mentioned in the answer above.

I am using C. botulinum as the example here because it is widely used in making HACCP (Hazard Analysis Critical Control Point) plans. These are plans with certain steps which make sure that what you're producing is proven safe for consumption.

Now, C. botulinum vegetative cells die in the presence of oxygen. The spores allow the organism to survive when there's lack of nutrients and/or oxygen levels are too high. The spores are also heat-resistant. C. botulinum cannot grow below a pH of 4.6, so acidic foods, such as most fruits, tomatoes, and pickles, can be safely processed in a water bath canner.

If the pH is above 4.6 there's usually a CCP (Critical Control Point) in the HACCP plan to make sure the product is pasteurized. For C. botulinum that is a kill step at 85°C for 5min minimum to destroy the toxin.

Another product example would be cold brew coffee. You need a certain % of dissolved O2 so that C. botulinum doesn't proliferate since cold brew coffee has a high pH (>4.6 usually).

Another problem with Reduced Oxygen Packaging (ROP), not related to anaerobic bacteria, is mold growth. To mitigate this some products might have the air present in the bag replaced with nitrogen then flushed. Nitrogen Flushes in ROP can reduce the rate at which mold can grow.

TL;DR: They do grow but there's certain steps each company needs to take to prove safety of their product before sale. If your HACCP plan accounts for C. botulinum you're sure to knock out a wide majority of obligate anaerobes (if not all) that could grow in your product.


I do not understand why anaerobic bacteria, that don't require and cannot survive in air, do not proliferate and thrive in the vacuum sealed food containers

They do. Vacuum sealing can prevent aerobic bacterial growth but does not prevent anaerobic growth.

Botulism is a particularly dangerous consequence. If food containing C. botulinum spores is sealed without being properly treated (usually by heating) or otherwise by being inhospitable to bacterial growth (often due to acidity or salt), dangerous botulinum toxin can accumulate and be dangerous or fatal when the food is later eaten.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.