Why Doesn't Honey Go Off?



It is generally said that honey doesn’t ‘go off’.  

To back up this claim, it is often quoted that jars of (edible) honey about 3,000 years old have been discovered in ancient Egyptian tombs.  But is this true?  Can honey 'go bad'?

In actual fact, the story of the edible 3,000 year old honey seems to be nothing but an oft-quoted myth.

The story of the edible 3,000 year old honey seems to come from a misreading of a report in 1908 of the opening of the tomb of Yuya in 1905. 

Two alabaster jars were discovered in the tomb – one containing a rancid sticky oil that ‘resembled honey, but smelled and tasted of oil’; while the other contained ‘a liquid which was first thought to be honey, but was subsequently proved to be natron.’  So, in actual fact, the story does not 3,000 year-old honey at all!

Even so, many people do report consuming honey that has been left at the back of a shelf for 10 years or so – usually saying it has part crystallized and darkened in color, but is otherwise edible. 

So, why is it that honey can remain edible for so long – why does it not ‘go off’? 

comb honey on a plate - why doesn't honey go bad?

Why Honey Doesn't Go Off

The reason for honey’s longevity is due to its chemical composition. 

In short, there are three important characteristics of honey that retard microbial growth:

  • the low water to high sugar content; 
  • the low pH; 
  • the presence of hydrogen peroxide.

 

Low water to high sugar content

     

 

Firstly, in food science as ‘the water activity’.  This is a complex measurement, but in simple terms it is the amount of water in a foodstuff that is available to support microbial growth – higher ‘water activity’ levels tend to support higher microbial growth.  Honey has a water activity level that is too low to sustain bacterial growth.

Whilst Honey has a low water content of about 17%, it does however, have a very high sugar content – over 80% for most commercial honey, being made up of a range of sugar types, such as fructose, among others

Given the low water / high sugar content of honey, water from the bacteria will move (by osmosis) through their cell membranes from the area of higher water content (the bacteria) to the area of lower water content.  (Osmosis is the passage of water through a semi-permeable membrane from an area of high water concentration to an area of low water concentration.) 

So, if bacteria and fungi find their way into honey, water passes through their cell membranes into the honey, and thus they are dehydrated by the honey and unable to survive. 

The anti-bacterial properties of honey have meant that honey has been found to be effective, for example, in countering MRSA infection.

Low pH

Secondly, honey has a low pH.  The pH of honey is about 3.9 – making it quite acidic

Most bacteria thrive at a neutral pH (about 7), so the acidic nature of honey inhibits most bacterial growth. 


Hydrogen peroxide content

Hydrogen peroxide is also a potent inhibitor of bacterial growth, so the presence of peroxide in honey is also a contributor to its longevity, helping to ensure that honey does not go off.

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