A canna’ change the laws of physics

Scotty, The Naked Time, stardate 1704.3, Episode 7

Tell ‘em about the honey …

Posted by apgaylard on August 15, 2009

bigstockphoto_Jar_Of_Honey_With_Wood_Stick_3527559According to Annelie Whitfield, the presenter of Channel 4’s ‘The Kitchen Pharmacy” honey is hydrating.  In an episode featuring what she calls “anti-aging” treatments, she makes an “Avocado Face Mask” with avocado and probiotic yoghurt.  Finally she adds honey, saying:

“Honey […] is deeply hydrating and it really helps to get rid of any spots that you might have […]“

The video is available here.  Lots of things that Whitfield says strike me as odd.  This is just another small example.  So, is it strange but true, or just untrue?

For something to be hydrating it needs to contain water, and that water needs to be ‘free'; not bound up with other chemicals.  Now honey does contain water, around 17% by weight.  So, at face value, it might seem that honey could be hydrating.  However, if honey had a significant proportion of its water content available for hydrating human skin, it would also allow micro-organisms to grow in it.  Clearly, honey has a long shelf life, so this would suggest that the water in honey is not ‘free’.

There is a way to assess ‘free’ water content: a parameter called water activity (aW); it represents the amount of water a substance has available to hydrate other things.  It is defined by the ratio of the vapour pressure of water in a substance to the vapour pressure of pure water at a specific temperature.* For pure water aW =1 and for a substance with no ‘free’ water aW =0. 

So, where does honey fit on this scale?**  It’s quite easy to find some data to put honey into perspective as a potential hydrating agent.

Food

Water Activity

 

(aW)

Raw meat 0.98 – 0.99
Cheese 0.97
Cooked pasta 0.97
Bread 0.95 – 0.96
Aged cheddar 0.85
Preserves 0.8 – 0.88
Plum pudding 0.8
Dried fruit 0.6 – 0.76
Honey 0.6
Dry pasta 0.50
Biscuits 0.3
Milk powder 0.2
Instant coffee 0.2

Honey has low water activity, so little of its water is available for hydrating the things it comes into contact with.  That means it’s not “deeply hydrating” as Whitfield would have us believe.  Put it this way: bread, jam, cheese or raw meat is more hydrating.  But I guess that the facts don’t paint a picture pretty enough for this naturopath; honey has such a romantic, natural and healthy image. 

In the end, Whitfield’s claim is irrelevant as, in this case, the honey is added to a watery mix of avocado and probiotic yoghurt.  If this face mask is hydrating, it’s these ingredients that are responsible, not the honey. 

This is just another small example of the monstrous nonsense that this naturopath is allowed to present as fact by Channel 4; another salutary example of the critical thinking and research skills that bogus science degrees confer upon their graduates. 


If you think I have got anything wrong in this piece, please let me know. I try to be careful, but anyone can be mistaken. If you are right I will happily correct what I have written.

Other posts in the Kitchen Pharmacy series

Naturopaths angry up the blood

Cooking up arthritis treatments 

Notes

*See here and particularly here for a discussion of water activity.

**The values taken from here and here unless stated otherwise.

Edits

None yet!

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11 Responses to “Tell ‘em about the honey …”

  1. Zeno said

    There you go again. Using science to completely wreck the assertions of people who think they know what they’re talking about.

    Well done.

    • apgaylard said

      Thanks. If the BSc in naturopathy wasn’t featured and the language used didn’t resort to ‘sciencey’ expressions then maybe I wouldn’t be so interested. As it is, this seems to illustrate quite well some of the issues around anti-science BSc’s.

  2. budicius said

    I may be wrong but I heard once that bacteria is able to grow in Honey. I think some Honey manufacturing companies pasteurise their Honey to around 70 degrees celsius to kill off bacteria.

    • apgaylard said

      According to Martin Chaplin‘s website, “The absolute limit of microbial growth is about aW = 0.6″

      I wonder if some honey might have a bit more ‘free’ water and so be able to support microbial growth. These sorts of figures are only averages after all, and I have no idea what the variation around the mean might be. It may also be that they are worried about the potential presence of botulinum endospores

      Thanks for an interesting comment.

  3. brunton said

    Honey is usually hypertonic, which suggests that it would actually be dehydrating.

  4. budicius said

    Found some interesting news regarding Manuka Honey and its ability to kill antibiotic resistant bacteria. It may be used in the hospital setting although more research is needed to see how gut fluids affect its antibacterial properties.

    http://www.theaustralian.news.com.au/story/0,,25653017-23289,00.html

    Can’t find the journal article mentioned at the end of the news piece.

    • apgaylard said

      There has been, I seem to remember, a bit of discusion of the use of honey in wound care over the years. It’s not a topic that I’m familiar with. It looks like your news piece is picking up on this or this, or both?

  5. Excellent article – as always. Just wanted to let you know – speaking as a beekeeper of long-standing, honey is distinctly hygroscopic – i.e. it absorbs water from the surrounding atmosphere. This is important for beekeepers, because unless we make sure that honey is stored in airtight jars, it will absorb enough atmospheric water vapour to start fermentation, which ruins the honey. This is why bees cap their honey supplies with waz cappings – which do allow a very small amount of transpiration, but essentially the honey will last for several years ‘in the comb’. if left in an open jar it will become ‘runny’ and ferment withing a matter of a week or so. Honey absorbs water, it does not give it out.

  6. inlightpapers said

    First, aw values <0.60 are microbiologically stable – so honey, if it is at that aw, doesn't turn rancid.

    Second, since water has an aw of 1.00, it would follow from your analysis that water is perfectly hydrating. Yet clearly another factor needs consideration: evaporation. And a critical determinant of evaporation rate is vapour pressure, the very thing aw measures. Thus, a good humectant must balance aw and evaporation, by having a vapour pressure somewhere "mid-range".

    I do not know what the perfect vapour pressure of a humectant is, but I see no reason why honey should be disqualified.

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