Wednesday, May 9, 2012
Honey: Nature's tastiest humectant?
So what's the deal with honey? If you want to know about how bees process it and stuff, I really recommend reading the Wikipedia entry on the topic or the book A Book of Bees, which contained such interesting tidbits such as the fact that a bee makes about 1/12 tsp of honey in a lifetime and that a cup of bees contains about 300 bees. (If you do the math, you realize that a cup of bees will make a cup of honey!)
The chemistry of honey is interesting. It's what is called a supersaturated solution of sugar, meaning that it contains more sugar than it should. This is one of the reason we see crystallization of honey - at room temperature, it's lower than its melting point of 40˚ C to 50˚C (104˚F to 122˚F), so we see the crystals forming. The higher the humidity, the easier honey flows. (You can heat your honey to remove the crystals, if you want.)
Honey has a water activity of 0.6 - it has very little available water for organisms, which means most of them won't grow in it...but dormant Clostridium botulinum spores can live in it, which is why you don't want to feed it to small children or the immune suppressed.
An aside on water activity...Water activity is defined as the water requirements for survival or growth of microorganisms. But water activity is not the same as the amount of water in a product. In some cases, the water is bound to other molecules (say, Epsom salts) and isn't free for usage by the microbes. In other cases, the water is bound by humectants like sorbitol or glycerin (anywhere from 10% to 20% will bind water). So water activity is actually a measure of the amount of free (unbound or active) water molecules present in our products. Water activity increases or decreases with increases or decreases in pressure and temperature. pH also plays a role.
When we dissolve a solute like salt or sugar into water, the amount of water available to our beasties decreases so we say the water activity is reduced. Reduce it enough, and you've got an environment inhospitable to microbes. If the microbes don't have enough water, they die or go into a dormant state. "Bacteria usually require at least 0.91, and fungi at least 0.7" (from Wikipedia). (Check out this post on osmosis!) This why we can preserve jams with sugar and fish with salt.
And honey can be a preservative to things that are stored in it. But once you expose it to humidity, water, heat and/or possibly light, that preservative ability is easily destroyed. The preserving qualities could be thanks to the hydrogen peroxide released when honey is is diluted, the phenolic compounds that behave as anti-oxidants, the things that help chelate iron, or the low water activity. (This is tomorrow's topic, so look for more evidence then!)
Water is not honey's friend! "Water migrates from areas of high aw [water activity] to areas of low aw. For example, if honey (aw ≈ 0.6) is exposed to humid air (aw ≈ 0.7) the honey will absorb water from the air." (Wikipedia). This explains how honey is a humectant and why it won't work as a preservative!
Why would we consider using honey in our products? I like to use it as a humectant and it definitely has label appeal! Think how lovely it sounds as a product name. Orange blossom and honey lotion or oatmeal, milk & honey lotion or something else & honey lotion. It sounds just lovely.
Is it a great humectant? It's okay...but when we consider the other humectants to which we have access and the fact that honey decays quickly when exposed to water and heat, it's not going to be the best choice for a humectant. I've used it with other ones - generally, honey plus sodium lactate or sodium PCA because it's just too sticky combined with glycerin - and it does bring a little something to the party.
Join me tomorrow as we take a look at some of the studies on honey!