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How much moisture is enough to get the bugs going?
This question is based on pure curiosity…not something I would EVER consider.
I see the mommy bloggers using ghee in some of their anhydrous projects. My research would indicate that .3-.4% water still remains in ghee. Assuming they added it to a project that contained no additional water….would this end product be safe (without adding a preservative)? Bottom line…at what point does an anhydrous product need to be preserved (moisture content)?
Logically…I would think any amount?
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7 Replies
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I believe bacterial contamination has to do with water activity, not a water amount. I am not an expert on the subject, and I wonder what is the water activity in an anhydrous system?
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I was thinking there is a small amount of water in butter, but you can leave it at room temperature. It will go rancid, but that is another mechanism.
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Syl said:I believe bacterial contamination has to do with water activity, not a water amount. I am not an expert on the subject, and I wonder what is the water activity in an anhydrous system?
This is a good point, but I would have to think the quantity of water is one of the biggest drivers of water activity, no?
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I agree, but we are talking about anhydrous projects. At very low concentrations, can water have low activity in a fatty acid environment? Do you need a preservative for your anhydrous projects? You can find many foods that contain a low amount of water that can be preserved with sugar and salt because they bind the water.
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Some water must be present but the % doesn’t necessarily control. Water condensing, taken up from the air (anhydrous powders in a humid bathroom) or isolated in droplets can support growth.
The limiting factor for water if present is water activity (Aw) as Syl noted - and for cosmetic preservation purposes that’s about 0.7 (70% relative humidity). Aw is a function of dissolved solids in water - don’t know ghee. For perspective - 67% sugar (sucrose) would offer an Aw ~.86.
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Ghee is heated and dehydrated butter. The result is minor amounts of dissolved water in lots of fat. On one hand, that water is soaked up by fat through a process called swelling, the water molecules aren’t really free. And on the other hand, butter contains short to medium chain fatty acids which show some antimicrobial activity. Alsongside all the fat comes a bunch of water soluble stuff which reduces water activity within ghee even more. Likely, most microbes within the fat are cooked dead too. That’s why ghee stays fairly safe (until some fat eating microbe comes along). Cosmetic ghee would/should probably be preserved but more likely goes rancid faster than the bugs can grow.Imagine, water is one of the main contaminants in raw materials… sometimes it’s just a nuisance, sometimes your stash will putrefy. -
Typically if water content (in the formula) is less than 5%, you do not need preservative. In another words, available water (aw) should be <0.6.
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