When we refrigerate a something at 40˚F or 4.4˚C, we can stop the bacteria from multiplying, but we don't kill them (Click here for more information as it relates to food). The key is that the bacteria growth is only retarded, not stopped. This is why food can only be kept so long in the fridge before it needs to be thrown away. (Have we all had the wonderful experience of finding a piece of last week's chicken hiding behind the milk? Ick! No, well, I guess I was just a horrible housekeeper my last year of university!) If we want that food to stay better longer, we need to put it in the freezer. (Click here for more information on this topic!)
Let's say you make an amazing water-containing product and decide to not to preserve it because it's just for you or that you'll always keep it in the fridge. Even if you're scrupulous about taking it out of the fridge, squirting out a bit, then returning it to the fridge, the bacteria will still be growing. It might be slow, but they are growing. And there will come a point where your lotion is like last week's chicken and you can't use it any more (and no, I don't know how long...)
When you remove that product from the fridge, the bacteria will start to multiply again when it gets above 4.4˚C, which isn't that hard to do considering room temperature is around 18˚C to 20˚C. (You don't need the entire product to warm. If the surface gets warm and there's bacteria there, they'll be partying while their colder brothers are still chilling.) If you're taking that amazing conditioner into the shower and back to the fridge, imagine how warm it's getting in your bathroom!
No matter how obsessively clean we are in the workshop, there's always a chance of contamination. (Does anyone use a brand new bottle of distilled water every time you make a product?) This is the reason we use our preservatives. Not only will most of them prevent contamination in the future, but they will help us kill the nasties that might have been transferred into the product as we made it. If you aren't using preservatives, you aren't able to kill the contamination that might be in the product when we put it in the fridge, and those bacteria could eventually multiply. By using a broad spectrum preservative, we can prevent this! (Make sure you're using something that actually kills the bacteria. Something like sodium benzoate is a bacteriostatic, which will retard growth, but it won't kill it.)
Yeah, I know I harp on and on about this topic, but it's a vital one. And it's not helped by the deceptive labels that don't include preservatives on the list or hide them under other ingredients or the misinformation passed around by those who make products. Besides, it's a really interesting book that has me thinking before I go to sleep!
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