In case you're wondering if Amish friendship bread -- which stays outside the fridge for days at a time, and contains milk -- is safe to eat, worry no more.
As long as there are no obvious signs of mold or bacteria, like strange colors or smells, then the mix should be fine. (It should have a tangy smell.) Actually, the fact that the mix is kept outside of the fridge is what allows the fermentation process (which is necessary because the mixes usually contain no yeast) to occur. Because the mixture is so acidic, it kills a lot of the bacteria, and if there is any remaining, it will get killed when you bake the bread.
Pioneers moving out West in the 1800s relied on these mixes while they were traveling; they often couldn't buy yeast.
As someone who recently tried friendship bread baked by a co-worker, I can tell you, it tastes great. But in case you're still worried, you can put it in the fridge after about 3 days (enough time for the fermentation to start).
There's even a whole book on the safety on bacteria in food, called Nourishing Traditions, by Sally Fallon, that explains all this in more depth -- it's just our obsession with all things anti-bacterial that's keeping us from enjoying some of the finer things in life. (I would group Amish friendship bread with those finer things.)
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