Here's a good question sent to us via our Instagram page:
"How do probiotics survive the baking process in sourdough bread and how would the ones in apple cider vinegar stay alive unrefrigerated?"
The probiotics don't survive the baking process. Sourdough is made with a probiotic starter that contains beneficial lactobacilli, but once you stick the raw bread loaves into the oven, you in effect sterilize them, much the same as pasteurization does to milk.
That doesn't mean the bread isn't a worthy food. Before baking, the bacteria from the starter break down the gluten in the bread into its constituent amino acids (for those that wring their pearls over gluten).
Likewise, the bacteria produce acetic, propionic, and lactic acid, all of which reduce the availability of some of the starches to your digestive system, thereby lowering the bread's glycemic index. Lastly, the bacteria facilitates the breakdown of phytic acid in the bread, thus freeing up the bread's nutrients for digestion.
But as far as the finished product being a probiotic that benefits gut health? Nope. But it's a common misconception.
And What About ACV?
We also have to look at apple cider vinegar through the same microbiological lens. Most apple cider vinegar is, again, the product of a probiotic process; the bacteria works on the sugars found in apples and produced acetic acid, aka vinegar. Most apple cider vinegars in the stores, however, are filtered and pasteurized – they've had all the bacteria removed or killed. Consequently, they don't need refrigeration.
This type of apple cider vinegar is still useful in that taking a couple of tablespoons before a meal improves post-meal blood sugar readings by a significant amount.
Things are different with the unpasteurized version. It contains what purveyors of ACV call "the mother," which are the strands of protein, enzymes, and bacteria that give the product its murky appearance. Since the unpasteurized version contains these bacteria, it's thought by some to be a probiotic, but in truth, the bacteria contained in ACV have not, as of yet, been shown to survive GI transit.
Regardless, ACV with the mother does appear to be beneficial to existing bacteria, along with aiding in the digestion of proteins and fats (by stimulating the release of stomach acid).
This is the kind that should be stored in the refrigerator, as the low temperature will bring bacterial metabolism to a standstill, which is good. If you kept it at room temperature, the bacteria would continue to grow and multiply and "eat up" all the substrate in the vinegar until eventually they'd run out of food and die, ruining the apple cider vinegar in the process.
So, if you buy a bottle of unpasteurized apple cider vinegar, keep it in the fridge after opening it.