If you’re new to fermenting, this question of “how do I know it’s fermenting?” probably crossed your mind the second you prepped your first ferment and walked away from its resting place. The signs vary from ferment-to-ferment, but there are some indications a ferment is active and healthy. You may see these signs, you may not. Either way, everything is ok! As long as your veggies are submerged in a brine and mold hasn’t grown, you’re on track. These signs may include bubbles from carbon dioxide, a cloudiness in the brine or the color fading from the vegetables.
If you REALLY don’t think something is fermenting, taste it after a couple days (not hours). If you don’t notice a subtle sourness developing and only taste salt, there are three things to consider: did you use salt with iodine, water with chlorine or vegetables loaded with preservatives? Iodine and chlorine will often inhibit the fermenting process, as will chemicals designed to preserve vegetables. Do you need to use organic? Absolutely not. Just make sure they're properly washed; it's very unlikely the issue is with your vegetables. If you haven’t done any of the above, just be patient! It’s possible cooler temperatures are slowing the fermenting process too, so keep tasting it and eventually you’ll notice a difference.
If that didn’t put you at ease, watch this video with fermentation expert and author Sandor Katz to learn more about what to expect (or not expect) during an active lacto-ferment.