odd man out wrote:
Correct that the yeast grow better with oxygen but no alcohol is produced. Oxygen is needed initially to get the culture started. But there are lots of bad bugs that will live you n oxygen. That's what makes your food rot. Fermented foods were developed to preserve food. Of course there are lots of microbes besides yeast that are involved and the process is very complex. I read that in fermenting saurkraut, there are a whole series of microbes involved. The byproducts of the initial fermentation provides conditions so a second wave of bugs thrive. Then they make it favorable for the next, etc. Your ginger bug uses natural microbes from the ginger so there are probably lots of things in there. I made Kimchee a couple times. Once it came out great. I tried again and it was a total failure. What I should have done is to save some of the good batch to do innoculate the second. For most beer, you just want one strain of yeast so you set up the conditions to make your starter culture pure. Then you get your primary fermentation to start as fast as possible but it has to go anaerobic so the alcohol knocks out the unwanted bugs. The pH is also important. The beer should be slightly acidic. Under these conditions, bad bugs won't thrive. I think your recipe has lemon juice. I'm guessing that is there the acid.
Lost in the right direction.