Fermentation can be done in a variety of ways,
though generally at least for food purposes we'd like probiotic bacteria,
such as bifidobacteria and lactobacillus that are very beneficial to humans.
I've done a lot of fermentation, and have a small business doing fermentation, so do lots of research on it.
Vegan icecream yogurt recipe at the end!
Anyways enough intro, bifidobacteria, lactobacillus are anaerobes meaning they don't like oxygen, at most tolerating it.
wheras some detrimental bacteria such as candida yeasts and chronic-fatigue enterococci can use oxygen,
so the presence of oxygen in the brew or gut favours the "bad bacteria".
Bifidobacteria (good bacteria) is partciularly sensitive to oxygen so it's good to not only air-seal the brew,
but also to absorb the oxygen within the brew by adding antioxidants in the fermenting medium.
Studies have shown that using powerful antioxidants like EGCG in green tea http://www.ncbi.nlm.nih.gov/pubmed/22727242
especially potent from matcha green tea which is powdered form with ORAC over 1300 micromol per gram (compare to blueberries, just over 90 micromol per gram).
Since I'm big on permaculture I'm always wondering what a good temperate alternative is, and found that north american Staghorn Sumac is even more potent antioxidant with ORAC of over 1500 micromol per gram http://www.ncbi.nlm.nih.gov/pubmed/23411251
So I'm going to be harvesting staghorn sumac this year for sure to use in my brews,
Matcha tea is relatively expensive by comparison it is 10-15 cents a gram and has caffeine.
Omega-3's have also been shown to improve the viability of bifidobacteria, and how well it can adhere to intestinal walls,
so if you have a ferment that allows it like sourdough, or fermented beans can add some flax or chia seeds/oil to improve them.
Some people promote "open air" or aerobic fermentation though I believe that's generally a bad idea, since it simply allows yeasts molds and other aerobic contaminants to take root. Often the argument is that allowing the ferment to access the air is necessary to access the wild yeasts and bacteria, but truth is assuming the components of the brew haven't been sterilized they already have wild microorganisms. Also you don't really know what wild microorganisms are on it, and if they are even beneficial, so it's a good idea to at least have a base of ferments with microorganisms you know are beneficial.
I've acquired bifidobacteria strains, sold as babyFlora at the the real canadian superstore, though surely can be found in other places also.
I use it as a starter for my ferments, though have a variety of other strains I add depending on what I'm fermenting, like sourdough I add propionobacterium freudcherii for B12, and for yogurt can add in a probiotic capsule of lactobacillus.
I'm pesco-vegan so make vegan yogurt/ice cream, nowadays I use 1 cup adzuki-beans (high orac) and 1/4cup flax seed (possibly also 1/4cup pepitas or peanuts), anaerobically fermented for a day or two, then pressure cooked, manually food processed, add a can 400ml of coconut milk with 1/2 cup sugar, a gram of matcha and tablespoon sunflower lecithin as emulsifier, then anaerobically ferment (with bifidobacter etc) for several hours in a sealed masonry jar, refrigerate and viola! you have yogurt, can freeze with stiring every half hour for several hours for icecream.
Careful as the fermentation does expand the yogurt, makes 1Lt unfermented and 1.5Lt or more fermented, depending on time and temperature.