SCOBY buoyancy and oxygen level

[scobysurfer]

OK, so I just got several SCOBYs in the mail and this latest one just sank straight down after I put it in. Am I already off to a bad start here?

Also, I notice there are many discussions on whether to refrigerate or keep a SCOBY outside, but what about the oxygen level? Besides temperature, there's a big difference between sealing up a SCOBY in some Tupperware container or allowing it to get some O2 in a muslined jar. Any insight on the effects lack or oxygen?

 

[s0njas0n]

The ones I got sank and one is now floating (took 2 weeks) and my batches have been fine


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[cakeface]

mine always sink, but then a new baby will form on top, it will look kinda like a thin film at first and sometimes not real uniform. and bonus if you get a few bubbles in there, it's forming a bit of co2. don't panic if you see brown floating thingies, they are just bits of yeast and sometimes float to the top. always keep your jar covered with a cotton cloth, i use a rubber band to keep in in place, and keep your jar where it will get plenty of air but it doesn't like light (i use that same dishcloth to cover the opening and to keep the front of the jar covered - no closets.) don't refrigerate. 70-80 degrees is good, but cooler temps are ok, they just take longer to ferment.

 

[kyt]

The pellicle is made of cellulose, which is more dense than water and should sink. During formation it is possible for CO2 bubbles to get trapped, and this is what causes it to continue floating. If it sinks, don't fret, you'll get a new one shortly whether you want it, or not.

Don't use muslin, the weave isn't tight enough to keep out small flying pests. They will get in there. Something like a t-shirt or coffee filter is best. Just not something with so tight of a weave that ambient air can't exchange with the CO2 blanket on the surface. The bacteria use the oxygen in the air to convert the ethanol into acetic acid.
The yeast in solution will scavenge most of the O2 in the liquid. If you were to cut off oxygen from the surface completely, the aerobic bacteria will either convert to anaerobic, or they'll go to sleep. The anaerobic processes occur at a significantly reduced rate.