You referenced oxygen transfer of the tank to be 2mg/l per month for the specified tank. I know this is a loaded question due to size, wood and other factors but do you have any idea transfer rate of a comparable size barrel?
Studies have been done over the years, Vivas 1997, The numbers range between 10mg/L/yr for old barrels, and 20 to 45mg/L/yr for new barrels. There are some discussions regarding how much oxygen is actually going through the wood and between staves, and how much oxygen is contained in new wood. The way Flextanks are made, the oxygen transfer rate is scaled up accordingly, so theoretically a 100gal tank provides the same 2mg/l/yr as does a 60gal tank as does a 30gal tank.
In your opinion is transfer in and out of the vessel or one or the other? This may go back to the first question and if the transfer rate is sizably different and is an in and out transfer I wonder how this would impact the wine differently.
Plastic is permeable both ways, but the rate and direction depends on molecule size as well as pressure or concentration difference across the wall; you have a constant supply of oxygen on the outside of the tank and near zero concentration in the wine, therefore the oxygen moves into the wine where it is immediately consumed. If the dissolved oxygen content of the wine starts to climb, then it needs to be removed from the tank or barrel, as this indicates that the oxygen is coming in faster than it is being consumed.
I agree all the cleaning, handling and storage benefits so my last question is the treatment of the headspace. How do you deal with that?
The tank needs to be topped up just like a barrel, I don't leave any headspace.
