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This is a complex question because there are actually different strains of yeast depending on the region, different aging requirements/habits etc. I will say that biological versions of Sherry are arguably the most reductive wine on the planet b/c you have flor on top, dying flor hanging in strands from the raft and then a layer of lees on the bottom of the barrel - all of which are consuming oxygen. There is a form of oxidation going on but it's not affecting the wine as a whole (phenols etc), but rather just the ethanol which is a way that flor yeast creates acetaldehyde, the hallmark sour apple flavor of biological Sherry. Acetaldehyde can be converted to something called pyruvate which serves as a reserve energy source for the flor itself. This is why biological Sherry needs to be refreshed in the solera, to replenish oxygen, alcohol and other elements for the flor to succeed.
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Jason Heller My understanding is that they have done a lot of work on this over the last couple years and it was one of the reasons we thought to ask them to speak to the topic.
The Bollinger part was interesting especially since their Champagnes are the ones I find lots of bottles showing non age appropriate oxidation far earlier than anyone else.
I was having a discussion with some Somms about Fino Sherry, Vin Jaune, Vernaccia di Oristano and flor wines. Do you consider them reductive or oxidative? Because in theory they start off oxidative in the barrel before flor forms which protects the wine from oxygen.... as it ages for years in a porous vessel. Do you have any thoughts?