What is an "Oxidative Yeast"?

[dantheman13]

I've seen this term used to refer to Brettanomyces, as well as "other yeasts". Here is one particular source from Wyeast, for example: http://www.wyeastlab.com/com-lambic-brewing.cfm

The Wyeast page seems to suggest that Brett is not in the category of "oxidative yeasts", but I have read other sources that do consider Brett an oxidative yeast. A homebrewer acquaintance of mine seemed to interpret an "oxidative yeast" as a yeast that will cause oxidation, and seemed to believe that the presence of Brett could explain oxidation in a beer. I am pretty certain that is not true (in fact every source I have read says that Brett helps prevent oxidation in aged beer).

So, what does it mean for a yeast to be an "oxidative yeast"? What sort of yeast genera/species/strains are "oxidative yeasts"? I can't seem to find a real definition for this on the internets or in Jamil's Yeast book.

Thanks,
Dan

 

[TimT]

They use oxygen, forming a pellicle to make use of of O2 present is likely a good indicator of it being an oxidative yeast. There is likely a lot of info about them on the web, but it will be associated with wine as, brett, candida, pichia and such are wine spoilage organisms.

 

[badlee]

I seem to remember reading that Brett can consume the compounds produced by oxidation and use them to further add to the "Bretty" character of the beer.

 

[Beernik]

They use oxygen, forming a pellicle to make use of of O2 present is likely a good indicator of it being an oxidative yeast. There is likely a lot of info about them on the web, but it will be associated with wine as, brett, candida, pichia and such are wine spoilage organisms.

This is what I'm coming up with on a google search. Basically, it has to live on a free surface to interface with oxygen.

 

[dantheman13]

This is what I'm coming up with on a google search. Basically, it has to live on a free surface to interface with oxygen.

So Saccharomyces, which needs O2 prior to primary fermentation, only consumes O2 that is present in the beer and not on the surface. So this makes it a non-oxidative yeast? That seems confusing to me.

Another difference between Sacch and Brett is that Sacch mainly consumes O2 prior to primary fermentation, while Brett will continue to consume O2 after primary fermentation is done. Does this have anything to do with the definition maybe?

As far as information on the web, I can't seem to find a real definition of the term, "oxidative yeast", although I have seen it used (sparingly). But the usage of the term never seems to indicate what exactly it means.

I sent Wyeast an email asking about this about a week ago. They haven't gotten back to me.

Thanks for your help, guys.

 

[Beernik]

This is what I found.

S.cerevisiae builds it's own microclimate barrier (krausen) to protect itself from a free oxygen surface to keep competing yeasts out.

There is also this. Scroll down to film yeasts.

 

[dantheman13]

This is what I found.

S.cerevisiae builds it's own microclimate barrier (krausen) to protect itself from a free oxygen surface to keep competing yeasts out.

There is also this. Scroll down to film yeasts.

Thanks! From the second link: "Yeasts are divided into two groups on the basis of the type of growth in or on liquid media. So-called film yeasts, or oxidative yeasts, grow as a film or scum on the surface, while the others, the fermentative yeasts, grow throughout the liquid."

That is helpful, thank you.