On Mar 23, 1:00 pm, "Paul E. Lehmann" > wrote:
>
> > Jim
>
> In my opinion, the yeast does not contribute
> directly to the flavours. Each strain has its
> temperature range, pH range and acidity that it
> will perform best and thus possibly allow
> flavours ALREADY PRESENT IN THE FRUIT to come out
> or be suppressed. This is my personal opinion
> and I am sure there are those who will disagree
> with me.
>
> I have never done the following but I think it
> would lend some insight:
>
> Make a water sugar solution to about 22 brix and
> bring it up to a pH of say 3.5 - no fruit or
> flavouring and ferment with different yeast. My
> bet is that you will not get that "Blackberry",
> "Plum" or whatever descriptor you choose to use.
> I know that the yeast manufactures make all kinds
> of claims that their yeast will add such and such
> flaovours but I ain't buying it.
>
> Some have claimed to use different yeast on a
> divided lot of the same fruit and fermented and
> could tell a difference. Again, there may be a
> difference but I doubt the Yeast produced the
> flavours. Different strains merely allowed the
> flavours already present in the fruit to come
> out.
>
> Also, I have seen differences in the exact same
> fruit with divided lots in different fermentors
> or carboys and the exact same treatment and yeast
> used. This is just one of the mysteries of
> Organic Chemistry.
>

My understanding is they're not saying that the yeast produces all
those flavours and aromas on its own, rather that the yeast acts as a
catalyst that emphasizes certain characteristics. In that view it's
not black or white, i.e, the environmental characteristics like pH,
temperature, etc. of course contribute to how the yeast performs but
that doesn't preclude the yeast from making its imprint on the must.

I'm not very good in picking up subtle differences between batches
done with different yeasts, but I've had one very clear case where the
result went along the lines of what the yeast company said - we used
D21 and D254 on Petite Sirah and the D21 batch had noticeably more
acidity in the end, not by measurement but on the palate. This was
still obvious after 1 year of aging.

Over the years, I've come up with some yeast favourites for different
wine styles, and the selections were originally based mostly on the
purported style effects of the yeast, with the environmental factors
like temperature range just as a rough preselection step. So even if
some or most of the marketing blurbs were just hype, I'm happy with
the practical results.

Pp