Need a basic understanding about yeast

I have zero knowledge about the subject and was hoping someone could fill me in on the basics. I have heard of a few types of yeast used (red star, lalvin, pasteur… natural). What are the differences and how would the end result be any different? Also would a organic vineyard/winery have to use natural yeast? If so why and what difference may there be compared to commercial yeast [cheers.gif]

Try this: http://morewinemaking.com/public/pdf/wyeastpair.pdf

Thanks Rama. Good info to start.

Ed,

The UC Davis professors will say and have said that designer yeasts/packaged yeasts do not significantly affect the ending bottled wine with regards to taste characteristics past the short term. One of the things I remembered from my Davis intro to winemaking extension course I took.
Maybe there has been some newer research that disproves this?

What is different is that various yeasts will have different operating environment characteristics. So if your primary ferment tank is getting a bit too alcoholic, for whatever reason, and it’s stalling you can innoculate with a strain of yeast that can survive in 15-18% ethanol to start the fermentation again.

Of course there are many winemakers and consumers who disagree.

Yes, just short term.

Yeast eat sugar and poop out alcohol. Yes, it is more complex than that (a bit), but that is the most important thing to know. Before I went to school I thought it was all very mysterious, and I wanted to know everything there was to know about yeast, but really, the eating and pooping thing is what it comes down to.
Yeast like sugar, but not too much. They like oxygen. They like a nice warm temp, just like humans. It’s really not terribly complex.

I’m a novice winemaker, but an experienced beer brewer. In beer, different yeast strains do make a substantial difference. Yes, most beers are consumed in the “short term”.

However different yeasts are more prone to producing diacetyl, phenols, DMS, etc at different temperature ranges. I don’t think most of these “blow off” with age. So while you may end up with the same long term product via different yeasts under different controlled environments, if the environment can’t be completely controlled, it seems you should bias towards a yeast that behaves favorably in those conditions. So yeast selection could be important.

I was speaking more mechanistically. Yes, yeast can have impacts such as short term flavor/aroma differences, ethanol tolerance, etc., but I think a lot of the claims made by the yeast companies as to the characteristics their yeasts impart are WAY overstated. I personally think grape quality and winemaking techniques will trump yeast differences for the most part, and any differences noticed in a very young wine (Beaujolais Nouveau, early drinking whites) will disappear at the one year mark and later. Especially in heavier reds, these differences will be negligible.
There are some yeasts that have been genetically modified to produce more aroma compounds, etc., but as far as I know, they are not being approved by governments for the same reasons many GMO’s are not, with the hurdles they face possibly being insurmountable. Yeasts bred in the traditional ways have moderate impact at best, IMO.

One of the major differences with yeast is that some ferment slowly at cool temperatures while others might not be able to take the cool temps. This has a definite effect on the outcome of a wine, especially regarding fruitiness. Some yeasts ferment quickly; some do not, and a lot of that difference may be based on the nutrition of the must. Length of time fermenting generally has an effect on the outcome.

There is no simple answer except that. like Linda says, yeast eat sugar…

An article on manipulating the taste of wine by choosing specific yeasts:

The most important difference between yeasts is the alcohol tolerance. I’ve you’ve got a high brix fruit and you use a yeast that doesn’t have the capacity to ferment the wine you could end up with a stuck fermentation that’s really hard to restart.

Aside from alcohol tolerance the yeast strains do offer different flavor and aroma profiles. I once made a Riesling and fermented half with one yeast and half with another strain. I took the two finished wines and blended them in varying proportions. We had some non-wine-geek friends over for a tasting and they each could discern a difference from wine to wine. We all had different favorites too.

The Yeast and Grape Pairing Guide that Rama shared is well worth a read.