The Rise and Fall of Yeast and Bacteria During Fermentation: Part 1

Recently, our friend, the vineyard manager and erstwhile winemaker was lamenting that his wine was stinky. I immediately thought of laccase as his problem, but then I might have been a little premature.
I'm reading Wine Microbiology written by Kenneth C. Fugelsang and Charles G. Edwards. In this book, Fugelsang and Edwards mention that in the case of sound, undamaged grapes, the viable population of yeasts ranges from 10³ to 10⁵ CFU(colony forming units)/mL.

The most common yeast on clean grapes is Kloeckera apiculata which can account for more than 50% of the total yeast recovered from fruit. In addition, clean fruit can also contain Candida, Cryptococcus, Debaryomyces, Hansenula, Issatchenkia, Kluyveromyces, Metschnikovia, Pichia, and Rhodotorula. Contrast that to the wine yeast Saccharomyces, which occurs naturally on the grape at 50 CFU/ml, several orders of magnitude less than K. apiculata. So, the question is, why doesn't K. apiculata dominate the fermentation?
Although K. apiculata and it's cohorts may be the dominant yeasts that come in with clean fruit, the winemaker may choose to inoculate the must with a cultured yeast, thereby insuring that the fermentation begins with some kind of Saccharomyces. However, if a "natural" fermentation is the goal, then the start of the fermentation will be dominated by K. apiculata and some winemakers say that this adds to the complexity of the resultant wine. If natural fermentation is used, the following graph shows the rise and fall of the various yeasts and bacteria that will dominate the different phases of wine development.

(A) K. apiculata may be present in large numbers during pre-fermentation and low fermentation temperatures (10-15^oC/50-59^oF) can extend the survival of non-Saccharomyces yeasts during the early stages of fermentation. The presence of K. apiculata during fermentation can be problematical because they can make prodigious amounts of ethyl acetate and amyl acetate, and is quite efficient in quickly depleting nutrients, particularly thiamine and other vitamins. They can also form a thick, slimy scum or stringy clumps that can later fall out as fluffy lees.² But once fermentation has begun and alcohol concentrations have reached 5-6%, alcohol tolerant yeasts, such as Saccharomyces can become the dominant species.
(B)The rise of Saccharomyces species should occur within one day of the start of fermentation. During primary fermentation, Saccharomyces becomes the dominant species because Darwinian law of survival of the fittest applies in this system. Here, I have been blogging about vinification with very clean starting material (grapes) but my next blog will be about making wine with less that pristine grapes, or explaining what happens during the rise and fall of yeast and bacteria during secondary fermentation and wine conservation and aging ((C) and (D)).
References:
1. Kenneth C. Fugelsang and Charles G. Edwards, Wine Microbiology, Springer Science and Business Media, LLC, 2007.
2. Lisa van de Water, Monitoring Microbes During Fermentation, Practical Winery & Vineyard Journal, September/October 2009.