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September 2015 P R A C T I C A L W I N E R Y & V I N E YA R D 61 W I N E M A K I N G Quality made in Germany 29.07.15 09:28 35, 50, 75, 100 and 150 mg/L SO 2 , as well as 0 and 50 mg/L SO 2 inoculated with commer- cial Saccharomyces cerevisiae EC-1118. The fermentations were conducted rather con- ventionally and sampled after one, two, three, five, seven, 10, 14 and 21 days. That is 11 treatments, in triplicate, at eight sampling times, for a total of 264 unique samples. Simply put, no other current method would allow for such rapid and in-depth analysis of so many treatments/time points as was possible here with marker gene sequencing. What did all this sequencing reveal? For one, SO 2 mainly impacted bacterial diversity, as fungal populations across the range of sulfite additions did not appear to differ significantly from one another throughout the course of the fermenta- tions. This lack of significant differences may have been partly due to high variation within replicate fermenta- tions. Bacterial diversity, on the other hand, was found to be significantly impacted by different doses of SO 2 . For uninoculated fermen- tations, 25 mg/L or more of SO 2 seemed to stabilize bac- terial populations. When SO 2 was less than 25 mg/L, however, bacterial popula- tions shifted in ways that were somewhat surprising. In no-sulfite-added musts, the average number of bacte- rial species decreased rapidly after 10 days and remained lower than the sulfited musts. This was likely caused by the growth of a few species, especially those in the genus Lactobacillus and the larger family, Lactobacillaceae, which dominated the bacterial com- munities and caused the less- abundant taxa to fall below detectable levels. In the low-sulfite musts (15 and 20 mg/L) there were sig- nificant increases in the pop- ulations of acetic acid bacteria of the genus Gluconobacter that were not observed else- where. These low- and no- sulfite musts were also slower to begin active fermentation and had higher Brix values (2.2º, 0.6º and -0.3º Brix) after 21 days than the greater than 25 mg/L sulfite treatments (-1.0º to -1.5º Brix). This sug- gests that the growth of these bacteria may have impacted fermentation completion or, conversely, the conditions that restricted fermentation led to their population increases. Impact of yeast inoculation on bacterial populations A stabilizing effect similar to adding more than 25 mg/L SO 2 was achieved by inocula- tion with a strong S. cerevisiae starter culture, even with zero SO 2 added. Fermentation also proceeded more rapidly and to a slightly greater degree of completion when inoculated with yeast. Thus, inoculation alone may provide a reason- able level of protection and contribute to microbial sta- bility during fermentation of non-sulfited wines. Emphasis should be placed on the fact that this observation applies to the period of active fermen- tation, and such a protective effect may not persist into later stages of winemaking. Some additional results of the study, the significance of which might be less obvious to most winemakers, include the abundant presence of the bacterial genus Erwinia and other members of the same Enterorbacteriaceae family, regardless of sulfite levels. Traditionally, these bacteria have not been considered to be participatory members of wine fermentation, as they have not been isolated from wine by culture-based methods. The high relative abun- dance of Erwinia from the very beginning of fermen- tation supports the thought that they are environmen- tal microbes, coming from the surface of the grapes at pressing, and are not neces- sarily active during the fer- mentation. Their apparent persisting presence through