Issue link: http://winesandvines.uberflip.com/i/658375
April 2016 WINES&VINES 85 WINE EAST WINEMAKING Why the long fermentation? Spontaneous fermentations have been observed to drag on for weeks or months longer than com- parable inoculated juices, either getting off to a sluggish start or hanging on to the last few grams of residual sugar. A long lag phase (the period before fermentation takes off) can result from low ini- tial YAN, nitrogen depletion by non-Saccharomyces yeasts (as dis- cussed above) or a low initial yeast biomass (compared to that added in a commercial inocula- tion), compounded by the usual impacts of sub-optimal environ- mental parameters like tempera- ture, pH, etc. Toxins released by "killer" yeast and some non-Sac- charomyces strains also can inhibit fermentation progression. Notably, a 2014 study by Jarosz et al. identified an inheritable met- abolic change induced in yeast by common wine bacteria that allows affected yeast to metabolize non- glucose carbon sources and reduce ethanol production. This change is mutually beneficial to yeast and bacteria, prolonging their co-exis- tence in fermentation media, but results in stuck or sluggish fermen- tation problematic to winemakers. The particulars of this metabolic shift are still under investigation, and its impact on nitrogen con- sumption is unknown. A New York case study In the New York Finger Lakes, YAN concentrations (especially in Ries- ling) are usually lower than the 140 mg of nitrogen per liter (N/L) considered the bare minimum for successful fermentation. As the popularity of spontaneously fer- mented Riesling has grown in re- cent years, the Cornell Enology Extension Lab conducted an initial assessment of YAN requirements and microflora in five spontaneous fermentations at two commercial Finger Lakes wineries during the 2014-15 season. To assess micro- bial populations before fermenta- tion, grape samples were collected from each vineyard before harvest, and the surface of winery equip- ment was sampled using sterile cotton swabs. Once grapes were received and crushed, researchers monitored fermentation kinetics, YAN consumption and microbial populations in an effort to under- stand the interaction of microflora and nitrogen requirements. As expected, fermentation times for all Rieslings were con- siderably longer than inoculated fermentations, though kinetics differed by winery. Winery 1's fer- mentations started quickly, then slowed considerably and were ultimately stopped by the wine- maker around 90 days post-inoc- ulation. In contrast, Winery 2's fermentations had very long lag phases, but once fermentation started, sugars were consumed at a steady rate. Differences in kinet- ics may be partially explained by different juice YAN concentrations or different microbial populations, so these factors were examined in greater detail. Initial YAN concentrations were low in four of the five juices (rang- ing from 68-144 mg N/L), only surpassing the standard recom- mended level of 200 mg N/L in one juice (231 mg N/L). As in inocu- lated fermentations, inorganic ni- trogen was consumed faster than organic nitrogen, and ammonium was exhausted from all fermenta- tions except the one with the high- est YAN. In contrast, primary amino nitrogen (PAN) concentra- tion never reached zero; in fact, a slight increase in PAN was ob- served in the final stages of all fermentations. Notably, YAN con- sumption (calculated as [initial YAN]-[final YAN]) in all fermenta- tions was at or below 140 mg/L. One factor that may contrib- ute to this seemingly small nitro- gen demand is residual sugar (RS) concentration. In studies that measure nitrogen require- ments, RS in successful fermenta- tions is usually less than 1 g/L, while the wines monitored in this study retained an average 8.6 and 23.5 g/L RS (in Wineries 1 and 2, respectively) for stylistic rea- s o n s . A n o t h e r, a s d i s c u s s e d above, is the release of PAN fol- lowing the death of non-Saccha- romyces yeast in mid- and late fermentation. As this activity is hard to measure accurately, it complicates robust assessment of total YAN consumption. The winery-specific fermenta- tion profiles are partially explained - B E C O PA D - Y E A S T & E N Z Y M E S - C R U S H PA D E Q U I P M E N T - S T E R I L E F I LT R AT I O N - W I N E R Y H O S E - O A K A LT E R N AT I V E S EASTERN WINE LABS Serving the Analytical needs of East Coast Wineries WWW.EASTERNWINELABS.COM Ph 609-859-4302 Cell 609-668-2854 chemist@easternwinelabs.com AOAC Member EasternWineLab_Mar09.qxp 1/22/09 9:47 AM Page 1