Impact of malolactic fermentation timing and the use of non-Saccharomyces yeast during cold soaking on Pinot noir wine color and sensory properties. (2024-2704

The malolactic fermentation (MLF) is a key process in the production of red wines and some white wines.  While it is commonly conducted after the completion of the alcoholic fermentation (sequential), it can also be induced at the same time where Oenococcus oeni is inoculated shortly after the beginning of alcoholic fermentation (AF).  While a concurrent MLF is typically completed in a shorter time period than a sequential MLF, it is often avoided due to concerns over the production of excess acetic acid, loss of color, and competition with the fermentative yeast Saccharomyces cerevisiae.  Finally, the impact of concurrent MLF on the organoleptic qualities of red wines is relatively unknown and may present an obstacle for the adoption of this practice.  This project addressed some of these concerns and determined the impact of MLF timing on Pinot noir wine chemical and sensory properties.  In addition, the use of non- Saccharomyces yeast during cold soaking and the potential impact on a concurrent MLF was determined.

The timing of MLF inoculation had a significant impact on color with wines produced using a concurrent MLF having lower color density and polymeric pigments.  Interestingly, lower color and polymeric pigment content was only present in concurrent wines that had undergone a cold soak.  While MLF timing affected color, the addition of Torulaspora delbrueckii during cold soaking did not.  For the sequential MLF treatments, there was no difference in color or polymeric pigment content in wines that underwent a cold soak compared to those that did not.  After nine months of aging, the color and polymeric pigment differences present at the end of MLF were no longer present.  Of note was that wines produced with a concurrent MLF increased in color while all other wines saw a reduction in color as is typical during aging.  In addition, all wines increased significantly in their polymeric pigment content.  While all treatments increased in polymeric pigments, the largest increases in polymeric pigment occurred for the three treatments that underwent concurrent MLF.

While measurable color differences in the wines declined during aging, sensory analysis did reveal color differences between some treatments.  Wine produced with a concurrent MLF was noted to be more violet in color than other wines while wine produced with cold soaking + T.delbrueckii + concurrent MLF had higher red intensity.  The more red colored wine was also liked significantly more than the other wines when evaluated in clear glasses.  However, there were no differences in liking when black glasses were used emphasizing the effect of color on liking.  Sensory evaluation also revealed significant differences between the wines in aroma and mouthfeel.  Wines produced without cold soaking had significantly different aroma than those produced with a cold soak, and non-cold soak wines were also significantly different from each other due to MLF timing.  In contrast, timing of MLF did not impact the aroma of the cold soaked wines, whether an addition of T. delbrueckii had been made or not.  Non-cold soaked wines made with a sequential MLF were described as having cedar, fruity, and herbal aromas while those made with a concurrent MLF were described as having spicy, dried fruit, and woody aromas.

Cold soaked wines made with a sequential MLF had dark berry fruit and leather aromas.  For mouthfeel, the major differences were between wines that had T. delbrueckii added and those that did not.  Cold soaked wines with an addition of T. delbrueckii produced wines with desirable mouthfeel characteristics such as smooth, soft, and balanced.

Wines produced in 2023 included an additional variable, the use of Lactiplantibacillus plantarum to conduct MLF.  As was seen with the 2022 wines, the use of T. delbrueckii and/or conducting concurrent MLF had minimal impact on the speed of the alcoholic fermentation.  MLFs conducted by L. plantarum proceeded rapidly due to the higher inoculation rate but those conducted by O. oeni also completed MLF in 14 days or less.  Early analysis of color and phenolic properties shows different color trends between wines produced with concurrent MLFs induced by O. oeni or L. plantarum.  Polymeric pigments  trended higher  in concurrent MLFs with L. plantarum compared to O. oeni, except for concurrent MLF wines with an addition of T. delbrueckii (no cold soak).  Further analysis of these wines will determine which variables are significant as well as any significant interactions between the treatments.