Graduate Thesis Or Dissertation
 

Pinot noir Sensory Impacts of Malolactic Bacteria During Concurrent Malolactic Fermentation and Use of Torulaspora delbrueckii During Cold Soak

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  • Malolactic fermentation (MLF) is a key process in red wine production. It is traditionally conducted following alcoholic fermentation but can sometimes result in lengthy overall fermentation times and delayed addition of sulfur dioxide to stabilize the wine. MLF can instead be conducted concurrently with alcoholic fermentation to shorten fermentation length, confer microbial stability, and allow starter bacteria to acclimate to higher alcohol wines. However, concurrent MLF is not commonly used in red winemaking due to concerns about color loss, microbial antagonism, and negative sensory impacts. Heterofermentative bacteria like Oenococcus oeni can produce spoilage compounds like acetic acid and can consume acetaldehyde, a key compound in color stability. This work investigates the use of a homofermentative bacteria, Lactobacillus plantarum as a possible method for mitigating the potential negative effects of concurrent malolactic fermentation. This work also investigated the influence of MLF timing on Pinot noir wine color and sensory properties using O. oeni and L. plantarum. The addition of a non-Saccharomyces yeast, T. delbrueckii, during cold soak was also studied due to potential interactions with malolactic bacteria and production of acetaldehyde. Pinot noir wines were produced with and without cold soaking, with and without T. delbrueckii, and with a concurrent or sequential MLF using either O. oeni or L. plantarum. Cold soaking with T. delbrueckii yielded higher acetaldehyde concentrations at the end of cold soak and during alcoholic fermentation but did not result in significant color differences at the end of MLF. Concurrent MLFs initially decreased color density and polymeric pigment content but only if a cold soak had also been undertaken. However, after nine months of aging, differences in wine color and polymeric pigment content noted were no longer present. The wines produced with L. plantarum contained more polymeric pigment following concurrent fermentations when a cold soak was used compared to the O. oeni counterparts. Wines were assessed by a sensory panel using hedonic and rate all that apply analyses to determine liking, aroma, and mouthfeel characteristics. Wines produced without a cold soak had significantly different aroma than those produced with a cold soak. Concurrent MLF wines had significantly different aromas than sequential MLF wines, and for both aroma and mouthfeel, an interaction was found between cold soaking and MLF timing. When not paired with cold soak, concurrent MLF wines were described as having woody and spiced aromas, while sequential MLF wines were described as having fruity and herbal aromas. Use of T. delbrueckii during cold soaking resulted in wines described as having a softer mouthfeel than their counterparts. This work demonstrates that many of the concerns associated with the use of concurrent MLF were either not found in Pinot noir or, in the case of color reduction, may be remedied by a short aging step. Further research is necessary to elucidate the mechanism responsible for the interaction between cold soaking and MLF timing and to define other key nuances in the use of concurrent MLFs.
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Déclaration de droits
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  • Funding provided by the Oregon Wine Board and the American Vineyard Foundation.
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