Posts

Showing posts from August, 2019

Utilisation of nitrogenous compounds by commercial non-Saccharomyces yeasts

Image
By Karien O'Kennedy
The study investigated the preferences and order of uptake of nitrogen sources for various commercially available non-Saccharomyces yeasts. The influence on growth and fermentation kinetics, as well as aroma formation, was also investigated.
Project layout:
Five commercial yeasts were used in the study: EC 1118 - Saccharomyces cerevisiae (Lallemand)Viniflora Frootzen - Pichia kluyveri (Chr. Hansen)Biodiva TD291 – Torulaspora delbrueckii (Lallemand)Flavia MP346 – Metschnikowia pulcherrima (Lallemand)Viniflora Concerto – Lachancea thermotolerance (Chr. Hansen)
Fermentations were performed in three different synthetic grape musts with a total YAN of 200 mg/l. Treatment 1 – Amino acids in equal amounts of assimilable nitrogen levels plus ammoniumTreatment 2 - Amino acids in equal amounts of assimilable nitrogen levels without ammoniumTreatment 3 – grape must-like nitrogen concentrations
Pure culture fermentations of all five yeasts were conducted as well as co-inoc…

Nitrogen additions can kill your yeast

Image
Aim: Nitrogen availability is an essential parameter for wine alcoholic fermentation. Moreover, recent results have shown that it plays a key role in yeast cell death in interaction with micronutrients limitations such as lipids or vitamins. Previously researchers have found that yeast cell death was triggered by starvation for a set of micronutrients, including oleic acid, ergosterol, pantothenic acid and nicotinic acid whenever the level of nitrogen was high, but not in low nitrogen conditions. In this study researchers examined the impact of the nature of the nitrogen source in the light of these previous results.
Methods and results: 19 Amino acids or NH4+ were added, in amounts corresponding to 354 mg/L assimilable nitrogen, to an oenological medium that was low in nitrogen and oleic acid.Yeast viability in function of the fermentation progress was assessed and showed differences in cell death during the alcoholic fermentation in function of the amino acid added.The addition of NH4…

Sensory attributes of wines made from vines of differing phosphorus status

Image
Aim: The implications of water and nutrient deficiencies for photosynthesis, dry matter production, and yield have been well documented. However, whereas multiple studies show that water deficits affect grape and wine quality as well as wine sensory characteristics, the corresponding implications of manipulating vine nutrient status through fertilizer additions remain largely unexplored.
Methods and results:  In this study, phosphorus (P) fertilizers were applied to P-deficient vineyards of Cabernet Sauvignon, Chardonnay, and Chenin blanc growing in rhyolite, granite, and schist derived soils. Bloomtime leaf lamina P levels, basic soil chemical characteristics, juice P, and wine chemical parameters were measured after harvest. A highly sensitive protocol for sensory evaluation was used to test the wines made from the treated and untreated grapes for differences in wine appearance, flavor, aroma, and taste. All P additions were effective in rapidly increasing both vine P status and P in t…

Influence of vertical training systems on warm climate red winemaking

Image
Aim: A study was performed on the influence three vertical training systems had on wine composition in warm climates, analysing the wine’s polyphenol and volatile compound contents and sensory properties.
Methods and results: 
The polyphenols and volatile compound content of wines was analysed together with their sensory properties.The effect of different training systems (double Guyot (CT), Smart-Dyson variation (SM), and Triple cordon (TC)) was studied in Tempranillo (TEMP), Syrah (SYR) and Tintilla de Rota (TR) cultivars to determine their influence on red winemaking over a two-year period.Statistical analysis was conducted with Cultivar and Year as factors.TC delayed grape ripening and reduced the alcohol in the wine when grapes from the three training systems were picked on the same date.Overall, no differences were found in polyphenol content.Higher alcohol acetates, ethyl esters of branched acids and various esters were found to be influenced, and some of these compounds are relate…