Erick Casalta

Diversity and dynamics of the microbial community during the manufacture of Calenzana, an artisanal Corsican cheese

We studied the diversity and dynamics of the microbiota of Calenzana, a Corsican raw milk cheese by microbial counting and culture-independent methods (TTGE and DGGE). Cheese from two farms, one producing goat cheese and the other one sheep cheese, was studied. The usual process for cheese making, without starter adjunct, was used. Lactococci and mesophilic lactobacilli were the dominant components of the flora during the early stages of the process. Microbial counting showed that the populations of salt-tolerant bacteria, yeasts and moulds were lower than in other artisanal Corsican cheeses. This difference was probably due to the surface microflora being removed during ripening. TTGE indicated that Lactococcus lactis ssp. lactis was the dominant subspecies throughout the process of Calenzana cheese making. DGGE showed the presence of numerous surface bacteria, (coryneforms) and various Gram-negative bacteria. Relationships between physico-chemical characteristics of the cheese and microflora change were also established. For example, the high NaCl content may explain the decrease of the lactic acid bacterial population during ripening. This study shows the consequences of various technological parameters on the diversity and dynamics of dairy microbial community.

A comparison of laboratory and pilot-scale fermentations in winemaking conditions

We investigated the influence of the fermenter size on alcoholic fermentation. Experiments were carried out at pilot scale, in 100-L fermenters, and at laboratory scale, in stirred and static 1-L fermenters. Two musts, Grenache blanc and Sauvignon, were fermented with and without the addition of solid particles from grape musts. Highly clarified must fermentation kinetics was strongly affected by the scale of the experiment, with slower fermentation occurring in the 100-L fermenter. Alcohol, ester, and thiol synthesis in clarified sauvignon must fermentation was also strongly correlated with the fermentation scale. Addition of solid particles from grape tended to reduce the effects on kinetics associated with increasing the scale of the fermentation, by increasing the maximum rate of CO2 production, and by shortening the duration of fermentation. The addition of such particles also decreased the effects of scaling up the fermentation on the concentration of some volatile compounds, i.e., isoamyl acetate, ethyl octanoate, but did not decrease this effect for other compounds, such as isobutyl acetate, isobutanol, and 3-mercaptohexanol.

Review: Characterization and Role of Grape Solids during Alcoholic Fermentation under Enological Conditions

During wine production, grape solids have a large impact on the fermentation characteristics and organoleptic qualities of the resulting wine. Here we review the research on grape solids. We begin by focusing on the origin, physical characteristics, and composition of these solids and on the changes in these factors that occur during fermentation. We then consider the impact of solids on fermentation, the role of sterols, the control of solids, and interactions between solids and other nutrients. Solids exert their effects on alcoholic fermentation mainly by modulating lipid supply. The balance between solids content and nitrogen is a key factor in fermentation control. The study of grape solids is in its infancy and requires further development. Knowledge of the composition of these solids and of sterol uptake mechanisms by yeast should facilitate improvements in fermentation control.