Model z2

During fermentation, the cell population was determined using a Coulter counter (Model Z2, Beckman-Coulter, Margency, France) fitted with a 100 μm aperture probe.

All fermentations were carried out in synthetic musts simulating a standard grape juice (Bely et al., 1990 (link)). The detailed compositions of the different stock solutions used for the preparation of this synthetic medium are identical to those presented in Mouret et al. (2014b) (link). All musts contained 200 g/L of sugars (100 g/L glucose and 100 g/L fructose) and their pH was 3.3. Three initial assimilable nitrogen (composed of ammonium chloride and a mixture of amino acids) concentrations were tested: 70, 140, and 210 mgN/L, respectively, corresponding to media SM70, SM140, and SM210. The proportions of the different sources were identical in all three media.
Fermentations in SM70, SM140, and SM210 were run in 10-liter stainless steel tanks, at 18, 23, and 28°C. The amount of CO₂ released was accurately and automatically measured with a gas mass flowmeter, for calculation of the rate of CO₂ production (dCO₂/dt).
Different concentrations—50, 100, and 150 mg N/L—of mineral nitrogen (di-ammonium phosphate) were added at 20 g/L of produced CO₂ (corresponding to 24% of fermentation progress). Nitrogen additions were performed automatically using a peristaltic pump fed with the nitrogen solution. During fermentation, the total cell population was determined using a Beckman Coulter counter (Model Z2, Beckman-Coulter, Margency, France) fitted with a 100 μm aperture probe.

During fermentation, the total cell population was determined using a Beckman Coulter counter (Model Z2, Beckman-Coulter, Margency, France) fitted with a 100 μm aperture probe.