Temperature-Dependent Kinetic Model for Nitrogen-Limited Wine Fermentations

Abstract

A physical and mathematical model for wine fermentation kinetics was adapted to include the influence of temperature, perhaps the most critical factor influencing fermentation kinetics. The model was based on flask-scale white wine fermentations at different temperatures (11 to 35°C) and different initial concentrations of sugar (265 to 300 g/liter) and nitrogen (70 to 350 mg N/liter). The results show that fermentation temperature and inadequate levels of nitrogen will cause stuck or sluggish fermentations. Model parameters representing cell growth rate, sugar utilization rate, and the inactivation rate of cells in the presence of ethanol are highly temperature dependent. All other variables (yield coefficient of cell mass to utilized nitrogen, yield coefficient of ethanol to utilized sugar, Monod constant for nitrogen-limited growth, and Michaelis-Mententype constant for sugar transport) were determined to vary insignificantly with temperature. The resulting mathematical model accurately predicts the observed wine fermentation kinetics with respect to different temperatures and different initial conditions, including data from fermentations not used for model development. This is the first wine fermentation model that accurately predicts a transition from sluggish to normal to stuck fermentations as temperature increases from 11 to 35°C. Furthermore, this comprehensive model provides insight into combined effects of time, temperature, and ethanol concentration on yeast (Saccharomyces cerevisiae) activity and physiology.The progress of a wine fermentation is determined by the concentration of residual sugar. Problem fermentations occur when the completion of sugar utilization exceeds 7 to 10 days (sluggish fermentations) or when sugar utilization ceases with more than 0.4% wt/vol residual sugar still present in the wine (stuck fermentations) (5). Sluggish and stuck wine fermentations are often associated with musts that contain inadequate nutrients. The primary nutrient associated with these problem fermentations is nitrogen. The minimum concentration of required nitrogen in order to complete fermentation may be dependent upon other factors, such as temperature and initial sugar concentration. More comprehensive reviews of all known factors that lead to problem fermentations are available (1,5,6,14); however, in this work, to predict problem fermentations, we concentrated on developing a comprehensive model that includes the three main factors of temperature and initial nitrogen and sugar concentrations.These three variables are well-known critical factors for determining the kinetics of wine fermentations. Ough and Amerine performed extensive studies to characterize the effects of temperature on cell growth, sugar utilization, and ethanol production (25,26). Others have studied yeast (Saccharomyces cerevisiae) sensitivity to ethanol at various temperatures (22,27,28). In addition, insufficient nitrogen has been well documented as an important factor that leads to stuck and sluggish fermentations (1,2,5,14,15,2...

Examining the Role of Membrane Lipid Composition in Determining the Ethanol Tolerance of Saccharomyces cerevisiae

“…Once the available nitrogen has been depleted, the yeast cells begin to transition into stationary-phase metabolism, where the yeast cell population achieves its highest density. During early stationaryphase metabolism, significant amounts of sugar are converted to ethanol and cell viability remains relatively high, though fermentation begins to slow (5)(6)(7). As the sugar concentration continues to fall (and ethanol levels rise), the viable yeast cell population does not change significantly until virtually all of the sugar has been utilized, and the yeast cells then begin to die.…”

“…In the first time period, known as the latent or lag phase, yeast cells are utilizing sugar and other nutrients, particularly nitrogen, for energy and to initiate cell growth; however, they are also adapting to the new environmental stresses and conditions (5). Upon adaptation, the yeast enters the exponential growth phase, where it begins to grow at a high rate that is primarily limited by the concentration of nitrogen (6)(7)(8). During this same growth period, dissolved oxygen in the fermentation medium is utilized by yeast to produce ergosterol, the major sterol in yeast, and unsaturated fatty acids that will be incorporated into diacylglycerol (DAG), the precursor to all of the phospholipids that compose the yeast cell membrane (5).…”

Reconciling Competing Models: A Case Study of Wine Fermentation Kinetics

“…The effect of these factors can directed computed by using devices to measure the number of cells (by using Hemacytometer or Neubauer for example) on fermentation samples or by biotechnological tools as DNA Microarrays ( [14]) and PCR (Polymerase chain reaction, [13]). The estimations of profiles features as growth rate, death rate and yield coefficients developed in [6] can be extended to more strains and species. Microarrays and PCR can give us estimations of the profiles too.…”

“…It continues with a statistical step to evaluate the models, in function of experimental data ( [22], [15] and [16]). We defined discrete levels for each factor, for each configuration of factors and fermentation variable we statistically compared the results of three kinetic fermentation models ( [6], [22] and [26]) with the experimental results and we obtained quality indexes of each model (Figure 2). We finished with the construction of a combined model, where one selects the best resolution method for each fermentation variable and configuration of factors (Table 4).…”

“…The Coleman model ( [6]) was built on the model previously presented by [7] to include the effects of temperature. Its main goal is introducing temperature dependency to predict difficult fermentations.…”