A Review of Sensors for the Monitoring, Modeling, and Control of Commercial Wine Fermentations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors reviewed sensors for the monitoring, modeling and control of commercial wine fermentations. The topic is interesting. The manuscript is generally organized well and well written. I would like to recommend it for publication after revisions. The detailed comments are as follows:

1. Keywords, replace wine fermentation with synonyms or alternative expressions.
2. Introduction, are there other reviews already published in this specific area?
3. The references were not appropriate. In Introduction, only three references? No references from Line 77-96, 116-155…
4. Source of the data in Figures and Tables should be cited.
5. Check the reference styles. For example, Line 1214, no page numbers. Line 1265 1-1?

Author Response

1. Keywords, replace wine fermentation with synonyms or alternative expressions.

Thank you for your comment. Based on the topic of this paper, we believe “wine fermentation” is an important keyword for others to find this review paper in the future.

2. Introduction, are there other reviews already published in this specific area?

3. The references were not appropriate. In Introduction, only three references? No references from Line 77-96, 116-155…

We conducted a thorough literature search and found that comprehensive reviews specifically addressing this topic are indeed limited. While there are scattered studies that touch on related aspects, none of which provide the systematic overview presented here. This scarcity of dedicated review literature underscores the need for our work and reinforces its potential contribution to advancing understanding in this field. We have included all relevant reviews we could identify in our reference list.

 

4. Source of the data in Figures and Tables should be cited.

Thank you for your comment. Citations for figures and tables have been added where applicable.

5. Check the reference styles. For example, Line 1214, no page numbers. Line 1265 1-1?

The references have been reviewed and corrections made where necessary.

Reviewer 2 Report

Comments and Suggestions for Authors

     The article ‘A Review of Sensors for the Monitoring, Modeling and Control of Commercial Wine Fermentations‘.

     Thank you for the opportunity to review this paper. I read it with interest. This manuscript reviews sensors, particularly online sensors, used in commercial winemaking. Measurements of solution parameters (including density, mass, volume, osmotic pressure), sugar consumption, ethanol and glycerol production, redox potential, mass and cell viability during fermentation are discussed. Their significance in diagnostic and predictive models was analyzed. Methods were compared in terms of sensitivity, availability and suitability in large fermentations. Factors influencing the implementation of control strategies were also discussed and challenges and opportunities for further sensor development were presented.

     The work presents a good scientific level with visible elements of novelty. The title reflects its content. The individual parts constitute a compact and coherent study supported by relevant literature reports. The methods and means were sufficient to achieve the adopted goal. The analytical flow is correct. Both the Abstract and Conclusion sufficiently illustrate the content of the manuscript.

     The paper represents a good scientific level, and the research on topics presented in it can be useful in the future analysis of the subject. All analyses look good, however, I suggest you consider making the following adjustments:

1. Point 2. Wine Fermentation Characteristics - why the description omits the effect of containers on the fermentation process. Do the material and volume of the containers affect the fermentation process.
2. Figs. 1-4 - the figures shown are based on the authors' results or were taken from the literature.
3. Point 3.2 Temperature Gradients within Red Wine Fermentations - whether and what methods are used to clean the temperature sensors to ensure the best possible contact with the test medium.
4. Fig. 5 - it is suggested that the descriptions on the graph are enlarged to improve readability.
5. Line 376 - what percentage of the total height of the container is 1.4 m and 0.7 m in diameter.
6. Fig. 6 - whether these are in-house studies or drawings developed from literature.
7. Line 423 - the recirculation flow is internal as it can also be external outside the container.
8. Fig. 9 - it is suggested to enlarge the descriptions on the graph to improve readability. In addition, since a trend line is presented, the form of the fitting function should be given, together with the determination index. If the approximation is realized with an intercept at 0.0, the possible reasons for non-linearity in the lower measurement range should be described.
9. Figs. 10, 11, 12 and 13 - it is suggested to enlarge the descriptions in the graph to improve readability.
10. Point 12. Conclusions - consideration should be given to presenting some of the most important achievements of the study in the form of bullets. In the current form of this section, a long description causes the reader to get lost.
11. General: I) the figures presented in the study have no literature references. There is doubt as to whether they are authors' material or studies based on the literature; II) the study deals with sensors, but no schematics of even selected designs appear in the text.

Author Response

1. Point 2. Wine Fermentation Characteristics - why the description omits the effect of containers on the fermentation process. Do the material and volume of the containers affect the fermentation process.

Thank you for raising this important consideration. Our focus in this section is on the fundamental biochemical processes and kinetic parameters that govern fermentation across different systems. While container characteristics certainly affect practical implementation—particularly through thermal management, oxygen transfer rates, and sensor accessibility—these represent operational variables rather than changes to the core fermentation mechanisms we describe. Container effects primarily manifest through their influence on the temperature, mass transfer, and monitoring parameters we discuss elsewhere in the manuscript. We have clarified this scope in the revised text to better delineate between fundamental fermentation characteristics and operational considerations.

 

 

2. Figs. 1-4 - the figures shown are based on the authors' results or were taken from the literature.

Thank you for seeking clarification on the figure sources. Figures 1-4 are schematic representations that we developed based on well-established trends documented across multiple studies in the winemaking literature. While no single fermentation study has simultaneously measured all the parameters shown in these comprehensive figures, each individual trend depicted is supported by extensive research. These figures synthesize accepted knowledge to provide readers with a unified view of fermentation dynamics that would otherwise require consulting numerous separate sources. We have revised the figure captions to clearly indicate that these are schematic representations based on established literature trends, and we have added appropriate citations to support each depicted relationship.

3. Point 3.2 Temperature Gradients within Red Wine Fermentations - whether and what methods are used to clean the temperature sensors to ensure the best possible contact with the test medium.

Thank you for your comment. The cleaning and sanitation of the fermentor and any sensor in contact with juice or must is an important practical consideration. For the purposes of temperature sensors, however, the methods for cleaning are not relevant to the temperature gradients within red wine fermentation. We therefore chose to omit cleaning methods.

 

Our focus in this section is on the spatial and temporal characteristics of temperature gradients during fermentation rather than sensor maintenance protocols. The cleaning methods, while essential for data quality and food safety, do not influence the fundamental patterns of temperature distribution we describe. We acknowledge that sensor fouling could potentially affect measurement accuracy, but we assume that  established sanitation protocols are followed as per industry standards. We have added a brief note in the methods section acknowledging this assumption.

 

 

4. Fig. 5 - it is suggested that the descriptions on the graph are enlarged to improve readability.

Thank you for your comment. We have enlarged text in the graphs where possible.

5. Line 376 - what percentage of the total height of the container is 1.4 m and 0.7 m in diameter.

Based on the reference [17], the total height of the container is 1.59 meters, though the height of the container above the liquid level had no effect on study of thermal gradients and circulation patterns.

6. Fig. 6 - whether these are in-house studies or drawings developed from literature.

The drawings were done in-house and based on published literature (referenced in the section) and personal experience. The text has been updated for clarity.

7. Line 423 - the recirculation flow is internal as it can also be external outside the container.

In this section, we are specifically discussing natural convective recirculation that occurs within the fermentation vessel due to temperature and density gradients, as distinct from the forced external recirculation systems (using pumps and external loops) that we address in Figure 7 and the associated discussion. We have revised the sentence at line 423 to specify "internal natural convection" to clearly distinguish between these two types of recirculation and avoid confusion for readers.

8. Fig. 9 - it is suggested to enlarge the descriptions on the graph to improve readability. In addition, since a trend line is presented, the form of the fitting function should be given, together with the determination index. If the approximation is realized with an intercept at 0.0, the possible reasons for non-linearity in the lower measurement range should be described.

Thank you for your comment. We have increased text size in figures where possible. Figure 9 shows the difference in measured Brix between a hand-held densitometer and a Coriolis meter, therefore, there is no fitting function and the slope is 1.   

9. Figs. 10, 11, 12 and 13 - it is suggested to enlarge the descriptions in the graph to improve readability.

Thank you for your comment. We have increased text size in graphs where possible

10. Point 12. Conclusions - consideration should be given to presenting some of the most important achievements of the study in the form of bullets. In the current form of this section, a long description causes the reader to get lost.

Thank you for your comment. We have made significant rewrites to the conclusion to improve the readability, as shown below. We believe these changes significantly improve the manuscript.

“Wine fermentation monitoring faces a fundamental challenge: ensuring that sensor measurements accurately represent the entire fermentation volume. In unmixed fermentors, bubble-driven natural convection creates concentration gradients that vary with scale, fermentation rate, and geometry. These dynamics significantly impact sensor placement decisions and can cause fluctuating discrepancies between measured and actual fermentation conditions.

Our findings indicate that solution density monitoring using pressure transducers embedded in tank walls or vertical pump-over lines offers the most reliable commercial-scale method for parameter estimation within existing fermentation models. This approach enhances fermentation diagnosis and enables faster-than-real-time assessment of alternative control actions or interventions. By eliminating the need for manual sampling, it provides a robust foundation for regulating fermentation temperature and/or redox potential.

For red wine fermentations, separate control of the skin cap temperature is essential to limit volatile thiol formation due to low redox potentials while ensuring reproducible and quantitative phenolic extraction during pump-over and punch-down operations. Critical to this control is the comprehensive monitoring of skin cap temperature profiles—both vertically and radially—to enable continuous thermal management using cooler juice rather than relying on conventional twice-daily contacting practices.

A significant research gap exists in developing in-situ or in-line techniques for assessing yeast cell mass and viability within the complex matrix of grape pulp fragments, bacteria, and bubbles. Such measurements would enhance parameter estimation in fermentation models, particularly by monitoring viability decline during the non-growing phase and tracking growth dynamics during the growth phase. These measurements would provide crucial validation data regarding assimilable nitrogen availability and uptake, refining current mathematical models of wine fermentation. The persistent challenge of distinguishing between yeast and bacterial cells in mixed suspensions remains unresolved, yet quantifying cell growth is essential for advancing fermentation models, especially for malolactic fermentation.

Several offline techniques can be adapted for compact in-line applications, including cell mass, viability, and assimilable nitrogen concentration, which can facilitate comprehensive monitoring of yeast growth and parameter estimation related to substrate preference, nutrient uptake, and cell yield in wine fermentation models.  

Spectral methods, which are particularly well-suited for in-line applications, should be further developed to monitor the changes in phenolic components during red wine fermentations for information and/or control purposes.

Sensor systems for monitoring malolactic fermentation represent another promising direction, with controlled redox potential potentially enhancing secondary product formation and expediting completion. The ability to monitor cell growth during malolactic fermentation or detect undesirable bacterial populations alongside yeast cells would mark significant progress. These techniques merit further investigation to facilitate their implementation in both research and commercial fermentation settings.

As monitoring technology advances, the wine industry stands to benefit from more precise, data-driven fermentation management approaches that can enhance product consistency, quality, and innovation while reducing resource requirements and environmental impacts.”

11. General: I) the figures presented in the study have no literature references. There is doubt as to whether they are authors' material or studies based on the literature; II) the study deals with sensors, but no schematics of even selected designs appear in the text.

Thank you for your comment. We have updated the figure captions to clarify where the information comes from. We have also included a figure of a commercial redox potential sensor to enhance clarity when describing it in text.

Reviewer 3 Report

Comments and Suggestions for Authors

the article " A Review of Sensors for the Monitoring, Modeling and Control 

of Commercial Wine Fermentations"

 

The article has potential to be publish. However must do some corrections listed: 

 

1 - List of many models applied in this field. The literature shows many system of equation differential ordinary, regarding many modelos to specific growth;

2 - Input a list of value of parameters used to describe the kinetcs ; 

3 - Compare results in the literature obtained in wine fermentation ;
4 - In title contain the words "control", "modelling" and "control". Then, as the article is review article. I expected see many works related to it. 

 

Author Response

1 - List of many models applied in this field. The literature shows many system of equation differential ordinary, regarding many modelos to specific growth; 2 - Input a list of value of parameters used to describe the kinetcs ; 

3 - Compare results in the literature obtained in wine fermentation ;

Thank you for your comments.  As referenced in the paper, we recently published work in this journal that covers the topics you describe such as coupled ordinary differential equations, specific growth and kinetic parameters (https://doi.org/10.3390/fermentation10060269). We have also extended modeling to a large commercial dataset (https://doi.org/10.3390/fermentation11010004) and parameter estimation routines (https://doi.org/10.3390/fermentation10080386).

4 - In title contain the words "control", "modelling" and "control". Then, as the article is review article. I expected see many works related to it. 

 Thank you for you comment. The field of modelling and control of wine fermentation is small and, to our knowledge, we have included relevant works. Our previous recent paper goes into more details on wine fermentation modeling (https://doi.org/10.3390/fermentation10060269), therefore we only include a high-level discussion in this review paper.