A Sustainable Approach Based on the Use of Unripe Grape Frozen Musts to Modulate Wine Characteristics as a Proof of Concept

Round 1

Reviewer 1 Report

The topic of the manuscript is very interesting, the idea for application of unripe grapes for wine acidification is innovative and a lot of work was done. However, there are a lot of things that has to be improved in order to increase the manuscript quality.

1. The title of the manuscript is too long and according to me you have missed the word "grape" between "unripe" and "frozen"

2. There are a lot of unnecessary information in Introduction (till ln. 65) and it is to some extent chaotically written. According to me it will be better to start with grape chemical composition, how climate changes affect to it, what are the common practice to correct acidity in wine making, to write something to unripe grapes and the sustainability, and the unripe grapes application in acidity correction.

3. Materials and methods - Please, explain how you have chosen 440 ml unripe grape frozen must? Is it equal to 19 ml of organic acids mixture? The text is a little unclear and I can't understand when you make acidification after fermentation or before? SO2 is placed in the wines or in the musts? Why you used mix of 2 commercial strains?

4. Results and discussion

It will be better if Figures and Tables are situated near the text which discussed them. Table 1 will be better if contains not only corrected wines parameters but also of the control sample.  I can't understand what is the reason for Table 2 to be in the manuscript? In Table 4 it will be better to give the dimensions of the volatile compounds

Author Response

Reviewer 1:

1. The title of the manuscript is too long and according to me you have missed the word "grape" between "unripe" and "frozen"

R: We have change the title according to Reviewer 1 because the word “grape” was indeed missing. Considering the Reviewer 2 considerations, “proof of concept” was added to the title.

2. There are a lot of unnecessary information in Introduction (till ln. 65) and it is to some extent chaotically written. According to me it will be better to start with grape chemical composition, how climate changes affect to it, what are the common practice to correct acidity in wine making, to write something to unripe grapes and the sustainability, and the unripe grapes application in acidity correction.

R: The introduction was fully restructured according to review suggestion. The Introduction in now much smaller and better structured. All references were also corrected considering the text that was eliminated.

3. Materials and methods - Please, explain how you have chosen 440 ml unripe grape frozen must? Is it equal to 19 ml of organic acids mixture? The text is a little unclear and I can't understand when you make acidification after fermentation or before? SO2 is placed in the wines or in the musts? Why you used mix of 2 commercial strains?

R: The paragraph was rewritten to make it clearer. Indeed adding frozen must and a Mix solution of organic acids were performed to adjust the final acidity to around 6g/L (TA). SO2 was added prior alcoholic fermentation. Regarding yeasts, this is a commercial mixture of two Sacharomyces cerevisaea already used before by our team with good results in white wine small fermentations (please see Almeida Santos et al 2022. https://0-doi-org.brum.beds.ac.uk/10.1051/ctv/ctv20223701039)

4. Results and discussion

It will be better if Figures and Tables are situated near the text which discussed them. Table 1 will be better if contains not only corrected wines parameters but also of the control sample.

1. We added values for control wines that of course, existed but somehow were missed. We apologize for the mistake

I can't understand what is the reason for Table 2 to be in the manuscript?

1. The table is indeed not necessary, and in this revised version it was removed

In Table 4 it will be better to give the dimensions of the volatile compounds

1. The values correspond to average peak area values. This is now in the revised version, in the table legend.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript reports a simple practical approach to adjust the acidity of white grape must commonly needed in winemaking, particularly in warm regions. Regretfully (i) the approach is not new (see literature for previous research), (ii) the trials are limited in type (one variety and one vintage only), size (few litres), and numbers (6 trials), (iii) the post-hoc ANOVA findings are doubtful considering the values of SD (943±128^b  vs  929±142^b  vs  1083±261^a) and the multivariate approach is questionable due to unbalanced matrix (6 samples with over ten times variables), (iv) the literature data on Odour Activity Values (OAVs) are missing, and comparison with VOCs peak area is useless due to inconsistency between unit of measurement (as appropriate example of data info see: Molecules 2019, 24, 2978; doi:10.3390/molecules24162978).

The many important shortcomings listed above makes the manuscript more suitable for technical (non-scientific) publication, therefore I recommend rejection from Beverages and resubmission to another technical Journal. In this view, there are a number of further technical lacks that need to be addressed before submission to another Journals, including the data of control wine (testimonial) in Table 1.

Author Response

Reviewer 2:

The manuscript reports a simple practical approach to adjust the acidity of white grape must commonly needed in winemaking, particularly in warm regions. Regretfully (i) the approach is not new (see literature for previous research), (ii) the trials are limited in type (one variety and one vintage only), size (few litres), and numbers (6 trials),

R: As far our knowledge there is no literature that describe the acidity modulation the way the authors described in this work. Although a proof of concept (now introduced in the title of the paper), this approach worked very well for this wine variety. Further research is being made by the team with other varieties and blends and also vintages. Considering the breakthrough given by this work, we must disagree when it is said that the approach is not new. Actually, considering the literature, the authors do not share the same opinion. 

(iii) the post-hoc ANOVA findings are doubtful considering the values of SD (943±128b  vs  929±142b  vs  1083±261a)

R: Results from ANOVA test. Samples: 1 – UM*; 2- Mix* and 3 – T*.

This is a table directly from statistical output. As a result of this analysis the significant differences mentioned in table, (943±128b vs  929±142b  vs  1083±261a) are correct. One can see that T* wines are significantly different from UM* and Mix* wines, that, regarding this parameter, are not significantly different between them.

and the multivariate approach is questionable due to unbalanced matrix (6 samples with over ten times variables),

R: We agree with the reviewer. This PCA was thus removed and the text revised accordingly.

 (iv) the literature data on Odour Activity Values (OAVs) are missing, and comparison with VOCs peak area is useless due to inconsistency between unit of measurement (as appropriate example of data info see: Molecules 2019, 24, 2978; doi:10.3390/molecules24162978).

R: OAVs were not calculated, since only a semi-quantitative approach was performed based on the percentage of peak area. VOCs were studied and compared, if present differently, among wines. There is no inconsistency between unit of measurement, since HS-SPME was performed and not SPE as sample preparation methodology.

The many important shortcomings listed above makes the manuscript more suitable for technical (non-scientific) publication, therefore I recommend rejection from Beverages and resubmission to another technical Journal. In this view, there are a number of further technical lacks that need to be addressed before submission to another Journals, including the data of control wine (testimonial) in Table 1.

In light of all the corrections that we have introduced we do believe that our research, as a proof of concept, is valuable and worthy to be published in beverages. The research presented here can be regarded as a first step to promote circular economy by taking advantages of must from green grapes, that are harvest to the soil, into a product that can be used successfully to increase must (and wine) acidity using the vine own resources, as already highlighted in the conclusion.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have corrected manuscript according my suggestion. In Table 1 it will be better to have also the results of wine with organic acids addition. Table 3 still remains unclear.

Author Response

Reviewer 1

The authors have corrected manuscript according my suggestion. In Table 1 it will be better to have also the results of wine with organic acids addition. Table 3 still remains unclear.

R:

In Table 1 the legend is now more detailed

“Average values for oenological parameters for all Antão Vaz wines. Frozen unripe grape must addition (UM); addition of a mixed solution of tartaric, malic, and lactic acid (Mix) ; testimonial wine (T).”

In Table 3 the legend is now more detailed

“Table 3. Average area values of VOC obtained from the analysis of all Antão Vaz wines and respective standard deviation of the mean: Frozen unripe grape must addition (UM); addition of a mixed solution of tartaric, malic, and lactic acid (Mix) ; testimonial wine (T). LRI denote calculated linear retention indices; LRI (Lit) denote linear retention indices according to literature; Aroma descriptor denote the aroma descriptors indicated by the literature.”

Author Response File: Author Response.docx

Reviewer 2 Report

Several study investigated the topic, and few of them were included in the manuscript already (doi: 10.1111/j.1755-0238.2011.00142.x; https ://doi.org/10.1007/s0021 7-018-3045-0) whereas other are missing, including:

DOI 10.1002/jsfa.8434

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2018.04.013

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodres.2018.04.057

DOI:10.20870/oeno-one.2020.54.4.4018

http://0-dx-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2017.10.024

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2018.03.118

Although the former studies apply to red grape, they represent a valuable example of sound experimental trials, including the quantitative measurement (μg/L) of volatile compounds in wines.

The average peak area is almost useless without OAVs values, therefore move Table 3 in Supplementary Material.

Table 1 and 2: report mean and standard error of the mean (not standard deviation).

Line 166: remove PCA.

 Author Response

Reviewer 2

Several study investigated the topic, and few of them were included in the manuscript already (doi: 10.1111/j.1755-0238.2011.00142.x; https://0-doi-org.brum.beds.ac.uk/10.1007/s0021 7-018-3045-0) whereas other are missing, including: DOI 10.1002/jsfa.8434;

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2018.04.013;

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodres.2018.04.057;

DOI:10.20870/oeno-one.2020.54.4.4018;

http://0-dx-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2017.10.024;

https://0-doi-org.brum.beds.ac.uk/10.1016/j.foodchem.2018.03.118;

Although the former studies apply to red grape, they represent a valuable example of sound experimental trials, including the quantitative measurement (μg/L) of volatile compounds in wines.

R: According to reviewer suggestion all references were included in order to enrich the document with information also with red wines literature. New reference numbering was performed accordingly. For warm climates (like Portugal), acidification of white wine is indeed an issue, and that was the reason why our work aimed a Portuguese white wine variety. Red wines were not aimed in this work, but the information can be valuable for future work in this domain, especially in what semiquantitation regards. Indeed several studies used SPME as sample preparation method. Despite the use of isotopically marked internal standards, HS-SPME quantitation stills a controversial topic.

The average peak area is almost useless without OAVs values, therefore move Table 3 in Supplementary Material.

R: The authors do not agree with the reviewer. Indeed the average peak areas are still important since reflect a dominance trend of some compounds over others, even if MS is used. In our opinion Table 3 should be present in the main document, also to help the readers of Beverages to clearly identify the compounds discussed further in the document.

Table 1 and 2: report mean and standard error of the mean (not standard deviation).

R: The authors corrected in Table 1 and 2 the reviewer observation, which is very pertinent and correct.

Line 166: remove PCA.

R: The authors still maintained PCA, since indeed it is a PCA we are discussion about.

Author Response File: Author Response.docx