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Answer: We are aware of the style requirements and we have applied all style requirements in the revised version. In addition to the improvements of the manuscript according to the reviews, a few additional modi-fications have been carried out:

- Tables 1–4 have been moved to the Supplementary Information, as they are not required for the immediate understanding of the manuscript’s contents.

- The boxplot diagram of experimental malt (former Fig 14) has been removed as its entire content was also present in the overview boxplot diagram (current Fig 16). The latter now also shows the taxa identified in the respective objects.

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- Fig 18 has been added in order to illustrate the possible genesis of the Hornstaad find.

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Reviewers' comments:

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Reviewer #1: Partly

Reviewer #2: Partly

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Reviewer #1: Yes

Reviewer #2: I Don't Know

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Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This is an interesting manuscript that proposes the hypothesis that thinned aleurone layers of cereal grains are a marker for germination of cereals by design (malting) for making beer. The subject is certainly of interest in the cultural evolution of humans.

Data to support this hypothesis have been assembled from charred plant remains obtained from five archaeological sites in Egypt and Europe, and from model experiments. Contextual evidence of beer making was presented for the two sites in Egypt. The data collection and analysis seem thorough, the manuscript is clearly presented and well written, and it tells a cohesive story. Measurements of the width of aleurone cell layers in charred, sprouted barley grains (implicitly obtained under malt-ing conditions) in the model experiments demonstrated a decrease in thickness over time, consistent with processes that occur during malting. The contextual evidence from the sites in Egypt, and the importance of beer in the pre-historic culture of this region, adds some weight to the proposal that the Egyptian samples provide evidence for malting and beer making. However in my opinion, the evidence from the archaeological samples from Europe is too sketchy to be indicative of beer brew-ing, and the evidence as a whole is insufficient to support a general claim of finding a marker that “can be considered in the research for ancient beer in any archaeological site where charred preser-vation occurs”.

Most “ancient beer” markers are quite remote from the actual fermentation process within the chaînes opératoires of beer making (such as: archaeological finds of implements, finds of sprouted grains), and some are even arbitrary (as calcium oxalate precipitates). Yet the combination of differ-ent independent markers/indicators adds up to some rather sound evidence of the general practice.

Answer: We have followed the reviewer's recommendation and have removed all statements that might have given the impression of an equation of aleurone thinning to beer. What we wish to emphasize is that this feature represents an entirely new possibility of unlocking sprouting (which is a core process in beer making). It is now more clearly stated that “thin aleurone = sprouted grain”. This new marker significantly adds up to the extant toolkit of ancient beer research as it is entirely inde-pendent from any other evidence typically used for finding hints on beer production. We have also modified the text in order to allow alternative interpretations to thin aleurone cell walls, induced by other factors, e.g. sourdough production.

We did, however, broaden the perspective on malt-based foodstuffs in general in the section “’Egyp-tian ale’ and ‘lakeshore lager’? Take them with a pinch of… malt!”. Interpretations of the central European malt finds have been “softened” towards a more general nature. The need for extensive ethnographical and historical overviews of malt foods is now expressed.

Sprouted grains (most likely affected by microbial activity) have been used as foods in many cul-tures for as long as grains have been cultivated.

We have modified our text for clarity, explaining the mechanisms behind the cell wall degradation. We have laid this out clearly in multiple instances of the manuscript, thoroughly supported by sound arguments and solid references:

• section “Cell wall degradation as a consequence of sprouting”

• section “A diagnostic feature hidden in plain sight?”

• section “Possible pitfalls in the interpretation of thin-walled aleurone tissue”.

A statement that malting was associated with food processing might seem more reasonable than linking it strongly to beer production, although that may have been an outcome.

Answer: We explicitly state the general nature of our finds in the manuscript in multiple instances, such as:

• section “A new look at charred finds of cereal products”, line 179 f: “at least as an indirect additional marker”

• section “A diagnostic feature hidden in plain sight”, line 213 f: “can serve as an indirect in-dicator of beer making “, and lines 229-230 f: “marker for malting, and albeit only indirectly pointing towards beer (…)”

• lines 626 f: “In contrast, the same aleurone thinning observed in the finds from the three central European Neolithic lakeshore settlements is not related to any clear evidence – be it contextual or artefactual – for brewing activities. So, how much of a hard proof for brewing do we really have?”

• and the following paragraphs

We have also broadened the perspective on malt-based foodstuffs in general in the section “’Egyp-tian ale’ and ‘lakeshore lager’? Take them with a pinch of… malt!”. The possible use of sourdough was also mentioned on several occasions in the text.

A greater concern I have relates to ancient cereal grains being much smaller than those from mod-ern varieties (e.g., Ferrio et al. 2006. J Cer Sci44, 323-332; Helbelstrup 2017. Plant Sci 256, 1-4).

Answer: We cannot agree with this claim and give following arguments:

1) We have added a discussion on aleurone composition and its relation to environmental con-ditions as well as to differences in species and landraces. However, the thickness of aleurone cell walls is apparently neither a function of grain size, nor of any of the aforementioned factors. The paper by Hands et al. 2012 e. g. demonstrates quite impressively that even small-seeded wild Poaceae do indeed have massive aleurone cell walls. Although we cannot completely exclude every other potential factor causing aleurone thinning (which is, of course, epistemologically impossible), our criterion has a strong diagnostic value within the given examples and is based on sound arguments and congruent observations.

2) In support of our arguments, we may bring to Reviewer`s 1 notice that the paper by Hebel-strup 2017 actually refers to wild versus domesticated forms, and to the beginnings of do-mestication in the Near East, at least 5,000 years earlier than in the sites mentioned in the current manuscript. We need not go into detail much more, but happily support the referee with a standard literature reference for further lecture (Zohary, D., M. Hopf, and E. Weiss, eds., 2012, Domestication of Plants in the Old World).

3) In the same supportive spirit, we may point out that the paper by Ferrio et al. 2006 uses grain weight on charred archaeological seeds, interpreting different grain sizes as conse-quences of growth conditions (!) and neither implies any (pre-)historical taxonomic traits nor a connection between grain anatomy/histology and grain size as suggested by the refer-ee.

The measurements taken from all of the archaeological samples, showed aleurone layers of similar thickness, but significantly smaller than those from the modern grains. This observation could be explained as structures coming from small grains rather than being indicative of germination.

Small grains even of other Poaceae species do not have thinner cell walls in general than e. g. culti-vated barley (see above). Triticum aestivum is among the exceptions, which has been dealt with in the manuscript. We have brought forward (see section “Cell wall degradation as a consequence of sprouting” and references cited there), that the progressive thinning of aleurone is a function of a) sprouting time, and b) the position of the observed aleurone within the germinating grain. We have explained these facts in the manuscript. For Reviewer 2, an outstanding researcher and number one expert in the field, all this was perfectly legible, comprehensible, and stringent in its argumentation.

However, following up Reviewer 1’s comments and Reviewer 2’s explicit request, we also added measurements of synchronous “reference” remains of ancient processed cereal foodstuffs displaying normal cell wall thicknesses in the aleurone layer. These samples may serve as a rebuttal to the aforementioned claim, and also as a data source strengthening the differentiation between different food types from the same site.

Grains are naturally associated with many active microbes, which as pointed out, could have caused the morphological changes. Hence, I am not persuaded by the statement of “thinned (degraded) aleurone cell walls as a general new marker for recognizing malting in cereal products from archae-ological contexts”.

Answer: We have elaborated in very detailed ways why microbial changes can be ruled out as the causes of cell wall thinning (see above).

We want to express our concern about Reviewer 1’s statement of being “not persuaded” without bringing forward any further substantial evidence or reason, aside from the claims which we have already refuted above. In our opinion, this is not sufficient for a qualified scientific debate.

Overall, I find the manuscript could make a useful contribution to this interesting area of prehistoric human activity if the discussion, conclusions and abstract are recast and softened to be more bal-anced to alternative interpretations. The title is cumbersome and should be shortened … at the least, I suggest omitting the words “and comprehensive” and the words after “record”.

Answer: We have extensively elaborated on all possible and probable alternative interpretations (also ac-cording to Reviewer 2). We have thoroughly explained why we think that some of them can work, and others cannot.

We have followed Reviewer's 1 recommendations and thus rephrased several statements in the ab-stract, discussion and conclusions in order to achieve more balanced appearance of our manuscript, and “soften” some of the argumentation.

The title has now been shortened.

I also recommend the following minor editorial corrections.

1. The statement that the main protein content in cereal grains is in the aleurone layer (p6, line 185) is incorrect; aleurone cells contain protein bodies, but the majority of cereal grain proteins are stor-age proteins in the endosperm.

Answer: We have modified this accordingly.

2. The term “heterocelluloses” is inaccurate and not meaningful; it should be replaced by heteropol-ysaccharides.

Answer: We have exchanged “heterocelluloses” by the term “hemicelluloses” which is even more accurate and meaningful than “heteropolysaccharides”.

Reviewer #2: This paper presents an important advance in the detection of malting in ancient sam-ples, moving beyond starch characteristics that usually disappear during charring. The aleurone layer often survives charring and is recognisable under SEM, meaning that the proposed criterion can be widely applied to charred and uncharred residues. The ability to detect malting in a wide range of archaeological contexts has the potential, as demonstrated through the case studies, to sig-nificantly advance our understanding of the dietary and social roles of food in ancient societies.

The paper is well-grounded in the literature of brewing science and extensive experimentation. Data is fully presented in the supplementary files and technical aspects of methodology are fully ex-plained. Alternative explanations are fully considered. Although I make some suggestions on meth-odology below, I would expect the requested additional information to confirm the results of this study.

My suggestions for major changes are as follows:

Control samples:

- For the experimental work, I could not see the figures for aleurone thickness for the Heinrich Durst Malzfabriken barley grains *before* malting, either in table 1 or elsewhere – did I miss them? In the case of wheat, where there are control (unmalted) grains and malted grains (line 274), I could not find the aleurone thickness reported in the paper. For both wheat and barley it’s hard to assess the evidence for the effects of malting without seeing the measurements for malted vs unmalted grains.

Answer: The basic aim of the paper is not to demonstrate that malting has any effect on cereal aleurone cell wall thickness, as the basic research on this topic has been carried out decades ago (cf. introductory chapters). Our goal was to raise awareness, and significance, of this phenomenon in archaeobotani-cal materials, and to test whether the cell wall thinning can also be observed in charred state. This has been explained more clearly now in the research goals section.

We left out entirely unmalted barley grains due to the fact that measurable loss in cell wall sub-stance is not observable in the first day of malting. This has now been more explicitly stated in the section “Experimentally charred malt”.

- For the ancient residues, it should be standard practice to compare residues from ‘likely’ contexts with those from ‘unlikely’ contexts. For example, when evidence of food only occurs in association with food-related objects and is absent from tested non-food related objects or soil matrix, it strengthens the case for the age and identification of the food residue. In this instance the control sample could be grains from the sites or periods concerned that are intact and do not show signs of germination. Would it be possible to present some data on aleurone thickness from intact charred grains from the European sites? And for the Egyptian sites (material harder to access) at least from uncharred grains of a similar date in accessible collections. As with the experimental samples, com-paring measurements for likely-malted vs unlikely-malted would strengthen the authors’ case.

Answer: For two of the three central European sites (Sipplingen and Zürichsee), other processed food resi-dues are available which do not show the cell wall thinning, and therefore likely derive from un-malted grains. These are now included into the data, their characteristics are explained.

Beer vs malted foods

135, Fig. 1 and various points in the manuscript. I think you could strengthen the distinction be-tween mashing and fermenting (probably should be distinct steps in Fig 1). *It is only the last step that produces alcohol and is evidence for beer.* The criterion of the thinning of the aleurone layer is, if I understand correctly, evidence of saccharification, not of fermentation?

Saccharification (during malting) is now more explicitly shown as a separate process in Fig. 1. How-ever, saccharification does continue during fermentation, which has now also been clarified in Fig 1. The aleurone thinning is a marker for malting/sprouting/saccharification. This is now more clearly explained in the text in section “Defining core processes of beer making”.

- It might be worth adding a heading to explore the circumstances in which evidence of malting and grinding can be interpreted as evidence of beer. Of course human nature and Occam’s razor sug-gests this is often the case, but at the same time there is a risk inherent in projecting our current in-terest in beer back into the past. For example, in the paragraph starting 503, for example, one residue has a liquid appearance, leading to all being interpreted as beer. But couldn’t this be a malt drink? And the non-liquid food, malt foods? There is a strong tradition in several parts of the world of malted foods or beverages, notably in connection with weaning, and with millets in Africa. It would be worth adding a paragraph to explore this – there is plenty of literature on malted foods. What does the record look like for traditional food cultures in Europe? If malted foods and drinks are ab-sent it strengthens the case for beer. Adam Maurizio might be good for this.

Answer: We have added examples of other malt-based food than beer from the (ethno-)historical literature, stating that malt finds lacking a clear brewing-associated context will require more caution for their interpretation. Conclusions towards beer have been rephrase now for the central European malt finds. We now are pointing out that a concise overview of malted foodstuffs in the Old World is a big desideratum for research, in order to provide a reliable source of comparative data for archaeo-logical remains of malt-based foodstuffs.

Another example is at 523 “As beer brewing based on sprouted grains is ubiquitous in the ethno-graphic, historical, and archaeological record, probability is very high that these remains indeed represent Neolithic beer mash.” is another example of projecting the ubiquity of beer today into the archaeological record, creating a self-fulfilling cycle. In general in the discussion section I found the distinction between malting and fermentation inconsistent – would be worth careful review and rewording.

Answer: We have changed this accordingly (see similar issue raised above).

Minor suggestions

43. The first two paragraphs of the abstract are essentially introductory text from the main text. I would suggest rewriting the abstract following the standard structure set out at: https://www.wiley.com/network/researchers/preparing-your-article/how-to-write-a-scientific-abstract

Answer: The abstract has been rewritten accordingly.

61. keywords – no need to repeat words already in the title.

Answer: The title has been shortened, now there are no more overlaps with the keywords

107. Suggest reword “no scientifically clear answer to the question how the ancient beer was made” as it is not really a single question. Maybe “Our knowledge of the occurrence and manufacture of ancient beer is highly incomplete”?

Answer: Changed accordingly.

117. Briefly define saccharification at this point.

Answer: Changed accordingly.

136. The manuscript would benefit from copy-editing by a native English speaker, e.g. for text such as “The diagram bases on historical and ethnographic records” – better as “…is based on…”

Answer: Language editing by a native English speaker has been carried out.

153. For accessibility I suggest avoiding Latin terms (except when essential terminology)

Answer: See above.

167. ACO is only used twice in the text so I suggest it is discarded as an unnecessary abbreviation (from the keywords too).

Answer: We have placed the acronym into the paper on purpose: There will be a paper on diagnostic ap-proaches towards amorphous charred objects (ACO), and we would really like to promote this acro-nym as parts of a coming “standard terminology” for such kinds of material. Following the review-er’s suggestions, we have now included ACO in multiple instances.

403. Table 1 needs full caption.

Answer: The tables have been partly merged, partly moved into the Supplementary materials. We hope all captions are now satisfactorily written.

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Reviewer #1: No

Reviewer #2: Yes: Mark Nesbitt

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