Referee's Comments

THE AUTHORS have attempted to define an objective standard for the usefulness of a chocolate teapot based on experimental measurements. Although this is a laudable undertaking the authors have only been partially successful in their aim. There are a number of problems with their approach:-

1.  For any standard method it is necessary to have data which are statistically robust. The authors describe a single experiment with one chocolate teapot and make no attempt to investigate variability and reliability within a single chocolate teapot grade or the grade to grade variation between chocolate teapots from different suppliers. The behaviour observed may have been specific to the teapot tested. Only a much larger research programme could determine if these results are representative.

2.  The authors use the term "chocolate" as if it were a single material of well-defined composition and properties. However, the preferred type of chocolate varies from country to country; for example common UK and US chocolate tastes are different and the rest of Europe hates both of them [2]. The taste and physical properties of chocolate are controlled by the chemistry of the material and its micrometer-scale structure, which generally consists of particles ranging from 10mm to 120mm [2]. This detailed structure depends on the percentage of cocoa solids and the precise processing sequence used in its manufacture. Although the authors identify a manufacturer, which might allow other workers to gain access to process information if they wish to repeat the experiment, they do not define the base composition of the chocolate used. At least the cocoa solids percentage should be quoted.

3.  The authors' use of consumer-grade H₂O is not recommended as it is a highly contaminated solvent. Whilst there is no doubt that this did not influence their test results in this study, the composition of consumer-grade material is very variable and this could be an important factor in more controlled studies. The tea bag is a similar variable since control of the tea composition in the bag cannot be relied on. Care must also be taken to avoid flavoured teas such as Earl Grey which contain oils that react with cocoa butter. Full analysis of water, tea and teabag materials should be reported in all future studies.

4.  To derive maximum benefit from the chocolate teapot as a comparison standard it is necessary to have a fully quantitative test of usefulness that may be used to rank the relative usefulness of other systems. In the authors' study the use of water at ~97°C will lead to very rapid failure of the chocolate teapot since it is well-known that the highest melting point cocoa-butter polymorph[1] melts at 36.3°C [1]; tests which lead to such catastrophic failure are not good for ranking purposes.

Following the seminal work of Professor Thornton and co-workers at the University of Bournville [3], an alternative experiment is suggested requiring more apparatus but which will give the quantitative measure necessary. A small heater and thermocouple system is placed in the teapot together with a controlled amount of cold water. An electrical controller linked to the thermocouple supplied current to the heater which gradually heats the water at a controlled rate. The temperature is ramped up until teapot failure occurs and the failure temperature is recorded. The chocolate teapot utility ratio would then be defined as the ratio of the failure temperature to 97°C and for a typical tempered chocolate would be about 0.35 [4]. Any process with a usefulness ratio of less than this figure could clearly and unambiguously be described as less useful than a chocolate teapot.

In summary the authors have opened a useful research area which would need a large programme of research and several hundred chocolate teapots to deliver a sensible standard. This referee has a fully equipped laboratory which is ideally suited to such research and would welcome the donation of an initial batch of (say) fifty teapots for scoping trials.

References

[1]  J. Schlichter-Aronhime, S. Sarig and N. Garti, "Reconsideration of polymorphic transformations in cocoa butter using the DSC," J. Am. Oil. Chem. Soc., 65 (1988) 1140.

[2]  P. Fryer and K. Pinschower, "The Materials Science of Chocolate," Materials Research Bulletin, 25 (2000) 25.

[3]  C. Thornton, H. Cadbury, O. Suchard and C. Nestle, "The use of processed cocoa butter for fire protection," J. Env. Choc. Technology, 7 (1997) 123.

[4]  S.J. Bull, D.A. Bull, P.M. Bull , A.D. Bull and C.R. LeSueur, unpublished work (2001).

It is usual that referees remain anonymous when considering submissions for major journals. However, under the circumstances, I see no problem in identifying myself.

—Dr Steve Bull
Department of Mechanical, Materials and Manufacturing Engineering, University of Newcastle

[1]This polymorph is actually formed after long term exposure of the chocolate at room temperature (bloomed chocolate); as-received tempered chocolate will melt at 33.8^oC.

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