Calculating the optimum temperature for serving hot beverages
Introduction
The high temperature range typically recommended for serving hot beverages commercially (recommended to be on the order of 185 °F (85 °C)) presents a substantial scald burn hazard to consumers [1], and many such injuries occur annually [2], [3]. A reduction in the number and severity of these injuries has been a long-standing objective within the burn prevention community. One step toward that goal is to construct an analysis tool that can be used to predict the quantitative effect of altering the beverage temperature on changing the potential for scald injury.
The propensity for hot liquids to produce burn injuries to skin has been measured and modeled for more than a half century [4], [5]. These analysis tools were accepted and applied very widely within the biomedical engineering and science community. Based on experimental and computationally derived data, it is very straightforward to predict the benefit in reduced injury potential that would be gained by lowering the service temperature of hot beverages. The incremental benefit is largest at the highest temperatures owing to the exponential dependence of the rate of injury on the absolute temperature. The obvious conclusion is that the lower the serving temperature, the less is the potential for causing a burn in the case of a spill accident.
However, it is not possible to reduce the temperature of a hot beverage without limit because at some point consumers will discern that their hot beverage is not warm enough to satisfy their expectations. It should be anticipated that for a population of users a spectrum of preferred drinking temperatures would be identified, with some being hotter and some colder than the average value. If a threshold temperature range for satisfaction can be identified, then higher values would have the combined effects of increasing burn hazard and decreasing consumer satisfaction, both of which are undesirable. At sub-threshold temperatures, injury potential would continue to be reduced, as desired, but consumer satisfaction would be compromised. Identifying the incremental contributions of a change in beverage temperature (as a function of the absolute value of temperature) to altering the scald hazard and the product quality is one of the primary challenges addressed in this study.
Coffee is an extremely popular beverage. Nearly 8 of 10 Americans drink coffee, consuming more than 300 million cups per day, many of which are served commercially. The National Coffee Association of U.S.A., Inc., recommends that the temperature of a coffee must be maintained between 180 °F and 185 °F (82.2 °C and 85 °C) for optimal taste [6], [7]. This recommendation has carried considerable influence in establishing the policies for serving temperatures for many commercial vendors.
In contrast to this recommended serving temperature, data has been published recently that identifies an average of approximately 140 °F (60 °C) as the temperature at which consumers prefer to drink coffee [8]. A group of 300 subjects were enabled to adjust their coffee temperature by adding condiments and dilution with cooler beverage to achieve drinking conditions they considered most favorable. For this study group the standard deviation in drinking temperature was about ±15 °F (8.3 °C). The preferred drinking temperature is considerably lower than is traditionally recommended for serving coffee, and such a reduction would have a major impact on lowering the number and severity of scald burns caused by hot beverage spills.
The challenge addressed in this study is to identify an algorithm for combining the quantitative thermal effects of reducing scald burn hazard while maintaining consumer perceived product quality. Quantitative measures of how temperature influences both of these phenomena are developed individually and then combined into a single metric for optimization of serving temperature.
The hypothesis of this study is that a tradeoff can be defined in specifying hot beverage serving temperatures whereby a compromise is achieved in reducing scald burn hazard while maintaining acceptable product quality.
Section snippets
Scald burn model
This paper addresses the issue of how the current serving standards for coffee could be adjusted based on consumer taste preference to provide a level of protection to individuals from scald burns. The analysis approach adopted is to simulate the injury process using an Arrhenius-kinetics based mathematical model for molecular damage, as postulated more than a half century ago by Henriques and Moritz [4], [5] and Büttner [9], [10], to describe and predict thermal insult effects in skin. The
Preferred coffee drinking temperature data
Lee and O’Mahony [8] recently published data from a study to determine consumer preferences for the drinking temperature of coffee. Large cohorts adjusted the temperature of their coffee by mixing from hotter (85.0–90.6 °C) (185–195.1 °F) and cooler (21.1–23.8 °C) (70–74.8 °F) sources. Two separate experiments were conducted. One cohort (n = 300) also had the opportunity to add condiments, which contributed to adjusting the temperature, whereas the second (n = 108) all drank black coffee. The summary
Combined temperature metric
A major challenge of this study is to develop an algorithm that provides a rational basis for comparing the influence of beverage temperature on causation of scald burns and on consumer product satisfaction. For purposes of this analysis, consumer product satisfaction as reflected in preferred drinking temperature of hot coffee is referred to as quality. Since the burn is a negative event, it is logical to view coffee temperature in terms of a metric that reflects consumer dissatisfaction (also
Discussion
By applying the FoD criterion, an optimal drinking temperature of approximately 136 °F (57.8 °C) is defined. However, since the FoD as a function of temperature passes through a minimum value in this region, the slope of the curve is zero or at values close to it. Thus, it is not appropriate to specify a distinct value for the optimal temperature. Rather, a range of temperatures can be identified for which the FoD is close to its minimum value. This range extends from approximately 130 °F to 140 °F
Conclusions
This study has demonstrated that it is possible to define an algorithm whereby one can combine balanced considerations of realistically minimizing scald hazard from a spilled hot beverage with maintaining a standard of product quality acceptable to consumers so as to establish an optimal serving temperature (or range of temperatures) for hot coffee. The underlying considerations for both scalding and product quality are based on objective, documented scientific data. Application of this data to
Conflict of interest statement
Neither author has any financial or personal relationships with other people or organizations that could inappropriately influence or bias their work on this manuscript.
Acknowledgements
This study was supported in part by the Robert M. and Prudie Leibrock Professorship in Engineering at the University of Texas at Austin.
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