Managing Cancer Risk from Very Hot Beverages: Influence of Brewing Temperature on Sensory Characteristics of Coffee ^†

Abstract

In 2016, the International Agency for Research on Cancer (IARC) classified the drinking of very hot beverages above 65 °C as “probably carcinogenic to humans” (Group 2A), with esophageal squamous cell carcinoma (ESCC) particularly associated with the habit. As this finding may have practical implications for the coffee industry, there appears to be a need to critically reassess the often extremely high standard brewing and serving temperatures used in coffee preparation. This study presents a summary of the most recent IARC assessment on very hot beverage consumption and investigates the influence of brewing temperatures (80, 86, and 93 °C) and roasting degrees (light, medium, and dark) on the sensory profile of manual drip coffee. As the evidence linking very hot beverage consumption to increased ESCC risk has grown stronger, the IARC classification is likely to be upgraded in coming years. As the roast intensity increased, assessors preferred coffees brewed at lower temperatures and most of them were not able to distinguish brews extracted at different temperatures. Given these results, the potential for lowering the brewing temperature in commercial settings is clear. This approach not only enhances consumer safety, but also positions businesses as leaders in health-conscious practices, potentially redefining standards across the industry for the optimal temperature of coffee serving that aligns with both flavor and health research findings.

1. Introduction

Coffee is one of the most widely consumed beverages globally, with its preparation and consumption deeply ingrained in various cultures [1]. However, recent scientific findings have raised concerns about the potential health risks associated with consuming very hot beverages, including coffee. In 2016, the International Agency for Research on Cancer (IARC) classified drinking very hot beverages above 65 °C as “probably carcinogenic to humans” (Group 2A) [2,3]. This classification has significant implications for the coffee industry and consumer health.

The relationship between high-temperature beverage consumption and an increased risk of esophageal squamous cell carcinoma (ESCC) has been further strengthened by recent epidemiological evidence [4]. This association is particularly pronounced when combined with other risk factors such as tobacco use and alcohol consumption. The underlying pathophysiological mechanisms involve thermal injury to the esophageal epithelium, which can induce cellular proliferation, cause chronic inflammation, and ultimately promote carcinogenesis [3,4].

These findings challenge long-standing practices in the coffee industry, particularly the use of extremely high standard brewing and serving temperatures. While only limited information is available regarding serving temperatures in the food service sector, one notable source of data comes from legal proceedings against a major US fast food chain, which revealed that coffee was served at temperatures ranging from 75 to 88 °C, with variations depending on the specific dispensing equipment [5]. A more recent survey in Germany has shown that the average dispensing and serving temperatures in both households and commercial settings are around 75 °C, ranging from 58 °C to 88 °C [6]. This preference for higher temperatures could be influenced by consumer habits and the desire for the beverages to remain hot for a longer period after serving. In Brazil, a study measured serving and drinking temperatures in Rio de Janeiro and Petrópolis, evaluating 703 coffee beverages. Serving temperatures ranged from 50.5 °C to 94.5 °C in Rio and from 52.4 °C to 87.7 °C in Petrópolis, with averages of 73.8 °C and 71.7 °C, respectively. In Rio, 26% of consumers drank coffee at temperatures ≥65 °C, and 9% at ≥70 °C. In Petrópolis, 60% consumed coffee at temperatures ≥65 °C and 19% at ≥70 °C [7]. Another study in João Pessoa, Paraíba, evaluated serving temperatures in 100 food service establishments. This study included both coffee shops (CS) and low-cost food service establishments (LCFS) to represent diverse socio-economic backgrounds. The serving temperatures were, on average, 90% and 68% above 65 °C in LCFS and CS, respectively, with median values of 77 °C in LCFS and 70 °C in CS [8]. Such excessively high temperatures are sometimes favored as a method to address potential microbial contamination [9]. However, research indicates that temperatures exceeding 55 °C are typically adequate to mitigate such risks [10]. Hence, there is a growing need to re-evaluate these practices in light of the potential cancer risk associated with very hot beverages.

This paper examines the current evidence on the health risks of consuming very hot coffee and assesses the influence of brewing temperature—in combination with roast degrees—on the sensory profile of coffee. By addressing these issues, the authors aim to contribute to the ongoing dialog about optimal coffee preparation and consumption practices, potentially reshaping industry standards to better align with both flavor preferences and health considerations.

2. Summary of the Most Recent International Agency for Research on Cancer (IARC) Assessment on Very Hot Beverage Consumption

According to the recent 2024 IARC priorities working group [4], epidemiological studies face challenges in accurately assessing exposure to hot beverages. Key issues include distinguishing between brewing and serving temperatures [11] and the limitations of self-reported drinking temperatures [12]. To address these concerns, researchers have developed more objective metrics by incorporating additional factors such as sip volume, temperature during consumption, drinking patterns, and frequency of oral burns. These efforts provide a more comprehensive understanding of the potential health impacts associated with hot beverage consumption [4].

Since the IARC Monographs Volume 116 meeting in 2016, which noted a consistent association between hot beverage consumption and increased ESCC risk based primarily on case–control studies [3], additional cohort studies have emerged [4].

The Golestan Cohort Study in Iran, following 50,045 individuals for a median of 10.1 years, found that hot and very hot black tea consumption increased ESCC risk by more than two- and eight-fold, respectively, compared to warm tea. This study’s design, using warm tea drinkers as the reference group and employing both objective and self-reported exposure metrics, strengthened its findings [13].

Another prospective cohort study in China, involving over 450,000 participants followed for a median of 9.2 years, revealed that combining high-temperature tea consumption with alcohol or smoking increased esophageal cancer risk more than hot tea alone. However, this study relied on self-reported baseline tea consumption and focused primarily on interactions with alcohol and smoking [14].

Recent population-based case–control studies in China [15,16,17] and Africa [18,19] have consistently shown strong positive associations between beverage temperature and ESCC risk [4]. The African studies, being the first reports from that region, provide valuable data on the consistency of this association across different populations [4].

Additionally, two recent meta-analyses, one including 23 reports (5050 cases, 10,609 controls) and another comprising 12 case–control studies (5253 cases, 8273 controls), have confirmed that hot beverage consumption significantly increases ESCC risk [20,21].

Recent mechanistic studies related to the key characteristics of carcinogens are limited [4]. Ernst et al. [22] investigated the effects of hot beverage consumption on oral mucosa cells in 73 participants from Northern Iran. They observed increased cell division, but not DNA damage (measured by micronuclei frequency), in subjects consuming ≥3 cups of hot beverages daily for 21 days. Wang et al. [23] used various ESCC models (in vitro and in vivo) to demonstrate that hot water (65 °C) can induce cell proliferation and promote the progression of non-neoplastic lesions to malignant phenotypes. This process was associated with the expression of miR-132-3p, a microRNA known to be highly expressed in various cancer types.

All in all, since IARC Monographs Volume 116 [3], the evidence linking very hot beverage consumption to increased ESCC risk has grown stronger. This is supported by findings from a highly informative cohort study and several case–control studies conducted across diverse geographical regions [4]. Given these developments, the IARC priorities working group suggested a reconsideration of the IARC Monographs classification for very hot beverages. The priority for re-evaluation was considered high (<2.5 years) [4,24]. According to the authors’ judgment, the available evidence would probably allow for an upgrade to an IARC group 1 carcinogen (i.e., the highest level of evidence for carcinogenicity in humans).

3. Influence of Brewing Temperatures on Sensory Profile of Coffee

A simple opportunity to lower the serving temperature of coffee is via a reduction in brewing temperature. However, studies looking at the effect of brewing temperature on the sensory profile of coffee are limited. One exception is a 2020 study in which different brewing temperatures (80 °C vs. 128 °C and 80 °C vs. 93 °C) of espresso coffee were compared in sensory trials using triangle test methodology [25]; it was shown that most tasters were unable to distinguish between coffees brewed at 80 °C and 90 °C, but the possible role of roast degree was not investigated in the sensory trials. With the recent improvement in coffee quality worldwide, the preference for milder coffees has increased and the attribute of bitterness is not as preferred as before, especially among those who can purchase machine-brewed coffees. Lowering the brewing temperature has the potential to enhance cup quality by preventing the over-extraction of undesirable compounds, resulting in a more balanced and refined flavor profile.

The authors performed sensory tests in Rio de Janeiro, Brazil, with specialty coffees roasted to three different degrees (light-medium, medium, and moderately dark), ground to medium grind, and manually brewed over paper filter (Melitta 103, Melitta do Brasil, São Paulo, Brazil) at 10% (100 g powder per liter of water) during 6 min, with spring water at 80 °C (based on Klotz et al. [25]), 86 °C (lowest setting based on the Italian Espresso National Institute guidance of 88 °C ± 2 °C for exit temperature of water from the coffee machine unit [26]), and 93 °C (based on the Specialty Coffee Association guidance [27]). The brews were compared by trained cuppers (n = 5) and by consumer assessors (total n= 515 aged 18–82, average 24 ± 8), using triangle test (ISO 4120:2021 [28]) (under approval number 3.731.774 by Ethics Committee of the Clementino Fraga Filho Hospital, at the Federal University of Rio de Janeiro). For each type of roast, two brewing temperatures were compared (80 °C vs. 93 °C and 86 °C vs. 93 °C). The brews were served at ~ 65 °C. To maintain this serving temperature, coffee in thermos bottles was periodically checked and either mixed with or replaced by warmer coffee when it cooled below 60 °C. Temperatures were monitored to ensure consistent serving conditions across all samples. The ~65 °C serving temperature was chosen because the room temperature was ~24 °C, causing the beverages to cool rapidly, and consumer assessors often complain when beverages are served below 60 °C. Consumer assessors could fill out questionnaires while the beverages were cooled if preferred. The soluble solids content of the brews measured using a pocket refractometer (Atago, Tokyo, Japan) varied between 1.8 and 2.0 °Brix, and the pH was 5.0 for all brews.

The results revealed several challenges. For trained cuppers, coffee brewed at lower temperatures around 80 °C tended to have a higher perception of acidity, which can be desirable for certain coffee profiles, but may be perceived as too sharp or sour by some consumers. Conversely, higher brewing temperatures closer to 93 °C resulted in increased bitterness, especially as samples became darker, due to the extraction or over-extraction of certain compounds, and reducing the temperature helped in minimizing this bitterness, leading to a smoother taste. The perceived body of the coffee, referring to the mouthfeel and weight of the beverage, was also affected; lower temperatures resulted in a thinner perception of body, especially in the lighter roast, which could be perceived as less satisfying (

Table 1. Results from an ISO 4120:2021 triangle test performed in Rio de Janeiro, Brazil, comparing brews from coffees at different roasting degrees and extracted at 93 °C, 86 °C, and 80 °C.

Water Temp. (°C)	Relevant Comments from Cuppers (n = 5) for the Different Brews	No. of Consumer Assessors	Gender (%)	Correct Answers (%)	Preferred Temp. (%)
Light-Medium roast
80 vs. 93	80 °C: Mild taste, less intense, weaker, acidic, less bitter, watery, very different from 93 °C, tea-like, low body, difficult to distinguish the sensory attributes, “died” fast in the mouth, basic coffee. 93 °C: Bitterer, stronger, darker, less acidic, brighter, sweeter, less fruity, burnt, dry, more balanced.	81	Fem 77.8 Male 15.5 Non-b 3.7	44.4	80 °C: 26.7 93 °C: 73.3
86 vs. 93	86 °C: Less bitter, less strong, sweeter and balanced, weaker, milder, medicinal note, similar to 93 °C but short aftertaste. 93 °C: Stronger, more concentrated, less acidic, slightly burnt note, easier to perceive the sensory attributes.	76	Fem 80.3 Male 18.4 Non-b 1.3	35.5	86 °C: 42.1 93 °C:57.9
Medium roast
80 vs. 93	80 °C: Weaker, milder aroma and taste, watery, more acidic, lighter color, lower body, less personality, medicinal note, less complex, basic coffee, flat aroma. Acetic acid, sweet, and salty attributes were perceived after it cooled down. 93 °C: Bitterer, less acidic, more balanced, sweeter, stronger, sharper and more complex, and lasting flavor and aroma, especially the spicy aroma not present at 80 °C, longer-lasting aftertaste.	81	Fem 70.4 Male 28.4 Non-b 1.2	28.4	80 °C: 56.8 93 °C:43.2
86 vs. 93	86 °C: Slightly less bitter, slightly weaker, less powerful, more acidic, acidic aftertaste, very similar to 93 °C, only less complex and short-lasting aftertaste. 93 °C: Bitterer, more intense, slightly stronger, freshly roasted, brighter, sharper, longer-lasting aftertaste.	83	Fem 85.5 Male 13.3 Non-b 1.2	41.5	86 °C: 48.2 93 °C:51.8
Moderately dark roast
80 vs. 93	80 °C: Less bitter, softer, lighter, sweeter, weaker, milder aroma, more watery, weak aroma. 93 °C: Much stronger, bitterer, more striking, more intense, more palatable, more bittersweet, more astringent, slightly sweeter.	109	Fem 83.5 Male 14.7 Non-b 1.8	42.2	80 °C: 62.4 93 °C: 37.6
86 vs. 93	86 °C: Less strong, softer, less bitter, less acidic, fruitier, lighter, sweeter. 93 °C: Bitterer, stronger, sour, darker, astringent.	85	Fem 67.1 Male 31.8 Non-b 1.2	38.8	86 °C: 55.3 93 °C: 44.7

Abbreviations: Temp.: temperature; Non-b: non-binary.

). Achieving the optimal balance between acidity, bitterness, and body proved challenging, highlighting that while lower temperatures can reduce bitterness and avoid over-extraction, they also require careful adjustment to maintain desirable acidity and adequate body.

On the other hand, most of the 515 consumer assessors did not succeed in selecting the different sample among the three-coded cups offered randomly to them, and the reasons why they chose the different brews did not follow a clear pattern. However, as the roast intensity increased, the assessors tended to prefer the samples brewed at lower temperatures (Table 1), which agrees with the results from Klotz et al. [25]. The reported reasons for choosing a brew as different were technically incorrect for most consumers because of the lack of training in defining the differences between bitter, acidic, astringent, and so forth, but they could define strong from mild, preferring the mild ones.

Overall, the results suggest that while lower brewing temperatures can improve certain aspects of coffee quality, such as reducing bitterness, they necessitate fine-tuning brewing parameters to achieve a balanced and pleasing flavor profile for the different types of coffee and roast degrees. Considering the consumer assessor’s preference for lower brewing temperature as roasting intensity increased, that medium and moderately dark roasts are the most consumed worldwide, and that it was difficult even for cuppers to distinguish brews extracted at 86 °C and 93 °C, the potential for lowering the water temperature for coffee extraction in machines is clear. Further research and experimentation are needed to find the ideal temperature that harmonizes all sensory attributes effectively.

4. Recommendations

A concrete, actionable recommendation that balances safety, consumer satisfaction, and health outcomes would be to discontinue machine settings leading to scalding hot coffee (e.g., >90 °C) and to lower serving temperatures in general. Research indicates that very high brewing temperatures can lead to over-extraction of undesirable compounds, resulting in increased bitterness and astringency, which negatively affects the sensory quality of the coffee. By setting a maximum brewing temperature at around 90 °C, coffee producers can avoid these negative taste attributes while still ensuring the beverage is served hot enough to be enjoyable.

Additionally, serving coffee at temperatures lower than the current norm can significantly enhance consumer safety. Studies have shown that beverages served at temperatures above 65 °C pose a risk for esophageal cancer due to thermal injury. By lowering the serving temperature, businesses can reduce this health risk for their customers. The adequate minimum brewing temperature needed to ensure the safety of coffee in terms of microbiological hazards is also 65 °C [6,25].

Combining these adjustments with consumer education is crucial. Informing customers that very hot coffee is not necessarily synonymous with good coffee can shift public perception and preferences. Educational initiatives could include information on the benefits of lower brewing temperatures for flavor enhancement, highlighting how certain aromatic compounds and subtle flavors are better preserved and appreciated at these temperatures.

Implementing these changes positions businesses as leaders in health-conscious practices. It demonstrates a commitment to customer well-being and can enhance the brand’s reputation. Moreover, setting new standards for serving coffee can influence the industry as a whole, encouraging other businesses to adopt similar practices. This industry-wide shift can lead to a new standard for coffee serving temperatures, aligning with both flavor and health research findings, and ultimately benefiting consumers on a larger scale.

5. Conclusions

The evidence linking very hot beverage consumption to increased esophageal squamous cell carcinoma (ESCC) risk has strengthened, highlighting the need to reassess coffee brewing and serving practices. Although this study has shown that assessors prefer coffee brewed at lower temperatures as the roasting degree increases, further investigation is needed into how different temperatures affect the extraction of specific compounds in coffee and their impact on taste and aroma.