Is Cold Brew Less Sour Simply Because It Is Cold?

Cold brew is often described as less sour than coffee brewed with hot water. But comparing a cold cup with a hot one also changes the temperature at which it is consumed. If strength differs too, the effect of brewing method cannot be isolated.

In 2022, Mackenzie E. Batali and colleagues investigated this question by matching beverage strength and serving temperature. They also combined different origins and roast levels to test whether brewing-temperature effects were shared across beans or depended on their characteristics.

Twenty-seven conditions, served at the same strength and temperature

The researchers used three Arabica coffees from El Salvador, Ethiopia, and Sumatra. Each was roasted light, medium, or dark and brewed under three conditions: refrigerated at 4°C, room temperature at 22°C, or with an initial water temperature of 92°C. Three coffees × three roast levels × three temperatures produced 27 conditions. Each was prepared three times, yielding 81 brewed samples for evaluation. This does not mean that 81 people were studied.

Brewing used full immersion, with grounds steeped in water. The ratio was fixed at 100 g of grounds to 500 g of water, and extraction continued until dissolved components approached a plateau. For the 4°C condition, room-temperature water was added before refrigeration for 24–36 hours; the 22°C condition lasted 12–14 hours. Hot brewing began with 92°C water and then continued without further heating at room temperature for 1–2 hours.

After brewing, total dissolved solids, or TDS, were measured, and all samples were diluted with water to 2%. They were then chilled overnight at 4°C and tasted at the same cold temperature regardless of brewing method. This was not simply a comparison of cold coffee with hot coffee.

Seventeen people proceeded to tasting. Of the 14 who completed the full schedule, four were excluded because their repeated ratings were insufficiently consistent, leaving 10 in the final analysis. Assessors trained with terms and reference samples and scored 27 flavor, taste, and mouthfeel attributes. For infection-control reasons, evaluations took place at home, with sample codes and presentation orders controlled.

Even equally cold, cold brew was less sour and bitter

Across roast levels and origins, four attributes showed clear effects of brewing temperature: floral flavor, rubbery flavor, bitterness, and sourness.

Coffee brewed at 4°C was rated more floral than both 22°C and hot-brewed coffee. Bitterness, sourness, and rubbery flavor were stronger in hot-brewed coffee, with no clear difference between the 4°C and 22°C conditions.

Because differences remained after matching serving temperature and TDS, cold brew’s lower sourness cannot be explained solely by drinking it cold. However, brewing times and extraction yields also differed by temperature, so this was not an isolated manipulation of temperature alone. What was established was a comparison of immersion-brewing conditions with these controls in place.

Perceived sourness and measured acidity are not the same

Two measures of chemical acidity showed different patterns. Hot-brewed coffee had lower pH than low-temperature coffee, indicating greater acidity by that measure. Yet titratable acidity, the amount of alkali required to neutralize the coffee to a specified pH, showed no clear brewing-temperature difference for many of the coffees.

Thus, even if hot-brewed coffee tastes more sour, its titratable acidity is not necessarily uniformly higher. Differences in how particular acids contribute to taste and interactions with other sensations, such as bitterness, may influence sourness. The authors also raise the possibility that bitterness and sourness enhance one another.

Testing these mechanisms would require detailed analysis of which acids are present and in what amounts. This study measured pH and titratable acidity, not individual acid composition. The sensory finding that cold brew tastes less sour cannot be translated into a claim that it uniformly contains less acid.

Why might floral flavor be retained?

The authors consider two possible explanations for stronger floral flavor in cold brew. One is the loss of readily volatile aroma compounds during hot brewing. The other is that stronger bitterness and sourness in hot-brewed coffee made floral flavor harder to perceive.

Because volatile compounds were not measured directly, the experiment cannot establish which mechanism operated. The hot brew also stood for 1–2 hours before chilling. Iced coffee rapidly cooled over ice immediately after brewing might retain aromas differently.

Bean-specific characteristics also remained. For example, Ethiopian coffee showed stronger fruity flavor when brewed at 4°C, while dark roasts showed stronger woody flavor at 4°C. Temperature did not produce just one uniform change.

Extraction yield alone is also a poor guide to sourness

Extraction yield describes how much of the original coffee grounds dissolved into the beverage. It differs from TDS, which describes beverage strength. Here, hot brewing extracted more material on average than low-temperature brewing, but subsequent dilution matched beverage TDS. Dilution does not erase differences in what and how much was extracted from the grounds.

The authors highlight that low-temperature brewing produced both lower extraction yield and lower sourness. This ran opposite to the familiar association in hot drip coffee, where lower extraction yields tend to produce greater sourness. They therefore argue that guidelines derived from hot drip brewing cannot simply be applied to immersion brewing across a wide temperature range.

Across the study, roast level affected 20 attributes and origin affected 13, while temperature effects also varied in combination with these factors. The three origin samples differed in postharvest processing too, so these were not purely geographic effects. The authors position the findings as guidance for choosing brewing temperature according to bean and roast characteristics and the desired flavor profile.

This study did not decide which coffee tastes better

The ratings measured how strongly each attribute was perceived. This was not a direct comparison of ordinary consumers’ preferences. The final sample of 10 assessors, incomplete control of home conditions such as lighting, and limited range of beans also need to be considered.

Funding was provided through the Coffee Science Foundation with support from cold-brew equipment manufacturer Toddy, which also supplied brewing equipment. The authors declared no conflicts of interest.

Summary

Even after matching strength and serving temperature, low-temperature immersion-brewed coffee was less sour, bitter, and rubbery than hot-brewed coffee, and the 4°C brew was more floral. However, differences in perceived sourness did not simply match differences in titratable acidity.

The study shows that the brewing process can change flavor even when coldness and strength are matched. Those changes also depend on roast level and bean characteristics. Rather than establishing a single hierarchy between cold and hot brewing, the authors provide evidence for choosing between them according to the flavors one wishes to bring out.

References

Batali, M. E., Lim, L. X., Liang, J., Yeager, S. E., Thompson, A. N., Han, J., Ristenpart, W. D., & Guinard, J.-X. (2022). Sensory Analysis of Full Immersion Coffee: Cold Brew Is More Floral, and Less Bitter, Sour, and Rubbery Than Hot Brew. Foods, 11(16), 2440. DOI: 10.3390/foods11162440 · Full original article.

© 2022 by the authors. CC BY 4.0.