How time and temperature become interchangeable in full immersion brewing – and what this means for product development, sensory design and the future of coffee processing

Cold brew has long been seen as a world apart — a slow, smooth, low-acid alternative to the hot brew rituals of baristas and cafés. Over the past decade, it has transformed from a niche curiosity into a major commercial category. But while its rise has been rapid, our understanding of why cold brew tastes different — and how those differences arise — has been surprisingly shallow.

Until now.

New scientific research on full immersion brewing suggests that the defining differences between cold and hot brewed coffee may not be rooted in chemistry alone — but in the interaction of just two variables: time and temperature. And under certain controlled conditions, these variables can substitute for one another. In other words, a long, cold extraction can yield a nearly identical flavour profile to a short, hot one.

This insight has profound implications for sensory design, product development and quality control in both artisan and industrial contexts.

The experiment that changed the equation
At the heart of this new understanding lies a comprehensive comparative study of full immersion brews at three temperatures: 4 °C (cold brew), 22 °C (room temperature) and 92 °C (hot brew). For each temperature, five time points were selected, ranging from rapid extractions to 24-hour steeping periods. All brews used the same coffee, grind size, and brew ratio.

The resulting 30 brews were then rigorously analysed — not only in terms of Total Dissolved Solids (TDS), extraction yield, pH and titratable acidity, but also through trained descriptive sensory evaluation.

What the researchers found was remarkable: certain long-time cold brews (e.g., 24 hours at 4 °C) produced flavour profiles almost indistinguishable from short-time hot brews (e.g., 4 to 10 minutes at 92 °C). Bitterness, fruitiness, acidity, body — all could be matched across radically different extraction conditions.

This suggests that the defining characteristics of a coffee cup are not exclusive to hot or cold extraction — but depend on achieving a particular balance of solubles through controllable process parameters.

Sensory convergence, chemical divergence
While sensory similarity can be achieved, the underlying chemistry still shows differences. Hot brews reach equilibrium TDS values much more rapidly. Cold brews continue extracting gradually over time, with a slower rise in both acidity and perceived strength. The pH remains slightly higher in cold brews, but the titratable acidity — which correlates more closely with perceived sourness — still increases over time.

These subtle chemical differences, however, do not always manifest as perceivable sensory distinctions. In practice, the sensory balance — the proportion of sweet, sour, bitter and aromatic elements — can be engineered across both methods.

The implication? Cold brew is not a fundamentally different beverage. It is a different path to the same sensory destination.