How modern control charts link coffee extraction with consumer preferences and flavour profiles

In the history of coffee preparation, there has long been a simple maxim: there is an ideal zone in which the coffee is neither over- nor under-extracted - a fine line somewhere between bitterness and acidity, between thin and over-concentrated. This ideal zone has been depicted for decades as the centre of the so-called Brewing Control Chart, developed in the 1950s by the Coffee Brewing Institute.

But the sensory reality is far more complex. Coffee flavours cannot be captured in three key words such as ‘weak’, “strong” and ‘bitter’. Consumer preferences do not follow linear axes, but emotional associations, memories and cultural codes. And the variety of possible sensory characteristics far exceeds the idea of a single ideal point.

What is needed is a new navigation tool. A map that not only depicts strength and yield, but also integrates sensory attributes and consumer acceptance. A map that allows the industry to design coffees that are not only technically correct, but also flavourful. This is exactly what the new Coffee Brewing Control Chart has achieved - developed at the UC Davis Coffee Centre through a series of studies with impressive depth and wealth of data.

From the triangular relationship to the sensory map
The classic control chart depicts three central parameters: TDS (brew strength), extraction yield (E) and the brew ratio. When plotted on a two-dimensional coordinate system with diagonal lines, the result is a zone in which coffee is ‘correctly’ extracted. However, this representation recognises no fruitiness, no chocolate notes, no floral peaks. It does not differentiate between flavour and aroma, between sensory intensity and consumer judgement.

The new Control Chart goes much further here: it superimposes a sensory topography over the classic coordinate system - with clearly localised flavours whose intensity can be controlled by their position on the map. At the same time, the map is supplemented by a second layer: consumer preferences, which are visualised on the basis of empirical data from extensive hedonic tests. This creates a three-dimensional space of technology, sensory analysis and market understanding.

Data basis: three studies, one chart
The scientific basis of the new chart is a series of three interlinked studies. In the first, 27 coffees (three TDS levels × three yields × three roasting levels) were evaluated by a trained sensory panel for 30 sensory attributes. In the second study, the influence of the brewing water temperature (87, 90, 93 °C) was analysed at identical TDS and PE levels. In the third study, untrained coffee consumers evaluated the same samples in terms of flavour liking, attribute adequacy and free associations.

The result: over 32,000 individual sensory evaluations, supplemented by 3,000 consumer judgements - a data basis that not only allows sensory attributes to be located statistically, but also their relevance for the market to be evaluated.

Sensory clusters and consumer types
One of the most remarkable findings of the analysis is the existence of different consumer clusters with clear preference patterns. While one segment prefers clear, strong, bitter and roasted flavours, another tends towards milder, fruity and ‘sweeter’ profiles. These clusters can be mapped directly on the menu - as different zones of highest acceptance.

This makes it clear that there is no such thing as the ideal cup, but rather several sensory target areas that appeal to different consumers. What may be a sensory target for a dark roast with a high TDS and high yield may be rejected by other groups as too bitter or over-extracted.

The new chart makes it possible to visualise these differences - and to navigate them in a targeted manner.