What Determines The Color Of The Coffee Extract?

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What Determines The Color Of The Coffee Extract

What Determines The Color Of The Coffee Extract? Before the cup of coffee reaches our lips to take a sip, we have gathered much information about its taste. We smell the aroma – a good indication of the flavours inside, and we can feel the cup’s warmth through the touch of our hands – a good indicator of its temperature. We also see coffee! When we hold a cup of coffee in our hands, we consciously (or subconsciously) evaluate the visual aspects of coffee: its colour, its intensity, its transparency, or its opacity. But what does the visual appearance of coffee tell us, and why is it important?

As colour can be an indicator of the sensory quality of coffee, colour differences can affect consumers’ perception of coffee’s flavour characteristics | Photo: Bluebottlecoffee

We all know that the colour of coffee is essential to consumers. In many studies and standards by the Specialty Coffee Association (SCA), roast level — a quality measure, often expressed by colour (light, medium, or dark) — is the determining factor most decisive influence on consumer decisions.

Recently, experimental studies by Qian Janice Wang at SCA have demonstrated that, even for experienced cuppers, the colour of the coffee affects their judgment. about the coffee itself (they found differences in the flavour of identical coffees by indirectly changing the coffee’s appearance). This suggests that the visual colouration of coffee can influence other sensory perceptions of coffee at the neural level, a phenomenon the researchers call the “multisensory effect.” or cross-modal effects.

What does the colour of a coffee drink tell us?

From the perspective of Sensory Science, the correlation between colour and taste is one of the most studied. We tend to associate specific colours with specific tastes: for example, red/pink is often associated with sweetness, green with acidity, and black with bitterness (so we don’t have to worry about it) just tend to look for foods and drinks that are red to make them sweeter). The colour of coffee (drink) gives us insights into the chemical composition of the drink itself and gives us valuable clues about what flavour we can expect. Dark black coffee can be bitter and robust, and russet coffee can be tea-like and pale. Users with knowledge of chemistry can give some simple explanations; for example, Melanoidin– is a group of dark-coloured compounds formed during roasting. These browning compounds affect flavour and aroma in foods and are the main reason why the famous “Maillard reaction” produces both the brown colour and delicious taste in foods.

Melanoidin is formed when sugars and amino acids combine (via the Maillard reaction), which is a major contributor to both the color and flavor of coffee, so it is the reason for the changes in color. Coffee will lead to a difference in coffee taste.

Wikipedia

But what makes the colour of coffee? In 2021, researchers at UC Davis Coffee Center, conducting a study evaluating the chemical differences between hot and cold brewing, noticed a finding: the same coffee, brewed with the same amount of dissolved solids (TDS) but using different water temperatures, actually looks different. This stimulates many scientists to search for answers to why coffees that are precisely the same apart from brewing temperature can look so different. Experimental results lead to a fantastic discovery: The colour of brewed coffee is influenced not only by its extraction composition and strength but also by the brewing temperature, to the extent that one can predict brewing temperature by the visual colour of the coffee get high.

Accurate colour images, using natural white balance, of six coffee extracts in a 5ml glass jar. Samples are annotated origin, roast degree, and brewing temperature | Photo was taken from research by Sara E. Yeager

Despite the fact that the color of coffee – from roasting to brewing – is an important indicator of roasting level and quality across the industry, our understanding (and measurement) of color mostly subjective.

sca.coffee

What determines the colour of coffee after brewing?

Quantitatively, the colour of coffee beans after roasting can be measured using the Agtron Gourmet or Commercial Scales. But often, these quantitative measurements are pretty expensive and not very common, so they will be supplemented or replaced by more relative determinations of roast colour, such as “bright”, “medium”, or “dark”. On the consumer side, colour is often the first measure of consumer-created quality, making it an essential indicator of sensory quality. In addition, product-specific colour changes – such as browning that occurs during coffee roasting – serve as markers for certain “thresholds” in changes in smell and taste. of coffee. Therefore,

When it comes to coffee-based beverages, colour is mainly measured subjectively. We do not place great emphasis on determining the colour of the coffee extract, simply on how the colour of each coffee tends to vary from sample to sample and the differences in How colour affects consumers’ perception of their drinks.

In the experiment we cited at the end of the article, scientists measured the colour of coffee brewed with a Toddy pot from several sources: El Salvador – Honey (ELS), Ethiopia Guji – Washed (ETH), and Sumatra – Wet hulled (SUM). Three times the phrase is homogenized to a more extensive set of samples; this homogenizer is diluted to TDS = 2% for colour analysis of the absorbance spectrophotometer and Agtron Gourmet colour scale. The procedure was performed in triplicate for each sample type, for 3 coffees × 3 roast levels × 3 brew temperatures × 3 test replicates = 81 sample sets (including 243 individual brews, identical to a triple). Samples were stored in the refrigerator for approximately 48 hours until colourimetric analysis.

Experiments have shown that the colour of coffee extracts is strongly influenced by the degree of roasting and the brewing temperature, especially in light or medium roasts. Intuitively, this is quite understandable, as increased roasting will make the beans darker, leading to a darker-coloured extract. It’s worth noting that using a “cold” brewing temperature (4 or 22°C) results in a drink that is much redder than the typical dark brown colour of hot brew (92°C). In other words, the colour of the coffee grounds is not transferred directly to the brew, and the brew’s colour will change significantly based on the temperature and origin of the brew, which complicates coffee selection. and extraction parameters to achieve the desired shade of brewed coffee. This is an abandoned area of ​​research, unexplored even with the recent rise in the popularity of cold brew.

Accurate colour images, using natural white balance, of six coffee extracts in a 5ml glass jar. Samples are annotated origin, roast degree, and brewing temperature | Photo was taken from research by Sara E. Yeager

The color of a coffee beverage can profoundly affect sensory characteristics. Drinks with red color may be less bitter and sweeter than drinks with darker red color.

Johnson & Clydesdale ,  1982; Ja Maga , 1974

So, what are we going to do with the coffee colour?

Although it is still unclear precisely what causes the difference in colour between different coffee extracts at different roasting levels and brewing temperatures. Although we know that the brown colour in roasted coffee results from Melanoidin produced during roasting and the caramelization of sucrose (Bradbury, 2001; Illy & Viani, 1995; Macrae, 1985). The MelanoidinsThese can be very different in composition, type and depending on the degree of roasting. Melanoidin is a macromolecular product of the Maillard reaction and can be divided into three categories based on its molecular weight: low, medium and high (Bekedam et al., 2008). The amount of each type of melanoidin varies according to the degree of roasting; The darker the roast, the more significant the proportion of high molecular weight Melanoidin (Bekedam et al., 2008). An increased concentration of high molecular weight Melanoidin can lead to a darker colour of dark roasted coffee.

The fact is that the colour of the coffee grounds/powder is not transferred directly into the extract and the brew’s colour will change dramatically based on the temperature of the brewing water.

Melanoidins are generally defined as brown, nitrogen-containing macromolecular compounds that absorb light at 405-420 nm. Their chemical structure is extremely complex and largely unknown due to the fact that so many components in green coffee beans play a role in their formation.

Bekedam et al. (2008)

Likewise, Brown Pigment also comes from the caramelization of sucrose, which occurs whenever the roasting temperature reaches above 130°C (Trugo, 1985). The resulting product is a water-soluble heterocyclic compound that can then polymerize to form Maillard-like brown pigments (Tressl et al., 1998; Bradbury, 2001). Including two different colour compounds (melanoidin and caramel) suggests different extractability at different brewing temperatures. The size and solubility of these compounds will affect their overall extraction and lead to a change in the colour of the drink.

The bottom line is that both roasting degree and brewing temperature affect the colour of the coffee beverage. Still, the colour of the coffee extract doesn’t always indicate the colour of the beans or the authentic flavour of what it will be like. Cold brew coffee, brewed at room or refrigerator temperature, will have a redder colour than the typical black-brown colour of hot coffee. When extending the inference, roasting levels and brewing temperatures can be deliberately chosen to obtain the desired coffee colour, providing new branding and marketing opportunities.

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Reference source

[*] This post shares the findings of a recently published paper, “Roast level and brew temperature significantly affect the colour of brewed coffee.” colour of coffee drinks”, published in Food Science & Technology.

  • Yeager, SE, Batali, ME, Lim, LX, Liang, J., Han, J., Thompson, AN, Guinard, J.-X., & Ristenpart, WD (2022). Roast level and brew temperature significantly affect the colour of brewed coffee. J Food Sci, 87, 1837–1850.  https://doi.org/10.1111/1750-3841.16089
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