Can the flavour of coffee be predicted by roast curve?

Roast curves are an essential part of a roaster’s experience as perfecting a roast profile is crucial to developing flavour in coffee. Additionally, it is critical for roasters to have a repeatable recipe to ensure consistency across roasts.

Some roasters share their profiles online or with consultants, but some have begun to wonder whether the roast profile on its own actually means anything. For instance, roasters are unlikely to be able to look at a profile and predict a coffee’s flavours or give substantial feedback.

Roast profiles provide a range of information depending on the software used. This often includes, but is not limited to, charge temperature, total roast time, time of event such as colour changes and first crack, rate of rise (RoR), bean temperature, air temperature, drum speed, and the end temperature.

That said, a crucial point to realise is these data points will be relative to the roaster being used. Therefore, comparing roast profiles across roasters may be ineffective as each machine will use different methods to transfer heat.

Discover whether coffee flavour can be predicted by roast curve and the most effective ways for roasters to share profiles.

Coffee flavour: Does it depend on the roaster or the bean?

While many roasters work in the same way, the methods each uses throughout a roast may differ between brands, models, and machine volumes. For instance, a small electric sample roaster might work extremely quickly compared to a larger, 35kg gas roaster.

Bean probes also differ across roasters as some may be more sensitive, providing more noise or disruption on the curves which the software may display differently. First crack may happen at 180°C (356°F) on one roaster.

However, the same coffee may only have first crack at 200°C (392°F) on a different roaster. Furthermore, achieving an agtron of 110 on one roaster might require a 207° end temperature, but 203° on another.

During a roast, between 800 and 1,000 different aroma compounds are developed, which provide unique flavours in the cup. That said, the flavour of a coffee is predetermined by the green bean itself. Therefore, you will be unable to develop a flavour that is not already ‘genetically’ present in the chemical compounds.

For example, it is unlikely that a roaster can take a commercial, low-elevation Brazil and roast it in order for it to taste like a high-grown, competition Panama Gesha. This is because green coffee flavours are determined by several factors, such as variety, soil, altitude and temperature, as well as harvesting and processing methods.

Higher-elevation coffees are more likely to have higher density and complex chemical compounds, leading to a more fruity and acidic cup than a lower-grown and less dense coffee. The moisture content is also an important factor to consider when roasting as this will conduct the heat transfer during the roast.

Discovering the origin of coffee flavour

Morten Munchen from Coffee Mind runs several courses on roasting and sensory skills. Additionally, he has done extensive academic research on the impact of roasting profiles on coffees. Morten’s research delves into which roasting variables have the largest impact on the flavour of coffee.

Notably, the research found that within roasting, 80% of the flavour is impacted by the end colour of the coffee. At least 15% of the coffee flavour is determined by the total time of roast, while the rest of the profile only covers 5% of flavour.

During his professional SCA roasting course, Morten ran tests using triangulation of roast defects with other experienced roasters. He found only 20% of tasters during triangulation could identify roast defects that were determined by the last 5% when the colour and total roast time was matched.

Their research also highlighted the average consumer only noticed significant changes in total roast time and colour changes. Changes in total time of roast by 30 seconds are barely noticeable to professional roasters, let alone the end consumer.

With this in mind, it is unlikely you could predict roast colour from looking at a curve unless you are using a familiar roaster and it is a coffee you have worked with before. Similarly, due to differences in the density and moisture contents of a coffee, it is unlikely you can look at the roast profile and determine whether it is too long or short – unless you have worked with the coffee and equipment before. 

Some may suggest that you are able to identify roast defects by looking at the profile. For instance, a crash or flattening of the RoR may suggest the coffee will be baked and have cereal-like flavours. However, without tasting it, you will be unable to confirm this.

These readings could even be a fault in the connection with the bean probes. Several other roasting defects, such as scorching and tipping, may not present themselves on the curve and will only be noticed in a physical inspection or tasting of the coffee.

Understanding roast curve

The importance of a roast curve lies in understanding the science and heat transfer behind the roasting process, and ultimately tasting coffee to determine if it meets your specifications.

When cupping and testing coffee during profiling, you should use the roast profile combined with your foundation of science to make sense of what you are tasting in the cup.

From here, you can make informed changes to the profile in order to unlock the desired flavours. For instance, if the coffee tastes bitter, shorten the roasting time. If there is scorching on the surface of the bean and a burnt flavour in the cup, reduce the charge temperature or adjust the drum speed.

With so many variables to play with, coffee roasting is unlikely to be a ‘one size fits all’ activity. As a roaster, it is important to build a scientific foundation to understand which flavours are brought out in different parts of the roasts.

Furthermore, roasters must understand how the roast will impact the physical properties of the green beans and the chemical structure. Equally, roasters must develop their sensory skills to be able to confidently taste your coffee and identify what they want to change.

Tasting can help you confidently depict accurate taste notes on your coffee bags. In turn, this helps to further educate your consumers on the intricate flavours of specialty coffees. Custom-printed coffee bags can go a long way in helping your customers understand more about the coffee they are drinking.

MTPak Coffee offers roasters and coffee shops a range of 100% recyclable coffee packaging options that can be custom-printed to your business specifications. Choose from renewable materials such as kraft paper, rice paper, or multilayer LDPE packaging with an environmentally friendly PLA lining.

We use innovative digital printing technology to ensure your custom-printed coffee packaging is a perfect representative of your brand. We offer a quick turnaround time of 40-hours and 24-hour shipping time, and low minimum order quantities (MOQs) to micro-roasters who are looking to remain agile while showcasing a commitment to sustainability.

For more information on customising sustainable coffee packaging, contact our team.