Joanna Joanna Alm, the Swedish roasting champion, gave an interesting talk at the Nordic Roaster Forum 2015. In her presentation ‘Following the Curves’ she presented the most fundamental theories that she build up as a roaster.
This post is a kind of summary of her presentation. You can also watch her complete talk at the end of the post.
Coffee roasting is like developing a picture
Joanna sees coffee as a picture that you can change as a roaster. You can for instance change the contrast, highlight some elements and make it more dark or more bright. Certain shapes of curves have a relationship with negative aspects in the cup. Dullness, bitterness, lacking character are in her opinion all related to the shape of the profile. She also gave some suggestions about how to fix certain things.
Lacking development and nuances: dull
Below you can see a profile that was roasted with a too high charge temperature. Because not enough energy (power/ gas) was added in the beginning of the roast, there was a sharp decline and flattening of the rate of rise later in the roast. This profile resulted in a dull cup.
This dullness could have been fixed by adding more energy in the beginning of the roast.
A coffee that lacks development is like a picture that lacks color and nuances. You can deliberately choose not to develop a coffee fully. You can use this to hide flavours and trying to make a better coffee. You can also use this with a good coffee, but most of it will be roasted away.
Unstructured and unbalanced: bitter
This happens when too much energy is given at the beginning of the roast. This leads to a shorter roast and flatter curve. The rate of rise will not decline that much.
To get some development the roaster has to choose to drop a at higher temperature. This profile will lead to bitterness.
Undeveloped and astringent
An example of this is the classic slow roast. Not much energy is given during the roast. These kind of roasts are lacking warm notes. There are no roast notes, but the character of the coffee does not fully show itself.
Giving lots of energy at the beginning of the roast and flatten the curve in the end too much will result in a developed acidity that has a (negative) spicy character.
- Time: Longer roasts lead a bit to less acidity. Shorter curves may lead to underdevelopment. Not all flavours and sweetness might be there.
- Charge temperature: A too high charge temperature may lead to bitterness. The main reason not to use a too high charge temperature that you want to be able to give enough energy later in the roast
- Heat/ Power
- Airflow: You can roast with fixed airflow or increasing airflow. Both can work. When roasting a short curve she uses less airflow, that will increase the heat in drum faster. Too much airflow can give a bit of dryness.
- Exothermic reactions: When you are going towards crack. High pressure (CO2) in the beans is built up. The beans are expanding. Flat curve after the crack sometimes leads to a more intense cup but it is hard to keep it clean. But when the temperature still rises it seems to lead to a cleaner cup.
Finding the right curve: Have a clear goal
One of the most important things for finding the right curves is to have a clear goal. She always wants the coffee to be clean as possible, acidity at its best and maximum, character as intense as possible, sweet cleanness (not to caramelly) and no roastiness. Joanna advises to do three roasts. After cupping you can see the potential of the coffee. After that adjust your profile to get the best results.
Roasting for Brew Method
A lot of other roasters, roast a bit darker for espresso to mute the acidity and make it easier to extract. Joanna does not roast differently for espresso. She does not want to take away some beauty of the coffee.
After watching her presentation I concluded that the described roast faults can be prevented with Scott Rao’s recommendation for a smoothly (and steadily) declining rate of rise of the bean temperature.
Joanna’s findings confirm Scott Rao’s recommendation to have a smoothly declining rate of rise throughout the roast.
Together with Frans Goddijn, we will look further into a steadily declining Rate of Rise and a development phase stretching up to 25% and a little beyond that of the total roast time, in the little PID controlled fluid bed roaster that Frans uses.
I recommend you to read this post in case you are interested in more information about roast curves and roast faults.
‘Following the Curves’ Roasting Insights from Joanna Alm