Roast Approach: Rwanda Nyamasheke Muhororo Washed - Light Roast

Today's coffee that we are going to approach is the fresh crop (2024/2025) Rwanda Nyamasheke Muhororo washed process.  This coffee arrived in February of 2025 and is the featured coffee in our roasting competition.  Before I get into the roasting, I'd like to mention a few important notes.  While consulting and organizing the roasting competition, I am not serving in any judging capacity.  My goal for sharing these roasts is the same as any other Roast Approach blog post, to help roasters gain a better understanding of how the coffee behaves in the roaster and presents in the cup.  This is by no means prescriptive for how a light roast should be done for the competition.  I hope this provides some insight for roasters as they plan their own approach to this coffee. 

Arrival QC:

• Arrived 02/01/2025
• Moisture 11.3%
• Density 1.13g/ml
• Farm Altitude: 1700-2100 masl 

The Coffee:

This coffee is grown just off the south east corner of Lake Kivu in Nayamasheke region.  The washing station supports 236 local producers, all growing the Red Bourbon variety of Arabica.  The coffee is washed processed and undergoes 12-14 hours of fermentation followed by 12-15 days of slow drying on raised beds.  

The Roaster:

For these roasts, I'll be using a Proaster 1.5 kilo drum roaster hooked up to natural gas.  Batch size is 500g, approximately 40% of roaster capacity.  I've used a small batch size on this roaster to get closer to mimicking the gas power that you might find on a larger production roaster.  It must always be mentioned that each roaster is different.  The type of probe, placement of probe, and batch size will all influence the way in which bean probe temperatures are registered in a roaster.  With that said, don't read too much into the exact temperatures, but look more closely at the theory behind the approach, time spent in different development periods, and rate of rise to get a better idea of how to translate this profile over to your own machine.  I wi

The Goal:

ll be showing three separate roasts.  The first roast will be the control profile that shows behind the roast curves on the second and third roasts.  I hope that this will provide more insight into the changes that were made after cupping the first roast.  I did an initial set of roasts for the coffee to explore the acidity, sweetness and body.  From this set, I took the best roast then worked to improve upon it.  Overall, I was looking for big juicy body, fruit forward sweetness, and complex acidity.  In our initial sample roast cupping for this coffee we noted milk chocolate, lactic acidity, a creamy mouthfeel which coats the mouth, malic acidity, nutmeg spice and fruit notes of stone fruit and tamarind.  In my explorations of roasting this coffee, I found that many of these initial sample roast notes did not match what I was getting in the cup.  You'll see my cupping notes for this coffee veer significantly from our arrival QC cupping.  This coffee is very dynamic and small changes to the roast profile can yield incredibly different results.   

Before I get into theory for how I am roasting these coffees, it's probably good for me to mention that I look at roast profile development in a slightly different way than other roasters.  I like to break a roast down into four key "roast phases," which are defined by the chemical reactions that are happening at that time.  You can read more about this methodology in my blog post here.

Usually I show this graph at the end, but I think it's a good place to start when talking about theory for these roast approaches.  The chart below shows the time spent in each roasting phase (in seconds).  You can see that Roast 1 spent a short period of time developing in caramelization and longer period of time in post crack development.  My goal for roasts 2 and 3 were to extend the pre-crack development by having more time in caramelization and then shortening the post crack development time, shifting sugar development to be earlier in the roast.

Roast 1

The Approach:

In this roast, I started with a high charge temp of 405 F.  Air flow was restricted to 40% (the lowest my roaster can safely pull off) and gas was at 66%.  My plan for this roast was give intense heat during Maillard and pull the heat back as the coffee neared first crack.  Gas was increased to 88% as the coffee hit turn around.  At 260 degrees, gas was increased to 100%.  At 300 degrees, air flow was opened up to 60%.  Gas continued at 100% and airflow was increased to 80% at 340 degrees, while the coffee approached caramelization.  Intense gas application was continued through the initial period of caramlization (beginning around 340) and at 360 gas was pulled back to 88%.  As the coffee approached first crack at 380 degrees, the gas was reduced again to 66% and airflow was increased to 100%.  First crack occurred right around 386.  At 390, gas was reduced again to 44%.  At this point, it was clear that the coffee was on a steady reduction in rate of rise.  This is not a coffee that you can cut the gas and let it coast to the finish.  This coffee will stall out after first crack if you reduce heat too significantly.  It needs some continued push to keep making it through.

The coffee finished with a total roast time of 8:13.  It had a total post crack development time of 1:20 and ended at 402.6 degrees.  Roast weight loss was 13.2%.  

The Cup:

Aroma - Blackberry, brown sugar, vanilla, lime zest, slightly muted aroma (not very intense)

Tasting Notes - Bright and clean acidity.  The acidity is very intense with notes of pomegranate, pie cherry, red currant and tamarinand.  The coffee had notes of pear, raisin, black plum, and currant.  There was a medium body that became increasingly juicy as the coffee cooled.  While the acidity had some complexity, it also had a harshness to it.  

Roast 2

The Approach:

In this roast, my goal was to stretch out the time spent in caramelization (phase shaded in brown) to build sweetness, which I felt was missing in Roast 1.  I was also wanting to reduce the harshness of the acidity in Roast 1, which I felt like may have been due to the amount of time spent in post crack development.  I frequently do light roasts with between 1:20-1:45 minutes spent in post crack development, without getting any harshness or "roasty" notes, however it seemed like it could possibly be too much for what I was trying to achieve with this coffee.  With that in mind, I was also curious as to just how much I could pull the post crack development back without getting vegetal or grassy notes in the cup.  I knew that the coffee still needed to have time for sugar development, so the goal was to shift time from post crack development into caramelization.  Lastly, while Roast 1 didn't show any scorching or tipping, I had concerns that the high start temperature could possibly also be adding to the harshness in the cup.  For this reason, I reduced the start temperature to 390.  In order to compensate for the lower charge temperature, I increased the gas pressure to 100% at 250 degrees, 10 degrees earlier in the roast.

To stretch out the time spent in caramelization, I began reducing the gas pressure earlier, slowly beginning the reduction at 330 degrees to 88%, then reducing to 66% at 350 degrees and lastly reducing to 44% at 375 where it remained for the remainder of the roast.  With this modification, I was able to add 16 seconds on to caramelization.  The roast finished at 397 degrees (5.6 degrees lower than Roast 1) and a total roast time of 8:06 (7 seconds less than Roast 1).  Post crack development time in this roast was :47 (33 seconds less than Roast 1).  Roast loss was 11.3%.

If you are reading these numbers and saying to yourself, "There is no way that you can develop a coffee with 47 seconds of post crack development time", I get it.  When I shared my data with another roaster colleague, their exact response was "You are blowing my mind with these numbers."  The difference in the cup was drastic.

The Cup:

Aroma - Lime, orange blossom, red fruits, sweet ripe raspberry

Tasting Notes - On hot pass, the coffee had a juicy round red grapefruit acidity, full body, and a lactic acidity quality that coated the mouth (like yogurt).  The sweetness brought forward notes of fresh marionberry, raspberry, and black currant.  Combined with the complex body and mouthfeel, there were notes of blackberry yogurt.  As the coffee cooled, a malic acidity came forward bringing flavors of green apple hard candies.

Roast 3

The Approach:

For this final roast, I was curious what would happen if I took a more gentle approach to gas and reduced the end temperature, while trying to maintain time spent in the different phases.  I also wanted to play with what would happen if the coffee had a bit more air flow throughout the roast.  Typically I only change one variable when I'm doing these, but this was going to be my last roast of the day so I threw a bit of caution to the wind.  I'm such a rebel.

In this roast I started with airflow at 50%, instead of 40%.  At 250 degrees I increased air to 60%.  At 340 degrees I increased air to 80%, and finally went to 100% at 375.  This change in air flow resulted in a bit more time spent in drying.  Time spent in the other phases was nearly identical to Roast 2.  This also resulted in the coffee finishing at a lower end temperature of 394 (3 degrees lower than Roast 2).

The overall roast duration was 8:21, 15 seconds more than Roast 2.  These 15 seconds were largely spent in the drying phase.  Roast loss was 11.9%.

The Cup:

Aroma - pink candy, red fruits, plum, orange blossom

Tasting Notes - The biggest difference between this cup and Roast 2 was in the body.  Roast 3 had a lighter and softer body.  The green apple acidity was more present up front on the coffee.  Fruit notes of juicy plum and ripe pear were balanced against the malic acidity.  Soft florals of orange blossom were present in the cup, where they were not in Roast 2.  Overall this cup was very balanced and sweet, but with a lighter and less juicy body than Roast 2.  As the coffee cooled, this roast had more of a honey sweetness while Roast 2 had more of a hard candy sweetness.

Bringing It Home:

My overall takeaways from roasting this coffee was that this is an incredible coffee with so much to unlock.  There was a very wide range of cup profiles that we found from the sample roast and through the various iterations that I produced myself.  While I was nitpicking (as a roaster does) the first roast, it was by all means still a great coffee that I would have been happy to sit and drink.  I cupped the three of these coffees side by side with a set of colleagues in Portland and everyone picked roast 2 or 3 as their favorite.  It was really a matter of personal preference as to if one enjoyed a big bodied juicy cup of coffee or the lighter bodied coffee with soft floral complexity.  

In roasting this coffee, I would keep in mind that it needs some continued gas pressure to avoid crashing out after first crack.  Without any adjustment, it gently reduces in rate of rise on its own.  There is a lot of complexity in this coffee, from the quality of the body to the vibrant acids to the hidden soft florals.  Small changes in the roast of this coffee yielded big changes in the cup profile.  

Happy roasting!