Aug – Sept 2003: Drum Roasting vs. Air Roasting?

Drum Roasting vs. Air Roasting?

Nothing provokes more debate in a roomful of coffee roasters than the assertion that air roasting is as good, and in some cases better than drum roasts. Of course, it’s a hopeless discussion since we are talking about a process where the final arbiter of the result is the papillae of a biased individual (i.e. subjective taste). Taste is not something that can be measured in a lab beaker or by gas spectrometry, or calculated by some formula. Drum roasting has “conventional wisdom” on its side. It makes sense to any cook who simmers their sauces slowly, or faithfully oils their cast iron, that a drum roast will be inherently better. After all, it is slower, transferring heat to the coffee seed by conduction (contact with the hot drum metal) and convection-radiance (warm airs passing through the drum). That’s a perfect blend of stovetop pan cooking and gas oven-cooking techniques. And commercial drum roasters are big, attractive, expensive, old-world-European-looking machines. Home roasters generally look to small shops perhaps thinking that drum roasting is the technique of choice among the cognoscenti. If you are going to spend 8 hours a day roasting in a shop or warehouse, it’s nice to have some good feelings for the machine you use. Air roasting has less intrinsic charm unless you are really into hair dryers. But the roast is easy to observe, the process is “clean” because there is no effluence from atmospheric gas burners, and some variables of the drum process (bean variability and ambient temperature) are less of a factor. In the commercial world of quality-conscious coffee roasters, you are going to see drum roasting as the dominant technique. Only the Sivetz roaster is available for small-scale, quality air roasting. It is a great machine, but consumes a lot of power, is noisy and fire-prone without good maintenance, and has little aesthetic value. It’s a ballsy move to start a new roasting shop with a Sivetz roaster, and not many sensible people (well, ones who don’t want to lose their life savings in a business start-up) will go that route. On the large-scale end of things, factory roasters have a better mix of air and drum roasters installed, but this doesn’t bode well for the reputation of air machines. Big business likes the throughput of air roasting, which boasts roast times as low as 3.5 minutes in huge quantities, continuous roasting (not batch roasting), and less weight loss. The coffee “puffs” a bit more, the appearance is more even and attractive, and the roasts are very repeatable. It’s really big in Europe, with the firm Neuhaus-Neotec providing most of the equipment.

Air vs. Drum Cupping Results
“Okay, Mr. Sweet Maria’s,” I hear you saying. “Enough background blathering … which is better, Drum or Air?” I casually taste the difference between drum and air roasts every single day. We compare HotTop, Alpenrost and Probat versus the air roasters (Hearthware Precision, Freshroast, Caffe Rosto) at different resting periods, as espresso and as french press, all the time. Cupping the results from a specific roaster on our stock of coffees is a combination of expected flavors, and a surprise for me; the formula that x roast method will heighten y quality, but not fully develop z quality is something I can predict, but there is always something in the cup that defies preset notions. By the time a coffee is on our list, I have cupped it as a pre-shipment and
an arrival sample, each time by drum and air roast methods with varying degrees of roast, so you would think this was all rote. But coffee has a way being endlessly counter-intuitive! It’s hard to make a drum vs. air simplification: drum roasters really can’t be spoken of as one thing – as you will see, the
HotTop (perforated drum, radiant heat transfer) cups differently than the commercial Probat (solid drum, conductive and convective heat transfer). Air roasters are more similar to each other in that they all require less time to transfer heat to the coffee charge, but some are more true “fluid-bed” type (Freshroast) while others are hybrid (HWP, Z&D, Rosto). Anyway, I set up two formal, blind cuppings as a basis for the following comments. The first was our Kenya Auction Lot AA Mika, the second was the Brazil Vargem Grande. I chose these to represent the range between wet-processed, bright coffees (Mika) and dry-processed, lower-toned coffees (Vargem). Also, we could evaluate the Vargem as both french press and espresso since it is suited as a straight-roast for both methods. Here are some descriptive results that show how the roast method influenced the cup character: Brazil Vargem Grande –Drum Roast In regular cup testing, the HotTop (17 min..) and the Probat (15 min.) were surprisingly different. The HotTop, with its long radiant heat transfer, was actually fairly bright and light in the top end of the cup, without the development of the deeper tones. The body was good, and the cup was floral and peanuty. The Probat had strongly developed deep flavors of black licorice, black pepper, and bittersweet chocolate. Yes, the HotTop roast was visibly a hair lighter, but not that much. The HotTop was my favorite Vargem cup in this group. As espresso, the aftertaste from the Probat was outstanding in its pungency and chocolatiness. The HotTop was too bright, although the espresso aromas were the best on the table. I liked the Alp. roasts but they were a bit smoky and ashy in this case, so they didn’t score as well as they should have in this cupping.

Brazil Vargem Grande –Air Roast
The Freshroast had a bright and lively cup but lacked the body of the HWP and the Rosto. All had rested for 28 hours after roasting, and the Freshroast (5 min.) body would certainly improve in another day or two. The HWP (7 min.) had a more herbal character than the nutty HotTop roast, but overall I felt this cup was a little dull. Vargem benefits from the longer roast times and the Rosto (9 min.) had the most body of the air roasts, good balance, and aroma, but no notes of interest (herbal, floral, etc.). As espresso, I was surprised that the short Freshroast batch time had such good sweetness in the cup. The HWP had a fresh fruitiness in it that contrasted most with the winey fruit in the Probat roast. This parallels the notion that drum roasts have a more “developed” roast flavor, and risk “overdevelopment” (winier fruit flavors, pungency, smokiness, compression of flavors into the deep end of the cup) if the roast times are too long. Air roasts have a brisk, lively roast taste but risk “underdevelopment” (unripe fruit, gassy or baked flavors).

Kenya Mika –Drum Roast
The bottom end, we’ll call it tenor notes, of the cup were really brought to the forefront in the Probat and Alpenrost, not so much in the HotTop. This is unexpected: you expect longer roasts (HotTop) to taste overdeveloped and push all flavors into the deeper tones, muting the top range. But only in the Probat was the range of flavors deep, tarry creosote-black molasses. This in combination with the aromatic enzymatic notes intrinsic to the Kenya, and blackberry-blackcurrant flavors, leads to a complex though perhaps mismatched cup; like an outfit where the pants are nice, and the shirt is nice, but they don’t exactly go together. This was most true with the Probat roast (a surprise), and less true with the HotTop. In either case, the cup was compressed; the top end was muted, the mid-tones and bass where punched up. This was a Kenya cup for those who like the Sumatra Iskandar or Aceh Gold. Body was good in all cups. Once again, the Alp was a bit ashy and I fear I need to clean it better (the one I use is very old and has quite a lot of buildup in it, which might have unpurified the air in the roaster and “smoked” the coffee). I didn’t score the Alp roasts for this cupping.
Kenya Mika –Air Roast In general these roasts were lively, punchy, with a bouncy and vivid cup character. They put a spotlight on the Kenya cup quality right where it counts (in my opinion), and kept the deeper notes of the cup in better proportion to the top-end notes than the drum roasts. The HWP roasts had good balance and were my favorite. The Rosto had the fruitiness but was a bit flatter overall. The Freshroast was brighter, and the roast taste a bit less sweet and caramelly, so I scored it a little lower. Overall, floral notes were added to the aroma and flavor of the blackberry fruitiness, while the mid-range flavors were sweetened to a light-brown sugar level, not too weighty to interfere with the bright notes. Body was generally .5 to .75 points less than the drum roasts. Cupping Conclusions? Drum vs. air is not black and white, and each can produce great cups in the various brew methods. I wish I could wrap this up into a neat bundle, but I can’t! More than anything, the drum roasts failed to fall into a distinct category and merged with the cup qualities of air roasts to some degree: the Probat was definitely not an air roast, but the HotTop was not so dissimilar as the Rosto and HWP (this revises my impressions of HotTop roast results a bit). I can say this for sure: all roasters produce good cups, and as a general rule (to my taste) the milder, less acidic coffees are best in drum roasts, the bright coffees are optimized in air roasts. In any case, it is always true that you need to put good green coffee into the roaster to have a chance at getting really good cup quality out of it.

Sweet Maria’s Coffee
1455 64th Street, Emeryville CA 94608
email: [email protected]
Sweet Marias Green Coffee Offerings on 8/01/03:
Central American 1 lb 2 lb 5 lb 20 lb
Costa Rican Auction Lot -El Legendario $7.50 $14.25 $33.75 $121.50
Costa Rican Tarrazu – Llano Bonito $4.70 $8.93 $20.45 $72.38
Costa Rican Tres Rios – La Laguna $4.60 $8.74 $20.01 $70.84
Costa Rican – La Magnolia $4.90 $9.31 $21.32 $75.46
Costa Rican La Minita Tarrazu $6.80 $12.92 $30.26 $108.80
Costa Rican Santa Elena “Miel” $4.70 $8.93 $20.45 $72.38
Guatemala Antigua -La Flor del Café $5.10 $9.69 $22.19 $78.54
Guatemala Huehuetenango -El Injerto $4.90 $9.31 $21.32 $75.46
Guatemala Huehuetenango -Huixoc $4.80 $9.12 $20.88 $73.92
Honduras SHG – Selin Recinos $4.90 $9.31 $21.32 $75.46
Honduras Org. SHG – Sebastian Melgar $5.10 $9.69 $22.19 $78.54
Mexican Organic Chiapas $4.60 $8.74 $20.01 $70.84
Mexican Organic Oaxaca -El Olivo $4.60 $8.74 $20.01 $70.84
Nicaragua Org/FT Segovia -Miraflores $4.80 $9.12 $20.88 $73.92
Nicaragua Matagalpa Maragogype $5.20 $9.88 $22.62 $80.08
Nicaragua Matagalpa Pacamara 19+ $4.90 $9.31 $21.32 $75.46
Panama Auction Lot -Elida Estate $6.20 $11.78 $26.97 $95.48
Panama Boquette -Finca La Berlina $5.40 $10.26 $23.49 $83.16
South American 1 lb 2 lb 5 lb 20 lb
Brazil Fazenda Vargem Grande $4.60 $8.74 $20.01 $70.84
Colombian Huila Supremo Lot 4286 $4.40 $8.36 $19.14 $67.76
Colombian Narino -San Lorenzo $5.10 $9.69 $22.19 $78.54
Colombian Organic Mesa de Los Santos $5.10 $9.69 $22.19 $78.54
Peru Org-FT Chanchamayo $5.00 $9.50 $21.75 $77.00
African- Arabian 1 lb 2 lb 5 lb 20 lb
Ethiopian Ghimbi Lot 5025 $4.20 $7.98 $18.27 $64.68
Ethiopian Harar Horse Lot 4338 $5.00 $9.50 $21.75 $77.00
Ethiopian Organic Sidamo Dry-Process $4.50 $8.55 $19.58 $69.30
Ethiopian Yirgacheffe Lot 4452 $5.20 $9.88 $22.62 $80.08
Ethiopian Organic/FT Yirgacheffe $5.50 $10.45 $23.93 $84.70
Kenya AA Auction Lot -Mika 432 $5.70 $10.83 $24.80 $87.78
Kenya AA Auction Lot -Mbwinjeru $5.45 $10.36 $23.71 $83.93
Kenya AA Auction Lot -Rugeju 673 $6.10 $11.59 $26.54 $93.94
Tanzanian Southern Peaberry $4.90 $9.31 $21.32 $75.46
Uganda AA Mbale Bugisu $4.20 $7.98 $18.27 $64.68
Yemen Mokha Ismaili (Hirazi) $7.80 $14.82 $36.27 $124.80
Yemen Mokha Haimi $7.20 $13.68 $33.48 $115.20
Yemen Mokha Mattari $6.55 $12.45 $28.49 $104.80
Zimbabwe AA+ Salimba $4.80 $9.12 $20.88 $73.92
Indonesian- Indian 1 lb 2 lb 5 lb 20 lb
Bali Shinzan Arabica $5.60 $10.64 $24.36 $86.24
Indian Monsooned Malabar Coehlo’s Gold $5.00 $9.50 $21.75 $77.00
Indian Pearl Mountain Peaberry $4.80 $9.12 $20.88 $73.92
Java Government Estate -Blawan $4.70 $8.93 $20.45 $72.38
Papua New Guinea -Organic A $4.80 $9.12 $20.88 $73.92
Sulawesi Toraja Gr. 1 -Lot 1942 $4.50 $8.55 $19.58 $69.30
Sulawesi Aged Kalossi Toraja $6.00 $11.40 $26.10 $92.40
Aged Sumatra Mandheling $5.80 $11.02 $25.23 $89.32
Sumatra Aceh Gold Super-Prep $5.00 $9.50 $21.75 $77.00
Sumatra Iskandar Triple-Pick $5.30 $10.07 $23.06 $81.62
Sumatra Mandheling DP Lot 8809 $4.50 $8.55 $19.58 $69.30
Islands- Blends -Etc. 1 lb 2 lb 5 lb 20 lb
Hawaii Kona-Greenwell Farms ’02 $15.00 $28.80 $69.75 5 lb limit
Hawaii Kona- Kowali Extra Fancy $16.10 $30.91 $74.87 $257.60
SM’s Moka Kadir Blend $5.60 $10.64 $24.36 $86.24
SM’s Espresso Monkey Blend $5.00 $9.50 $21.75 $77.00
SM’s Classic Italian Espresso Blend $4.80 $9.12 $20.88 $73.92
SM’s Decaf Espresso Blend $5.60 $10.64 $24.36 $86.24
SM’s Liquid Amber Espresso Blend $5.30 $10.07 $23.06 $81.62
SM’s French Roast Blend $5.00 $9.50 $21.75 $77.00
SM’s Roasted French Chicory $4.80 $9.12 $20.88 $73.92
Decafs 1 lb 2 lb 5 lb 20 lb
African Highland WP Decaf Blend $5.50 $10.45 $23.93 $84.70
Brazil Prima Qualita WP Decaf $4.60 $8.74 $20.01 $70.84
Colombian Santa Isabella WP Decaf $5.00 $9.50 $21.75 $77.00
Costa Rican Monte Crisol WP Decaf $5.10 $9.69 $22.19 $78.54
Ethiopian Harar Horse WP Decaf $5.50 $10.45 $23.93 $84.70
Ethiopian WP Decaf -Sidamo DP $5.00 $9.50 $21.75 $77.00
Kenya AA WP Decaf $5.50 $10.45 $23.93 $84.70
Mexican Esmeralda Natural Decaf $4.40 $8.36 $19.14 $67.76
Sulawesi Toraja WP Decaf $5.10 $9.69 $22.19 $78.54
Sumatra WP Decaf $5.20 $9.88 $22.62 $80.08
Premium Robustas 1 lb 2 lb 5 lb 20 lb
Uganda Robusta -Nanga Farms $4.00 $7.60 $17.40 5 lb limit

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.