Modern Roasting: Roast Times

by | Jul 23, 2015 | 1 comment

It has been a while since I took the time to write an article, but a lot has happened and many experiences gained in the past year.  One of the biggest advancements in modern roasting techniques is that of roasting times.  I am particularly referring to a recent Cropster article showcasing some of the winning roast profiles of the 2015 World Coffee Roasting Competition (WCRC) held in Gotenburg, Sweden.

First, may I say: All hail Audun Sørbotten from Audun Coffee in Norway for being crowned World Coffee Roasting Champion 2015!

Data logging is important

The data that Cropster shared here is invaluable.  Us roasters are often very secretive about our roasting profiles, but this is an excellent opportunity to see what the very latest trends in roast profiling and development are. Using Cropster’s latest version of their award winning software, the competitors were able to track not only temperatures and the infamous Rate-of-Rise (RoR) curves, but they can also now log gas pressure settings and air flow measurements. These metrics have opened up the previously dark art known of coffee roasting and brought it into the 21st century of Twars and Selfies.


Rate-of Rise, or RoR in short, has been described by many to be a game changing metric that has allowed roasters insight into their temperatures profiles that has never before been possible. Sometimes called DeltaT, RoR is simply a mathematical first order derivative (that was drilled into me in 4th year Analytics by professor Spoelstra.  I failed. 3 times.  Took me 2 years. Yeah) that is applied to any curve. In roasting’s case, it’s almost like amplifying the temperature curve by 100 times, looking at how quickly changes are being affected into the beans instead of just seeing what the effect was. This gives the operator valuable insight into what is happening at every second during the roast.  With RoR, the operator can be proactive instead of merely reactive, where being reactive often lags several seconds or even minutes behind the actual event that caused the initial change in behaviour of the roasting profile (for example endo/exothermic stages, first crack, drying phase etc.).

For a full explanation of Rate of Rise, be sure to read Cropster’s article on it.  Also watch this space for Genio’s own spin on RoR in our latest generation machines.

WCRC Profiles

Here are a few of the roast profiles that Cropster’s article shows. Now, bear in mind that these profiles are catered for the World Championships standards that are aimed at showcasing incredible coffees and not necessarily tailored for the conservative palette. They are certainly more geared towards the Norwegian and modern European style of light roasting, but they are World Champions nevertheless and I think that all roasters and roasting styles can learn from them.  For example, the South African roasting environment will never roast such light and bright coffees as our market and palettes will not accept this style of roasting…yet.

Images courtesy of Cropster

Images courtesy of Cropster

Roasting times

In the above profiles the one thing that is clearly evident is the short roasting times.  Keep in mind that these roasts were done on a 1kg machine, which might account for faster roasting times as it may be more difficult to get the same kind of energy into larger roast batches. On our Genio’s we can comfortably do this by using 4kg batch sizes in our 6kg machines, while full 6kg batches will take somewhat longer. Hey, not even a Ferrari can go around the track with two fat blokes in the front seats in the same time as “The Stig” can do alone in the car! But the two fat blokes can still drive to the pub in record time, just like your Genio 6 full batch roasts can still be completed in an excellent time, but needs some weight-shedding before attempting Stig-like profiles.

The longest roast in the WCRC2015 winning profiles was 9:58 and the shortest 7:28. This is extremely short roasting times in South African terms and very few of our roasters will roast this fast. Most of our roasters still aim for 15 minutes, and very, very few have any form of logging to actually see what is happening in their roast profiles. At these roasting times, more of the sugars are retained in the beans; shorter roasting = less caramelization and more sugars and sweetness with lower body. Longer roasting = more caramelization and less sugars, acidity and brightness with fuller body. So these roast masters (roast MASTERS, I do not believe that anyone and everyone who roasts can take on that title) are clearly aiming at retaining the unique sugars and sweet characteristics that makes their coffees stand out amongst the rest.  The modern way of roasting sees anything over 15min as baking the beans, although there will always be exceptions.  Roasting is a progressive, fast process of intense chemical reactions, where as baking is, well, baking.


Shorter roasting times are not all about dropping the coffee out sooner. You have to consider bean development. As Scott Rao’s The Coffee Roasters’ Companion book preaches, bean development is where the true flavour in the bean is developed. An underdeveloped roast will have that horrible sourness to it that so many tries to pawn off as sweetness. There are only so many ways to try and trick people into believing that you are roasting sweet coffees before someone will stand up and say “This isn’t sweet. It’s sour. Gimme back my money” (Underdeveloped roasts are a little pet peeve of mine).  Looks for descriptors like “lemony acidity” and (my favourite) “citrus burst”.  Instead, a true roast master would ensure that their beans are properly developed and not try to dupe his/her customers into believing that sour is cool.  It isn’t.  Stop it.

Bean Development

As stated before, bean development is where the novices are separated from the pro’s. It is a pity that all of the WCRC competitors did not press the First Crack button on Cropster that starts the Development timer, but we can extrapolate from the RoR curves that the winner, Audun Sørbotten’s development times were around 12-14% for his Single Origin and Blend roasts. Now this is not long by any stretch, but at least there was some development time which will ensure that his beans are properly roasted through both the inner and outer bean sections. Again, these profiles are not for the conservative roll-out-of-bed coffee drinkers.  Without development time (Scott Rao suggests 20-25%), the beans are essentially still green on the inside, leaving those nasty, acidic and acrid sugars untouched and causing the unpleasant sourness that sends so many of our customers back to the instant coffee dark ages.

Wait… “extrapolate from the RoR curves” where the first crack was?  Yes, we can! We know that First Crack is a physical breaking of the bean along the centre line as a result from pressures that built up inside the bean. The pressures are essentially steam pockets that form from the gasses being created inside the bean. When the pressure buildup becomes too much, the bean cracks and releases all of this stored up energy. We can see this in the RoR curve where a sharp change is registered, especially in the Environment RoR curve.  Although the exothermic stage begins a short while before 1st crack (it is a common misconception that it begins AT first crack), we can still clearly see the effect that this stage has on the roast profiles, especially i.t.o. RoR.

Does it have to be 20-25% ?

No, your development times certainly do not have to be within those parameters.  Scott Rao suggested that the best coffees he has ever tasted and remembered for years thereafter all had a 20-25% development time in common.  However, I strongly doubt if any of those coffees were your run-of-the-mill Brazil Santos or Columbian Excelso beans that many of us roasters rely on for our bread and butter.  All profiles cannot be painted with the same brush here.  Your development times should be carefully crafted through cupping.  You wouldn’t believe it, but I can count the roasters who actually taste their coffee after roasting it on one hand.  Very few ever do, leaving them to believe that a single sentence in a single book decides the outcomes of all roasting profiles from here to eternity.  No, CUP your coffee to determine the best development times, and make sure you log your data using a proper system so that you have enough data on hand to make calculated decisions about your main form of income.

The Lesson

The lesson for today is that the roasting world is an organic, constantly evolving world.  The roasting times of the 80’s and 90’s that easily peaks 15 and 16 minutes (often even longer) is over.  Our coffees, equipment and understanding of roasting has long surpassed this era.  Roasters need to be on top of their game and make sure that their roasting profiles, even something as simple as the overall roasting times, are carefully monitored and logged. This should of course be in accordance with what your customers are looking for. And NO, saying “but my customers have always loved our coffee” is not good enough. When your now loyal yet mature (read ancient) customers disappear (and they will), you will have lost the new generation of beard-wielding hipsters and annoying youngsters who have now grown into your potential customers because you refused to listen to them whine about your bitter, burnt, outdated product.

Shorter roast profiles may not be in style in all circles yet, but so too was Facebook not 4 years ago. I bet your parents have tweeted/whatsapped/poked you in the last year. Admit it. They have!

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1 Comment

  1. John

    Great article. Some of my early roasts were in the fast light category and produced an incredible cup full of flavour and sweetness. Unfortunately most customers who tried it liked the coffee but preferred something a lot darker (stronger). I guess we have a long way to go still in educating our customers on the benefits of light roasts.

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