Hello everyone.

Upon receiving my new roaster as a gift (which was a huge surprise by the way) I started experimenting right away with the coffees I had (this is my first dedicated roasting equipment). I have to say that I am very happy with the QUEST M3 roaster and more convinced today that it's more appropriate to my approach into roasting (my specific needs) than the other offerings available. Having a dedicated roaster has also made me revisit all my previous views on roasting, and revisit my former opinions on what I would like and would not like in the taste of the final drink. After some time of roasting and tasting using the new roaster (which I have been doing 80 grams at a time -a disgrace for a half-pound roaster) I realised that there has been one predominant defect in the final product that was so overwhelming that every other defect was minor compared to it, that being the acrid acidity I later discovered is attributed to a number of substances collectively called the "chlorogenic acids" (which as I understood aren't one substance but rather a number of substances that are collectively called as such). In the previous years, I used to roast coffees that are not particularly acidic or particularly hard to roast (mostly Ethiopian and Yemeni coffees), and so I did not have to worry much about the acidity. However, once I started roasting some really-large, Mexican and Nicaraguan beans that I bought from a local roaster this summer I realised that I was absolutely hopeless confronting a very clear, acrid acidity that insisted on appearing in every cup. This taste was so unpleasant in my opinion that I felt was my single and foremost enemy if I wanted to be a good home roaster. I went through some reading in this website and read about the "chlorine pool" tastes and that they were to be handled in the later part of the roast (since the substances responsible of them were supposedly "stable" at the lower temperatures). So I started a series of experiments by following the general guidelines in roasting except for one variable, that being the ultimate temperature (which I stuck at for 4 minutes at the end of the roast for all of the experimental roasts). The total roasting time was around 14 minutes for all the roasts whereas the ultimate (final) temperature was selected from the following set: 210C (410F), 215C (419F), 217C (422F), and 220C (428F). In the case of the lowest of these temperatures (i.e. 210C) the acidity was there and was strong enough for me to consider the espresso undrinkable, and so in the other case of 215C. As for the 220C case, the final roast smelled and tasted like the burnt oils I usually smell and taste in the darker roasts, which is an observation supported by the droplets of dark yellow water I saw within the roaster (the M3 roaster has a path for air circulation which allows the moisture within the circulated air to condense in some spots within the roaster). Upon wiping these yellow droplets with a tissue I noticed that it turns out black in colour and smells somewhat like tar (as if I knew how tar smells like), therefore I concluded that some transformations start to happen at this temperature that I did not like them to happen. Note that by comparing the droplets in this case to the ones I could witness in the 215C case, the droplets in the latter case were transparent and smelled only grassy with no evident trace of burnt oil. This made me go for an ultimate temperature between 220C and 215C, which was 217C. This final trial turned out to be the best of all trials but had some problems as well. First of all, though the acrid acidity was not evident, there was still some acidity that is not as offensive (which I would describe as acidity rather than only brightness). Second, there has been a hint of the burnt-oil tastes that were evident in the 220C case. Therefore, I concluded that getting deeper in the roast was not the best solution for handling this defect, as it seems that someone will have to go for a compromise between the burnt-oil flavour and the intensity of the acrid acidity, which in this case turns out to be a delicate compromise (as in 217C compared to either 215C or 220C). Furthermore, in all the experiments, the acidity was still overwhelming when I do hot extracts (that being the "second" shot on the La Pavoni Professional). This means that the 217C roast was only good when extracted as a first shot (using low extraction temperatures) but not as a second shot (I do not know the actual brew water temperatures). In the case of a hot extractions the acidity was still overwhelming in all the roasts including the one with an ultimate temperature of 220C.

Therefore, I started looking for a better and a more reliable solution, and while doing so I tried to re-roast beans to certain temperatures for certain times using my modified pop-corn popper (as to test the stability of the substances responsible of the acidity at those temperatures). I tried temperatures such as 170 and 180 Celsius for periods up to ten minutes but had no success. The acidity remained with no noticeable change in intensity, which supported the belief I had that the substances responsible of the acidity were stable at those temperatures (which turned out not to be exactly the case).

Later on I did some reading and came across this paragraph in a lengthy book on coffee flavour (which I do not pretend to be able to understand any reasonable proportion of it), namely in a section on "cholorogenic acids":
"... For a Brazil arabica, the authors found a maximum for 3- and 4-CQA (i.e. types of chlorogenic acids) after 40 minutes at 177 degrees Celsius (350 F), and after 45 minutes at 205 degrees Celsius (400 F) the total CGA content is only 1.1% (compared to 6.7% in green coffee)."

(Another paragraph that may also be of interest in this context: "Clifford's group found that for 5-CQA, the most abundant of all, a taste threshold of 50 ppm (parts per million) in distilled water is a bitter recognition threshold. At 500 ppm a metallic note appears, and at 1g/L (1000 ppm) sourness and other notes appear. More limited studies on 3-CQA give a bitter threshold similar to that of 5-CQA.")

I know that it seems like a chemical experiment rather than an actual roasting experiment but I actually tried it. I tried to proceed in the roast as usual with the little (or rather BIG) twist of hanging at 177 degrees Celsius for 35 whole minutes (which I thought was close enough to 40 minutes to give a reasonable indication of the effect of this method on the acidity I was experiencing), then I ramped to an ultimate temperature of only 213C before ending the roast (which in the usual case would have lead into some intense acidity). The minor surprise was that the coffee did not pop at all (the first crack usually "ends" at 213C) whereas the major surprise was that the coffee was lacking the clear acidity completely, even when extracted hot (as a second shot with a reasonable wait between the two shots). There has not been any perceivable acidity compared to the previous trials. However, the taste was different, somewhat very similar to an Italian coffee blend from "Felicori", which I may refer to in this context as a reference because I come from a totally different place (in brief, there is a very long and strong aftertaste that is either chocolatey or nutty, which is not necessarily pleasant but is not as offensive in my opinion as the acidity -not as awakening of the senses as the acidity but is subtle). Of course, I do not advise people to have such an unbelievably-long roast and I do not claim that all the effects coming along with such a technique will be favourable, but I am confirming that the technique can actually succeed in eliminating the offensive acidity. Note that I turned the airflow off completely for the whole 35 minutes I spent at 177C, while in the same time using the circulation path provided by the M3 roaster (funnels closed). This means that the moisture released from the roasting process was preserved throughout this time within the rotating drum. This moisture may have played a role decomposing the "chlorogenic acids" into simpler acids that were then transformed into other substances that are not acids anymore (I am not very good in chemistry . For the simpler acids that the chlorogenic acids could hydrolyse into look up "Quinic acid" and "Caffeic acid" in Wikipedia. For the other chemical compounds these simpler acids may turn into I think they are called lactones).

I do not pretend that to be a chemist, but given that I read something, interpreted it somehow (wrongly perhaps), and translated it into an experiment that had an interesting outcome is what I am sharing here. Please do not hesitate to correct, clarify, explain, add, etc.

NOTE:
I noticed that resting can have a good effect on reducing the intensity of some of the unpleasant tastes in roasted coffee beans (perhaps including the acidity). However, I hypothesised that resting can help obscuring some of defects in roasted beans (using simple mechanisms such as evaporation, decomposition, etc.). That is, I assumed that a good roast can benefit from resting but should not rely on it to get rid of some of the unpleasant tastes. This is not necessarily true but I relied on it as an "implicit truth" in these experiment which meant that I would only allow the beans to cool for around 30 minutes before making an espresso to evaluate the roast. Note that this also applies to the final, 46-minute-long roast, which lacked acidity right after roasting with no rest.

You are doing interesting work; but you might consider editing your posts to separate what you did and tasted in each roast, from what happened in subsequent roasts, or from the interpretation. I'm getting old and senile, and find it hard to keep all this straight without some road signs.

What coffees did you roast? How long, and to what temperature? How did they taste? These, one roast at a time, are the facts. The experimental results on chlorogenic acids are an interpretation on why you are getting these results.

Clearly, you prefer light roasts; and you are absolutely right that excessive grassiness and acidity are the bane of light roasts. The conventional wisdom on this is
-- that you need to be up around 390F before you can roast out the acids. Above this temperature, the acids break down.
-- Prior to that, between 300F and 390F, the acids remain and the sugars and amino acids are turned into nutty, woody and malty tasting Maillard reaction compounds. A fast ramp through this zone to the first crack preserves some sugars from this reaction and can balance the acidity.
-- lowering the amount of water in the bean by drying he coffee longer, from 200F to 300F, will speed the breakdown of acids, and produce lighter roasts without grassiness. However, drying too long changes the roast chemistry for the worse, aromatic compounds do not form, the roast will taste flat and slightly charred.

I'm not exactly sure what you did; but perhaps slowing down below 300F and speeding up from 300F to 390F can help.

I tried to be systematic, so I did not mix coffees. All of the above experimenting has been done using a single Mexican coffee (a one I bought from a local roaster that I know nothing about beyond being Mexican). At the beginning, I performed a set of 4 roasting experiments, each using 80 grams of green beans (weighed using a digital scale). In these four roasts I followed all of your roasting guidelines. That is, I would heat up the beans at the beginning for exactly four to five minutes at the end of which the beans will be crossing the 300 Fahrenheit point (147 Celsius) with a uniform yellow appearance. Then they will proceed as fast as possible to first crack using maximum element power but low fan speed. Then slightly prior to first crack I would discharge the heat stored in the drum by lowering the element power and temporarily using high airflow. This drives the beans right to the beginning of first crack but most importantly allows me to slow down the ramp significantly after the 400 degrees Fahrenheit point (205 Celsius). After this point I can ramp very slowly to desired ultimate temperature and stay there for around four minutes. This in brief describes how I carried out these four roasts. I was very consistent in the way I roasted them, everything was exactly the same except for the ultimate temperature. The objective was to test only the effect of the ultimate temperature on the sourness I was experiencing with this bean. The results were not ideal like I said. Sourness was still dominating the cup flavour on the second shot (hot extraction on the Pavoni). My interpretation for this is that even though some of the substances responsible of the sourness were roasted out, some other substances that needed higher brewing temperatures were still there.

Then I did some insignificant experimenting with the modified pop-corn popper, and finally did the 46-minute roast (in which I stayed at 177C for 35 minutes). I did not experience grassiness throughout my experiments. This roast has been carried out using the same coffee/batch size and while following the same guidelines above, except for the detail of getting stuck at 177C for 35 minutes. This increased the roasting time from 14 minutes to around 46 minutes.

I am aware that the chemical interpretations are far from being factual information, but there has been a number of reasons that made me include these speculations and quotes, amongst them are the definite statements I read in Wikipedia and other places about the perceived sourness in coffee being attributed to these chemical compounds (and about there being a correlation between sensory assessment of this quality and analytic quantities of those substances). My goal was to verify whether it was really the case that this sourness needed such a high roasting temperature (above 390F) to be roasted out or not (which was something I was not willing to do given the other burnt-oil flavours I would run at the risk of developing as I raise the temperature to get rid of the sourness). This required that I investigate some of the candidate substances behind the sourness, which is unverified I admit. However, as we move to the facts: I failed in eliminating the acidity by going to higher temperatures (up to 220C), whereas I succeeded using a totally different approach. This was an interesting fact. The resulting beans from the 46-minute roast were not acidic even when brewed with a hot group (hot extraction). My interpretation for this observation is that the sour substances that existed in all of the four former roasts were roasted out in this final roast.

Ethiopia is so much closer to you.

Hello Orwa, and congratulations on your new roaster!

orwa wrote:.................... I would only allow the beans to cool for around 30 minutes before making an espresso to evaluate the roast. ........

I think this 30 minute post roast is a big problem for espresso. As well, the aroma development is much better at 12-24 hours rest. Too fresh, the excess CO2 content causes extraction problems for espresso. If you are grinding for espresso at less than 2-3 days rest then try letting the grind 'exhale' for 30 minutes to 1 hour rest before pulling the shot. Give your espresso roasts a chance by sampling them at days 3-10 rest. Try to limit exposure to O2 during the rest period.

Have you been able to sample this same Mexican bean roasted at your local roaster?

FWIW, in most drum roasters the 'bean temp' thermocouple is positioned fairly high in the drum - with the result that when roasting a very small load the beans will not touch the tc, so the temperature shown is measuring the air temp in the drum rather than the bean temperature.

Regards, Henry

Frost wrote:Hello Orwa, and congratulations on your new roaster!

I think this 30 minute post roast is a big problem for espresso. As well, the aroma development is much better at 12-24 hours rest. Too fresh, the excess CO2 content causes extraction problems for espresso. If you are grinding for espresso at less than 2-3 days rest then try letting the grind 'exhale' for 30 minutes to 1 hour rest before pulling the shot. Give your espresso roasts a chance by sampling them at days 3-10 rest. Try to limit exposure to O2 during the rest period.

Have you been able to sample this same Mexican bean roasted at your local roaster?

I have had many problems in the past caused by insufficient resting of coffee beans (or equally by undesirable properties in freshly-roasted beans that would diminish in a two-day or three-day rest). I did not only dislike the taste but also did not like how the results looked like: the pour was too thick, the grind had to be coarser than usual and the crema was bubbly and non-lasting. Nevertheless, I did not think that resting of roasted coffee beans was a good idea in the case of these experiments because it would only make it harder to interpret the results and to correlate them to differences in the roasting profile. Furthermore, I noticed that the roasts described here did not have some of the qualities of freshly-roasted beans I had experienced, namely the pour was not as thick, there was no need to use a coarser setting for the grind and the crema was fine-looking (which was of uniform colour compared to the speckles seen in the crema of rested coffee).

hbuchtel wrote:FWIW, in most drum roasters the 'bean temp' thermocouple is positioned fairly high in the drum - with the result that when roasting a very small load the beans will not touch the tc, so the temperature shown is measuring the air temp in the drum rather than the bean temperature.

Regards, Henry

I should have mentioned this. I use a thermocouple in place of the original temperature gauge and make sure there is a sustained contact between the tip of the thermocouple and the mass of the coffee being roasted. Therefore, the temperature measurements I give are bean temperatures (i.e. temperatures of the exterior of the roasting beans).

SUMMARY OF EXPERIMENTS:

(All using the same Mexican bean with the same batch size. All following the same guidelines with good consistency: a 1-minute warm-up, 4-minute drying, fast ramp to first crack -except for the 177C treatment in the case of the final roast, and a final 4-minute fixation of the ultimate roasting temperature, which was originally the main variable)

1. Fast ramp to first crack. 14-to-16 minute total. Reaching up to 210C.
2. Fast ramp to first crack. 14-to-16 minute total. Reaching up to 215C.
3. Fast ramp to first crack. 14-to-16 minute total. Reaching up to 217C.
4. Fast ramp to first crack. 14-to-16 minute total. Reaching up to 220C.
5. 35-minutes treatment at 177C with no airflow and confined roasting environment (funnels closed). 46-minute total. Reaching up to 213C.

SUMMARY OF HOW THEY TASTED LIKE:

1. Offensive acidity, when brewed hot or cold.
2. Offensive acidity, when brewed hot or cold.
3. high/acceptable acidity when brewed cold, high/offensive acidity when brewed hot, with a hint of the burnt-oil taste and smell in the crema.
4. good acidity when brewed cold (possibly with high doses), high/offensive acidity when brewed hot, with apparent burnt-oil taste and smell in the crema.
5. Subtle aftertaste. Very low to no perceivable acidity when brewed hot or cold, with a hint of the burnt-oil smell in the crema (no detectable taste). Note that it doesn't seem that the acidity was balanced by some other component in the taste. It seems as if the acidity has been actually reduced significantly.

MY INTERPRETATION:

It is possible that unlike what we currently think, that the substances responsible of the acrid acidity are more susceptible to breakdown with time rather than with increased temperature (in which the humid roasting environment in a confined drum may or may not play a role). This is demonstrated by the outcome of this series of experiments.

A few points:

Never roast a new bean for espresso, or use it for testing roast profiles, until you have cupped it. The SCAA roasting and cupping protocol is worth knowing even if you don't follow it.

In particular, you need to test coffee for sweetness, ripeness, and a lack of defects. Roast and prepare the coffee as described (215C in about 10 minutes will produce close the specified roast, and a French Press grind at a ratio of 60 grams coffee per liter water steeped 4 minutes will be close to the specified cupping protocol). Let the cup cool for 20 minutes. Now taste it:

• It should taste crisp and clean, neither unpleasantly sour nor bitter. Sweetness should balance the acidity and bitterness. If it doesn't do this, throw the coffee away.
• If the coffee, at this roast, is not sweet enough to drink with fruit or cake; it will not work as espresso, no matter how good the coffee is. There are lots of East African and Central American coffees that taste like great dry wines at this roast. They are wonderful, but moslty hopeless for espresso. Espresso coffees are almost always sweet enough to pair well with fruit or cake at light roasts.
• You should consider getting yourself green coffee that is a know quantity, guaranteed good, and perfect your cupping roast on that. A new crop washed Yrgacheffe, as Peter suggests, is especially good, since it will be grassy if you roast it too fast, a tannic throat closer if you roast it too slow, and a delight if you get it right. Peter's old company, Terroir, sells the same coffees green and roasted. Paradise, PT's and Klatsch do the same. Arranging shipping of the green, then the roasted coffees for comparison, will be expensive, but it's cheaper than flying to Europe or the US and taking a roasting course. I cup an average of 5 to 8 coffees for each one I review on coffeecuppers. Top roasters are even pickier. So you will need to pay attention to your bean sources. Unfortunately, the great majority of coffee is grown and prepped to supply caffeine, not to taste good.

It's likely that the coffee you are working with is bad, or just not right for espresso (it is unusual for a random Mexican coffee to be good, and very unusual for it to be suitable for espresso). In that case, trying to get the roast right is hopeless. All you'll do is become a bean baker (one of those appalling roasters who sucks all the flavor out of every coffee they roast because they do not cup, and learnt to roast for espresso using poor or inappropriate beans)

If the coffee does pass the espresso test, I have a few tentative suggestions that may get the right roast.

• 220C is the absolute minimum for an espresso roast, and 225C is pretty light. Lower than that, the coffee will always taste acidic. The oily liquid you observed does not disqualify the coffee; for espresso roasts you will always burn some surface oils
• There are two sorts of acrid. The effect of chlorogenic acids from a too fast warmup is grassy bitterness at the tip of the tongue and bleach/ammonia aromas. On most drum roasters, this simply does noit happen; the warm up is never too fast. The effect of acridity from an overly dried, too slowly roasteds, or past crop coffee is an acrid, choking effect at the back of the throat. This is often an issue in drum roasters, especialy when a beginner is roasting. If the coffee is good and your upping roast is good, knock off a minute drying and a minute during the first crack and go 5C darker. That may do the trick.

I will do that and report back. However, I would like to discuss more about why would the baking of beans be generally undesirable. If we defined baking coffee as intentionally roasting it in temperatures between 300F and 390F then beyond the development of the nutty/woody flavours and depleting some of the sugars, why would this be considered generally undesirable? The objective of roasting coffee for espresso is to get the best out of the coffee beans (according to this extraction method) and to highlight their origin character rather than highlighting their "coffee" nature. If we agreed on this objective then my question can be translated into: why would baking the beans not serve that goal well, and why would skipping over this temperature range fast and going deep in the roast (beyond 225C) serve it better. I am sorry if I am oversimplifying the matter (turning it into an almost-logical argument) but I would really like to understand. I feel that the Italians, only based on how their brand espresso beans taste like, are accustomed to baking coffee in their roasting heritage, and so I am trying to either find a good reason why this is not a very good idea (in the light of the pre-described objective of roasting) or to start thinking that this might be a cultural variation related to how different nations expect different things from their espresso coffee. I understand that many people may not be very interested in such an argument , but I find myself interested. I already roasted 15 grams of the Mexican coffee I got in 9 minutes (using the modified pop-corn popper) reaching up to 210C, but it has not yet rested.

orwa wrote:However, I would like to discuss more about why would the baking of beans be generally undesirable. If we defined baking coffee as intentionally roasting it in temperatures between 300F and 390F then beyond the development of the nutty/woody flavours and depleting some of the sugars, why would this be considered generally undesirable?

Sigh. Some thoroughly traditional things, like dying in famines, are not worth adopting

The Italian tradition of baking coffee comes from the world wars and depression, when nothing but triage coffee adulterated with grain was available. The best recipes used toasted oats, like the Postum brand. There are lots of people who prefer the taste of Postum to coffee; but my suggestion is that they drink Postum and stop coming up with new ways of destroying perfectly good coffee (toddy brewers, white coffee, double roasting, etc etc)

A US home roasting "tradition" is to come up with ever more appalling roast practices in response to using lousy coffee, never cupped or even brewed, for espresso. This is another tradition worth avoiding.

I presumably "cupped" the thing and my question is now the following: is there such a thing as "ashy bitterness that is caused by the fines suspended in the liquor"? If there weren't such a thing then the liquor I got should have been bitter, otherwise I don't think that the liquor has been either inherently bitter, sour or anything else, i.e., I think that it had a presumably "clean" taste. A brief summary of the situation is that I am not being able to interpret what I have tasted (either positive or negative) due to me lacking any experience in "cupping". Note that I am totally neutral and unbiased to either conclusion. I also tasted the coffee next to pineapples and found the taste acceptable except for the ashy bitterness. I tried both of my Zassenhaus Turkish grinder and the other hand grinder for the cupping and noticed that the ashy bitterness may be resulting from the fines. I have another hand grinder that doesn't produce any fines but the problem with it is that the grind is very coarse (maximum particle diameter around 5mm, average around 1.5mm, very coarse), which I have not used. Using this grinder I am usually able to produce a liquor that is light in colour (tea-like) with a clean taste, but I did not use it this time because I depleted all of the 15 grams I roasted using the other two grinders (using 8 grams for 245 ml of water at a time). I am sorry if I am providing an excessive amount of detail but obviously it's because I have no experience and happens to be in a position where I need to carry on a test that I don't know how to conduct.

I am a little embarrassed to add that I went through another horrible roast in which I stayed at 180C for 10 minutes before ramping up to 200C and staying there for some time, then ramping up to 205C and ending the roast. I would like to confirm that the beans don't pop in such circumstances and that the acrid, ammonia-like acidity gets removed completely with no choking aftertaste in this case (this roast was 26 minutes in total). Note that I used a fan speed of "2" for the length of the ten minutes I spent at 180C. The interesting observation at this time was that the droplets of condensed roasting vapour had an intense, ammonia-like acidic smell that matches very well the defect that I have been trying to eliminate in the taste (same smell I used to experience upon opening the door of the oven when I was roasting using ovens). I think that this means that the substances responsible of the acrid acidity have been dissolved and carried away by the confined, moist roasting vapours. Of course, I do not want to be a lousy roaster and be proud of it, but I cannot resist proposing the following theory: Could it be that the chlorogenic acids (melting point: 206C-210C, some are soluble in hot water) are getting hydrolysed due to the circulating, moist roasting vapours resulting in quinic acid (melting point: 166C-168C, water soluble) which is then being dissolved and carried by the moist vapours -thus getting removed from the beans? (quote: "Quinic acid is also implicated in the perceived acidity of coffee", says Wikipedia). Now assuming this fairy tale was correct, then an extended drying phase at 338F (or maybe less) with a moist roasting environment may do the trick. In either case, I did not succeed in removing the acidity in temperatures below 300F and so I would like to humbly state that I don't think that the removal of the acrid acidity is correlated with raising the temperature beyond 390F or prolonged drying below 300F (not having these as direct cause). My speculations of the underlying transformations are probably incorrect, but this must not be confused with the fact that I am having great success eliminating the acrid acidity using some baking-based methods.

another_jim wrote:A US home roasting "tradition" is to come up with ever more appalling roast practices in response to using lousy coffee, never cupped or even brewed, for espresso. This is another tradition worth avoiding.

Not anymore! It seems as if it were a Saudi-Arabian tradition as well .