Ask the Alchemist #186


Today is a bit of a departure from my classic Ask the Alchemist.  I am sharing a conversation I had with a customer over some time.  This is the kind of thing I do every day and what inspired the Ask the Alchemist series in the first place nearly 4 years ago.  I thought about cleaning it up but found the back and forth nature of the conversation very appealing.

Level: Alchemist

Reading time: 15 min

Hi Alchemist,
 Thanks for replying to our request for help with roasting conditions for our new roaster.
As mentioned in message, my son and I have been making chocolate for the past 2 years on our family cocoa estate in Gran Couva Trinidad. We are self taught chocolatier and spent much time on your website which was very informative.
We started with Cocoatown junior roasters which we set thetemperature of about 350 F, we roast our Trinitario beans in that roaster for 20 mins then half open the cover and roast for a further 15 minutes. We think that was a fairly heavy roast and may have driven off some of the finer flavors.
We recently bought a Cocoatown commercial roaster with temperature control and are seeking some guidance as to how to determine the best roasting conditions. Any advice you can provide would be greatly appreciated.
As a starting point we are using a roasting profile of 20 minutes at 300 F , then 20 mins at 150 F and 10 mins at 120 F. The beans are roasted right through with the outside being a light darker than the inside. We have a dial thermometer fitted through the drum which measures the inside temperature which shows a max temp of about 150 F and then falls off to about 120 F at the end based of the roasting conditions mentioned above.

 A quick question before I delve in.  Are you saying the beans are 150F at the end?

 Also would you tell me what the power ratings on both the Junior and commercial roaster are, along with how much you are roasting with each?

 The power on the junior roaster is 1250 watts and the big one is 2700 watts.

We inserted a dial thermometer through the holes in the roasting drum so it's stem goes almost to the center of the drum but the dial face with the readings are on the outside of the drum. This reading goes but the 150 F max when the beans are added, even with the roaster temperature setting at 300 F, it stays around 150F right up until we lower the temperature setting to 120 F for the last 10 mins, during which it will gradually drift down to 120F by the end of the roast.

We preheat the empty roaster at 300 F for 15 mins before adding the beans.

We roast 6 lbs of beans in the junior and 20 lbs in the bigger one.

Is the thermometer in the bean mass?  Or is it in open air?

I'll delve way in after knowing what that temperature refers to, but those roasters sound WAY under powered.  I do 6 lbs in a 2000 watt roaster and prefer roasting 5 lbs.

The end of the thermometer is in the bean mass, the beans tumble all around the tip of the thermometer.

I'm kind of fearful I am not going to be of much help here.  This is what I'm hearing:

 "We recently bought a Cocoatown commercial roaster with temperature control and are seeking some guidance as to how to determine the best roasting conditions. Any advice you can provide would be greatly appreciated.

As a starting point we are using a roasting profile of 20 minutes at 300 F , then 20 mins at 150 F and 10 mins at 120 F."

That is a 50 minute profile.  Which although i guess some people do that, that seems like a terribly terribly long roast, one that is going to leave the chocolate pretty flat in flavor.  But on the other hand you mention you never see the beans get above 150 F. That is so low as to not be roasted.  You are kind of doing a low bake on the beans.

So, let's do a little back and forth here.  Why are you dropping the temperature first to 150 F and then to 120 F?  If you had said 250 F and 220 F I might have said, ok, that is a bit light, but if you like it fine.  But under 200?  I can hardly give advice there.  Those sound nearly raw yet baked.  Dehydrated almost.

Personally I would want to see the roaster roasting about 10-15 lbs of beans, with the temperature up at 350 F initially, and the chamber never dropping below 250 F, stopping the roast when the beans are roughly 240-250 F hopefully in a time of about 30-40 minutes (really 20 minutes but that roaster isn't capable).  I will help however I can but I'm not sure this roaster has 'best roasting conditions'.

 I understand what you are saying about the wattage of the roasters, we did not consider that when doing our selection. The commercial roaster can be set higher, dial shows up to 550 F.
When we used to use the junior roaster with fixed setting at 350F for 35 mins it used to burn the outside of the beans. Turning some of them very dark and giving the nibs a bitter burnt taste. We then started half opening the lid after 20 mins to extend the roast so the inside of the bean would cook but not burn the outside.
So when we got the commercial roaster with the variable temperature we thought let's start lower 300F instead of 350F in junior, and then drop the temperature to mirror what we achieved by opening the lid of the junior. We never used to measure the temperature inside the drum of the junior.
We know very little about roasting conditions and so perhaps we should forget what we did in the past and ask the question---- if you were to roast some Trinitario beans what conditions would you recommend and let's see if we can achieve that. As you suggest we can do smaller amounts to get the wattage per lb higher. Now that we can measure the temperature inside the drum, that's the bean temperature I guess, let’s base our conditions on that.
In the mean time we will try roasting 10-15 lbs of bean at a setting of 350F and doing it until the beans temperature reaches 250F.

As a comparison, having not looked at the wattage or power but only the dial, it is like buying a car because the speedometer goes to 120 mph and then being surprised it won't go that fast only to find out it is a 50 hp motor, not a 300 hp motor.  Once you know that it is no surprise it won't go fast.

The darkening of the beans is curious.  Is the drum turning slowly?  Under 10 rpm?

We did the test roast that you suggested and the results were very close to what you predicted.

Warmed roaster to 350, added 10 lbs mixed medium to small beans as we just checking heat capacity of roaster. Set roaster at 350 F, after 10 mins bean temp reached 175F , increased temp setting to 450F after another 10 mins bean temperature reached 215. Increased setting to 550 which is max for roaster and after another 10 mins temp reach 250 stopped roast, total roast temp was 30 mins.

We were surprised that considering the smallish size of the beans they were not more burnt, some were differently dark brown/black on the outside.  There was also a strong 'brownie' smell.

These conditions might be ok for our normally larger beans.

That sounds right!  Except the burnt part.  But I'll simplify something for you. Those in theory ramps you did (with the exception of the first one) effectively did nothing at all.  They are ONLY thermostat set points.  Look at how the roaster sees it.

  • 350 F - Is the roaster at 350?  Yes, turn off.  No, keep heating.
  • 10 minutes - Is the roaster/beans at 350?  No, they are at 175 - keep heating.
  • 10 minutes - Is the roaster/beans at 450? No, they are at 215 - keep heating
  • 10 minutes - is the roaster/beans at 550?  No, they are at 250 - keep heating.

In other words, since you never hit 350, ever, you could have left the thermostat there and it would have kept heating the whole time and the roast would have been 100% identical.

Back to the car anology.  It's like putting it on cruise control for 100 mph.  If you can't get over 50 mph no matter what, the car does not care if the cruise control is at 55 mph or 200 mph.  It's going to give it full gas the whole time.

See what I mean?

I am really dismayed to hear how under powered and how much misinformation cocoatown has put out about their roasters.  It feels like false advertising.  20 lb roaster? No.  Temperature profile control?  No!  And you probably going to constantly struggle with tipped beans (meaning uneven roast) since it rotates so slowly.

That all said, I'm glad you roasted well.  10 lbs sounds like a good load.  Please let me know how the chocolate they make tastes.

Thank you for helping us understand these roasters a bit better, I am sorry we didn't chat before we purchased the one we did, it clearly has its shortcomings.
In conclusion, are you saying that the way to roast Trinitario beans is to use a high setting on the roaster and bring the bean temperature up to 250 F, in 20 mins if possible or 30-40 mins if that's the best the roaster can do, then cool the beans down and that's it?
I thought that a roasting profile which starts high for a while then drops down, roasted the beans right through without loosing the flavor notes.
Also we got a strong 'brownie' smell at the end of the roast. We thought that was bad as it shows we were running off bean flavors.

Taking this a bit backwards, I thought you were referring to my site when you noted brownie smell.  That is a good thing.  It is my hallmark of a proper roast.  THE hallmark of most good roasts.  Never, ever a bad thing.  It means you have actually developed the chocolate flavor and now some is vaporizing and you can smell it.  It isn't like it existed previously and you are driving it off.  Gases (what you smell) by definition are very diffuse.  Most aromas you smell are only at 1 part per billion in the air.  At least in many cases.  Meaning, sure, you smell something, but there is a billion times that left in the bean.

Think of roasting a chicken or anything else. It smells wonderful.  And you never think you are driving off the flavor when you smell it do you?  No, you think, "ah, that's starting to smell done!".  Sure, you can drive flavors off if you over roast, but you have to actually over roast.  That would be a bean temperature well over 300 F for most beans.

Overall you have the roasting correct.  And it isn't just for Trinatario.  It is for any beans.  Only the final temperature changes a little.  245 F for some Criollo, 265 for some Forastero.

Here is the thing with roasting hot and cooling down.  That only applies if the roaster is capable of roasting what you put in it.

Car analogy again.  You need to get to 60 mph.  On a hill.  And stop just after you reach the top.  You have two cars.  A high powered Mustang and a low powered Pinto.  If you floor the Mustang, you are fine heading up the hill.  But you have to let off the gas or you will over shoot the hill top and run out of control.  The Pinto though can barely make it up the hill.  You have no choice but to give it all it can the whole time.  And it will probably take you longer to get there.  And because you are going so slow, you can still easily stop.

This is why you can only roast a couple pounds of beans in a standard home oven.  Although it can get to 550 F over time, it can't do it fast.  The heat input is too slow. The power is too low.  So you have to only put a a few beans in so you minimally affect the temperature in the oven.

Finally, you have to think of power not temperature.  They are two completely different things. 

Say you have a 5 gallon water bucket with a 1/4" hole in it.  Temperature is a measure of how full the bucket is.  Power is a measure of how fast you are filling the bucket.  Your roaster is filling the bucket with a little 1/2" hose.  No matter how open the valve is, it can only fill so fast.  And a lot of the water is going to drain out (heat loss and bean load) and it's almost impossible to fill the bucket to over flowing in the time needed for a good roast.  A good roaster that is loaded properly has a 2" hose filling it and can overflow the bucket quickly. So you have the water valve fully open for part of the roast (mixed analogy there), then start to close the valve to keep it in control, slowly and steadily filling the bucket.

How's that?  Am I repeating myself too much? My intent is to get you a mental image so you have a feel for what is happening.

Have you watched my three roasting videos?  Kind of long, but it they go over oven, Behmor and drum roasting.

http://chocolatealchemy.com/how-to-make-chocolate-the-complete-text-guide#cocoa-bean-roasting

If you can follow the maths I go over them in detail here.

http://chocolatealchemy.com/blog/2016/09/22/ask-the-alchemist-177

 

 

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