Transition from vegetal flavor during first crack - Page 3

[GDM528]

From a non-exhaustive review of literature, the mystery compound may be hexanal. See this article, https://doi.org/10.1016/j.foodchem.2016.04.124.

One method to investigate further would be to buy a standard and spike a small amount at different concentrations into a sample without this defect (test samples), and compare to the same sample without a spike (negative control) and to a sample with known defect (positive control). https://www.sigmaaldrich.com/US/en/product/sial/18109

The boiling point for hexanal is 130C. Won't most of it be gone by the time it reaches first crack, or be released immediately upon first crack?

[drgary (original poster)]

I would think it's still trapped within the cellular matrix and not even fully released during first crack. You would need to reach a temperature where it breaks down throughout cell tissue.

[Marcelnl]

That is also my expectation, interesting experiment ! Wish I had access to a full blown lab, could go crazy on coffee!

[Almico]

I wouldn't mind having a gas chromatography mass spectrometer in my roaster. I wonder if any of the huge roasting companies do. It wouldn't need to analyze a broad spectrum of compounds in the exhaust gases, just the few that we really care about.

Short of that, we are left with rudimentary temperature probes, trial and error and what works and what doesn't.

I was always intrigued by the Nordic approach to roasting and how they manage to roast coffee so light and yet still avoid underdeveloped flavors. In lighter coffees the spread between roast color inside and outside is much greater than with darker roasts. These off-putting chemicals that we desperately need to manage are likely eliminated from the outside first to the inside last. If a roast is dropped before the inner part of the seed has reached the necessary temperature, then the result will be unpleasant. Remember, we only measure the outside bean temperature, and barely that.

In a presentation at Brooklyn Coffee Roasters a few years back, Rob Hoos mentioned a theory that the time that it takes pressure to build up in the coffee seed can have a significant effect on the speed of heat transfer from the outer to inner. Like a pressure cooker, the faster that pressure builds before it has a chance to be released, the greater the transfer of heat progresses through the seed.

I experimented with this a couple of years ago and by hitting DE in 4 minutes or less in high density beans I was able to drop coffee around 10*F above FC in around a minute. The coffee was so light that it jammed my Monolith conical burrs, not an easy feat, yet there were no signs of vegetal or underdeveloped flavor notes. The coffee was very acidic and lacked the body I prize, but very drinkable. Just don't try and put milk in it.

I did this with a variety of coffee varieties and origins and got similar results.

What I lost was the variation in flavors present when coffee is roasted a bit more. It seems the darker and darker you roast coffee, the more generic it tastes from a roasty standpoint, and the lighter and lighter you roast coffee the more generic it gets in the "lemon juice" realm.

So after achieving my goal of being able to roast much lighter than I liked without the unpleasantness, I've swung the pendulum back in the other direction a bit and seek the subtle complexities available when roasting a bit more than the lightest extremes.

[Milligan]

Heating the bean thoroughly and evenly is a line we tread on the light roast side. I was wondering a few days ago if anyone has tried cutting/sectioning raw whole beans into smaller pieces and then roasting those. I'm not sure what appliance would be used to get a uniform sizing. You'd likely get a faster and more even roast due to the larger surface area. FC may sound completely different or not exist at all. Perhaps it would more quickly develop an even roast at a lower temperature to eliminate the vegetal qualities. An interesting experiment of particle uniformity could be achieved.

[Almico]

I don't think evenness from inside to outside is the goal. I think the variation adds complexity. But the inside needs to "finish".

[Trjelenc]

Heating the bean thoroughly and evenly is a line we tread on the light roast side. I was wondering a few days ago if anyone has tried cutting/sectioning raw whole beans into smaller pieces and then roasting those. I'm not sure what appliance would be used to get a uniform sizing. You'd likely get a faster and more even roast due to the larger surface area. FC may sound completely different or not exist at all. Perhaps it would more quickly develop an even roast at a lower temperature to eliminate the vegetal qualities. An interesting experiment of particle uniformity could be achieved.

Don't forget that coffee bean is not like a cut of meat, in which the cross section is uniform in its matter. The bean interior will have higher concentration of "reactive matter", so I'd imagine you'd find easier scorching (or just darkening) on the sides of the particles that were the bean interior. Almost like preblending washed and natural and expecting a uniform color

[Marcelnl]

I wouldn't mind having a gas chromatography mass spectrometer in my roaster. I wonder if any of the huge roasting companies do. It wouldn't need to analyze a broad spectrum of compounds in the exhaust gases, just the few that we really care about.

Short of that, we are left with rudimentary temperature probes, trial and error and what works and what doesn't.

I was always intrigued by the Nordic approach to roasting and how they manage to roast coffee so light and yet still avoid underdeveloped flavors. In lighter coffees the spread between roast color inside and outside is much greater than with darker roasts. These off-putting chemicals that we desperately need to manage are likely eliminated from the outside first to the inside last. If a roast is dropped before the inner part of the seed has reached the necessary temperature, then the result will be unpleasant. Remember, we only measure the outside bean temperature, and barely that.

In a presentation at Brooklyn Coffee Roasters a few years back, Rob Hoos mentioned a theory that the time that it takes pressure to build up in the coffee seed can have a significant effect on the speed of heat transfer from the outer to inner. Like a pressure cooker, the faster that pressure builds before it has a chance to be released, the greater the transfer of heat progresses through the seed.

I experimented with this a couple of years ago and by hitting DE in 4 minutes or less in high density beans I was able to drop coffee around 10*F above FC in around a minute. The coffee was so light that it jammed my Monolith conical burrs, not an easy feat, yet there were no signs of vegetal or underdeveloped flavor notes. The coffee was very acidic and lacked the body I prize, but very drinkable. Just don't try and put milk in it.

I did this with a variety of coffee varieties and origins and got similar results.

What I lost was the variation in flavors present when coffee is roasted a bit more. It seems the darker and darker you roast coffee, the more generic it tastes from a roasty standpoint, and the lighter and lighter you roast coffee the more generic it gets in the "lemon juice" realm.

So after achieving my goal of being able to roast much lighter than I liked without the unpleasantness, I've swung the pendulum back in the other direction a bit and seek the subtle complexities available when roasting a bit more than the lightest extremes.

I struggle understanding why the speed of pressure build up would impact the speed of heat transfer, I'm inclined to think that the time taken to reach a certain pressure has less effect than the pressure itself being driving force for heat to be conducted by whatever means unless there is still a lot of water contained within the bean (as a result of fast pressurization)

[DeuxInfuso]

Allow me kind sirs to humbly suggest a mechanism: coefficient of thermal conductivity is proportional to density, all else being equal (in an unroasted/semiroasted coffee bean), and water vapor/steam density is likely the major thermal transfer agent. Fast thermal ramp may more effectively drive a hot wave of steam inward, relative to a slow thermal ramp, due to steam loss/dessication/steam off-gassing outward (time & entropy never sleeps) causing loss of thermal wave momentum (steam density/energy) if thermal ramp is slow.

So ponders a twirly pop popcorn roaster with 300 kg experience in 7 years of weekly manual roasting practice.

-Deuxinfuso

[Marcelnl]

sounds plausible, as pressure buildup might form a kindof wave front allowing the energy/heat to transfer faster when pressure buildup is faster, I did not factor in/think about how the pressure behaviour of the inside of a bean would look like...