Question and Challenge What you Read

Company Blogs which very often are prone to being commercials should not be taken at face value or believed without reflection and sometimes, some research.  

One blogger (Blogger B) submitted a comment to a competitor " I read with interest your article entitled “Roasting with Hot Air: Benefits of Air Roasters” in your company’s newsletter."  He then proceeds to authoritatively expound on his own lack of knowledge in the roasting process.  The complication here is that the article, by Blogger A, he refers to has some rather glaring falsehoods i.e. "During the roasting process, the green coffee beans go through two major “pops” or “cracks” The first occurs when the internal temperature of the bean reaches approximately 356 degrees fahrenheit.".  The problem here is that no matter how long you boil water the temperature remains no higher than 212°F or 100°C.  The evaporative process greatly slows the bean from continually increasing in temperature until virtually all the moisture is evaporated.

It appears that Blogger B then proceeds to confuse degrees Fahrenheit with degrees Centigrade.  Blogger A writes "This hot air reaches temperatures of between 450 and 485 degrees fahrenheit" (232°C to 251°C) which is slightly above the 195°C to 205°C where the beans undergo an exothermic reaction.  A much lower temperature would essentially bake the beans.  Despite Blogger B's assertion that the air roaster is way too hot it is 100°C to 200°C less hot than a typical gas fired drum roaster.  It is true that the air roaster has a faster roast cycle but 4 minutes is absurd while 11 minutes is quite normal because the heat is quite evenly applied to all sides of the bean as they are churned in the fluidized bead.  Drum roasters only have fans which are incapable of pushing the air through the batch of beans therefore they only heat the top layer, the beans touching the drum, and beans that are falling off the rotating blades.  Blogger B's comments "Regardless of how heat is applied to the outside of the beans, heat reaches the insides of the beans by conduction. And, when it comes to heat conduction, coffee beans are not very good at it. Therefore the development of the insides of the beans always trails the development of the outsides of the beans."  Ironically he is presenting a case that favours the lower temperature of the air roaster (for the same reason you do not fry eggs on high settings).  This, however, is not true for the entire roasting session.  The heat moves inwards in the endothermic phase until the bean enters the exothermic phase.  

Think of lighting a damp piece of paper.  There is a reason why you can boil water, on a flame, inside a paper bag.  It is because the water seeping through the material prevents the paper from reaching its combustion point.  However remove that water, the paper will dry, and will then burst into flames.

Blogger B apparently does not realize that a full roast includes the exothermic phase where the heat is generated inside the bean.  See sectioned bean photo.  At this point the roasting process has to be monitored closely to "kill the roast" at the right time.  We prefer to cool within the Roasting Chamber because it is quicker and easily repeatable.  At this stage the transformation is very rapid therefore it is challenging to guess "the kill point" half a minute to a minute in advance because it takes that long to dump the beans never mind cool them.

Blogger B also comments on the single pass air roaster even though his system not only is a single pass air supply but it is roasting with the exhaust of the flame.  Imagine cooking supper with the car exhaust (maybe a propane powered vehicle is slightly more appropriate", it will certainly contribute all kinds of flavour.  Recirculating hot air cannot be done with a gas fired roaster because it starves the flame.  We do it in an electric roaster but it took five years to develop a blower that would survive the temperature.   Re-circulation improves the efficiency and makes it possible to significantly cut emissions.  

A gas fired Afterburner burns on average 3 times more gas than the roaster.  It decreases the visible smoke but really loads the exhaust with volatile organic compounds known as pollution.