Roaster Carbon Calculations

The good people at Fresh Cup used the U.S. EPA Carbon Calculator to compare the Roastaire Carbon Footprint with that of a gas roaster.   

A 100 lbs.  of roasted coffee = 1 car off the road for 16 days  

This is how our roasting method impacts the environment. The energy ratio is  2 light bulbs versus the drum roasters 48 light bulbs.  Gas is a cheaper form of energy therefore in dollar terms the approximate heating cost of a gas fired roaster with afterburner is 16¢ per pound vs. the 2.5¢ for the recirculating Roastaire.


Evidently the Roastaire is way more environmentally friendly and cheaper to operate.  


The 100 lbs. of roasted beans represents about 3 hours of roasting, depending on the degree of roast.  Think of the savings to the environment and to the owner.  


It's time for a cup of freshly roasted coffee and a read about selling carbon credits.

High Pressure & High Temperature Industrial Blower

The suggested applications required either high temperature or high pressure but not both.  Googling the terms "high pressure" "high temperature" Blower brings up every type of air mover imaginable.  The designations are quite "loosey goosey" and often stretched so that it will accommodate the particular product being offered for sale.


I expected that this blower rated at 250°C would be at the bottom end of high temperature blowers but no - some units were given the same designation yet could only operate at temperatures that were 100°C lower.  


Some units had operational ceilings that were twice as high as what this one was tested at but their "high pressure" turned out to be .3 psi or 2,070 pascals which implies that it turns relatively slowly.  Low speeds are attainable with off the shelf bearings.  Therefore, it is not a niche that is of interest.


The version pictured is currently on the test bench where it is subjected to high temperature moist air.  Previous tests of off the shelf blowers demonstrated bearing corrosion in less than 100 hours.  It is possible that had it been a continuous test the bearings would have survived longer but running tests that lasted a few hours compromised the bearings too soon.


We are currently using the blower to fluidize and roast beans (coffee and others).  The pressure output of over 1 psi ( 6,894 pascals ) at 250°C  could certainly fluidize denser materials at a lesser depth.  At these temperatures the blower could be the heart of a monstrous pop corn pumper.  With continual introduction of kernels the output will compete with Vesuvius.  Such a machine would have to be brought to corn country Taber for testing.  


A recycled hot air requirement is fundamental to this niche, otherwise it is more efficient to heat the air after the blower i.e. an air knife.  Now, if a high temperature air knife was in a closed system nearly every blower in the marketplace would be inappropriate.


Hot air accelerated drying in an industrial setting would require a moisture extraction process but if it is a recirculated hot air application this is a custom application.  


Have a freshly roasted coffee and think of another application for the unit.

Packaging - Optimism

Packaging attempts to circumvent or overcome the stalling of coffee.   It does not keep old coffee fresh though it is claimed that it slows down the staling for an unbelievably long time.  Most of the advantages are perceived by the consumer based on sizeable advertising programs.  Though it appears that a valve, at least under ideal conditions, lets little air into the bag.  Well, less than the bag would have had when it was sealed.  Vacuum sealing reduces the air and moisture in the bags but that requires more equipment and time.  The valve does let out the CO2 but it also lets the aroma escape.  The vented bag will have a lower internal pressure, than say a metal container.  The lower pressure exacerbates the loss of volatile compounds which are the reason for that olfactory experience.  To circumvent that loss some companies replace the vent by Oxygen and/or CO2 scavengers.

"Espresso Coffee" by Illy & Viani states that the spoilage rate increases by 7 fold with every 10°C increase in temperature.  Unfortunately there is no mention if that calculation starts at absolute zero. It is an unmeasured and uncontrolled variable that very much affects the coffee experience.

A lot of money was invested into the marketing of various types of packages because the business model of central roasters depends on convincing customers that coffee that is more than a year old still has the freshness of yesterday's roast.

I view the valve as a packaging solution which does not contribute much to maintaining the roasted bean's fresh taste.  My only acceptable solution is to buy the freshest coffee from a local roaster.  An exception, in Canada, is Freshcup.ca which ships, via expedited post, the day the coffee is roasted.  On several occasions I have sent some much appreciated coffee gifts.  It could be perceived that I am biased because they use our roaster though I maintain that the long relationship has allowed me to observe closely the organization and witness their commitment to delivering the freshest great tasting organic coffee to their customers.

Do Coffee Bags "Lock in the Flavour" ?

The test will be posted in a few phases, perhaps more if there are leakage problems around the valve, such as the testing apparatus, results, and implications of the findings.

To the left is the inside part of a Check Valve that is incorporated on many coffee bags.  It permits the coffee roaster to bag the coffee very soon after roasting.

For those who may not be aware, freshly roasted coffee releases CO2 (Carbon Dioxide) in the days that follow the roasting session.  The pressure is sufficient to burst bags.  Initially the coffee was packaged in various media such as paper and consequently not hermetically sealed.  Some roasters "aged" the coffee and packaged it several days later when the CO2 had been dissipated.  The Check Valve is a more recent development which allows the CO2 to escape without splitting the bag.  There could be an advantage to this method if the valve is placed such that when the filled bag is stored the valve is the highest point of the bag.  CO2 is heavier than air therefore it will gravitate to the bottom of the bag forcing out the lighter air first.  Technically it is possible that all the oxygen could be forced out in this way.

The purpose of this test is to verify the premise that the Check Valves are more important to the marketing campaigns than to preserve coffee or "locking in the flavour".  Does a valve costing about a penny do the work of precision devices?  If the bag is not hermetically sealed the constantly changing atmospheric pressure will make the bag "breathe" which will introduce oxygen to the contents. 

The apparatus is quite simple and will involve measuring a Control to be certain that the test equipment is leak proof.  The upper left barbed fitting will be connected to a vacuum pump then the valve will be closed.  The Needle Valve is rated at 6,000 psi therefore it should not be harmed by this test.  The vacuum will be measured by water movement in a U tube.  The picture shows two devices that can be sealed to the bag.  The preferred socket is the one to the right which is machined with steps that will fit just over the valve so that it is not distorted or twisted.  This is better than in reality where the valve is pushed by the beans.  Several different sealing materials may be required before a good seal is established between the socket and the plastic check valve.

Plotting the height of the water column should be a good indicator of the leakage rate, if present.

Marketing departments are notorious for making unsubstantiated claims.  Rather than admit error the trend is to spend more money to embellish their fabrication.  Let's check the foundation to the claims.

Freshly roasted coffee does its own marketing.

                                           -------------------------------------------------

The first phase is Testing the bag's Venting Valve in Ideal Conditions.  

The venting valve was cut from a new bag (unfortunately that is a sacrificial test) but a lots of material was left on either side of the valve.  The valve was then mounted to the socket and sealed with a thin layer of silicone adhesive on the periphery.  The adhesive cured overnight. 

A slight vacuum ( 33.5" H2O or 851 mm of H2O) was drawn against the valve.  That is P1-P2 = 67" H2O (1.702 m) in the U tube manometer.

After an hour the water column was 1" (25.4 mm) lower which represents 1.81 cc of water.

After an 2:45 hours the water column was 1.5" (38 mm) lower which represents .165 in3  (2.7 cc) of water.

After an 6:00 hours the water column was 3" (76.2 mm) lower which represents .33 in3  (5.43 cc) of water.

After an 47:00 hours the water column was 9.25" (235 mm) lower which represents 1.022 in3  (16.74 cc) of water.

After an 70:00 hours the water column was 9.88" (251 mm) lower which represents 1.091 in3  (17.89 cc) of water.

Granted the Control Run has not been done.  Under ideal conditions it is little leakage but then it is over a short period.  The pressure, however, is considerably higher than the barometric fluctuations.  So far it can be established that it is not a hermetic seal.  To reflect the packaging role the pressure may have to be reduced, the time period increased, and the valve will have to be pushed against beans rather than held flat in a socket.

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More on a newer blogs Vented Bags Revisited  and Packaging - Optimism

High Temperature Industrial Blower

"Delivering the air with sufficient pressure at 240°C is a challenge that will be addressed in a later post.  Sufficient to say that no off the shelf hot air blowers were found, resulting in another product development." from the earlier post Heating Coffee Beans to Roasting Temperature.


Note:  A fan generally turns slower than a blower and therefore cannot reach the same pressure differential (inlet / outlet).  Fluidizing a batch of coffee requires more pressure than a fan delivers.


The easy, but wasteful, way to circulate hot air is to heat it after it passes through the blower.  This means that all the air has to be heated from ambient temperature to final temperature before it is vented while, if the air is recirculated, only the lost heat needs to be replaced.  The higher the temperature the more efficient the recirculation process becomes.  The advantage is not a few percentage points but rather tens of percentage points.


Our prime interest is roasting coffee which becomes much more efficient when the heated air is recirculated.  No off the shelf unit could be purchased.  Initially we tried then modified an existing name brand blower.  The MTBF (mean time before failures) improved from the initial few hours to over 1,500 hours but the maintenance and problems required a new solution.  The concept was simple but mastering the quirks was not always a linear process.


The designed temperature ceiling for the current model is 300°C but it has only been operated up to 270°C.  Since we did not find this to be an optimum roasting temperature the importance of establishing a higher operating threshold lost its urgency.  There is reason to believe that the upper temperature limit can be raised significantly.


Apart from surviving the high temperature the priority is to develop sufficient pressure to create a fluidized bed so that the coffee beans are evenly heated and continually mixed.  The pressure, while roasting, is just under 1 psi (approximately 6 kPa).  This is the flowing pressure not dead head pressure.  


The current blower configuration is driven by a 3 Hp electrical motor connected to a three phase contactor based motor controller.  The Belt Guard Cover was removed for the photo.


Have a freshly roasted coffee and think of another application for the unit.

Heating Coffee Beans to Roasting Temperature

In cooking the heating process is usually prescribed by the recipe.  Yet, there are reasons why certain chemical reactions are promoted by heating method and temperature.  Common sense tells us that a Blow Torch is not a good heat source for warming the body.  The high temperature differential means that the outside layer will burn before the inside is warm.  Perhaps the Blow Torch salesman would suggest that the body whirl like a Dervish near the flame to distribute the heat.


In "Espresso Coffee" R. Eggers writes the typical gas temperature of a drum roaster is 400° - 550°C.  The high temperature cooking analogy for beans hit by the super hot air is frying eggs while using the stoves highest heat setting.   To this end the Roastaire uses a fluidized bed in which 240°C (adjustable as required) air is pushed through the beans.  This significantly increases the heat transferred to the entire batch of beans.  The beans have a limited ability to absorb the heat therefore the temperature gradient is more uniform throughout the batch with the forced air stream.  The added benefit is that the air flow continually churns the beans and carries away the chaff.


Considerable research has been done to understand the dynamic and continually evolving variables in the coffee roasting process.  In the design phase, of the Roaster, the limitations of the bean and the requirements to start the chemical reaction, referred to as roasting, determine the roasting precepts.  We do not believe in using extreme 400°C plus air  temperature that mostly moves around the batch of beans.  The beans will burn on the outside before it is hot inside.  Agreed the beans are in motion and only subjected to intermittent burning temperatures.  The average may be arithmetically acceptable but then so is keeping half your body in ice while the other half is in boiling water.  Perhaps some manufacturers slavishly follow this century old trend because it is easy and obvious.   


The starting point of the exothermic reaction ( above 180°C according to R.Eggers and at 200°C according to Clarke & Macrae).  We commonly use an air temperature of 240°C delivered under pressure so that the air is forced through the batch without initially losing more than a few tens of degrees.  The heat transfer to the beans, is slightly higher at the beginning of the roast when the beans are denser and able to transmit more heat internally.  Initially the heat absorbed serves to evaporate the moisture which determines the heat slope (how quickly the beans increase in temperature).  The decrease in bean density reduces the heat absorption by the beans hence the air temperature is rather uniform for the first and last layers.  Actually when the exothermic reaction begins the heat generated in the first layers raises the temperature of the beans that are down stream.   Delivering the air with sufficient pressure at 240°C is a challenge that will be addressed in a later post.  Sufficient to say that no off the shelf hot air blowers were found, resulting in another product development.


The Blower's pressurized air heats the beans and mixes them with a "bubble action" which helps reduce the contact of beans and the hot metal sides of the Roasting Chamber.  Some home roasters tout the advantage of their fountain mixing of the beans which is not optimal for roasting.  A fountain is created when the air flow is concentrated in one area which means that the air is not flowing through the rest of the beans i.e. not heating them evenly.


Time for a freshly roasted coffee.  Agree?