A primer for heatgun/dogbowl coffee roasting

by Michael Lloyd

The earliest mentions of using a heatgun and a roasting vessel to roast coffee go back to the early 1990’s on the Net and in the alt.coffee Usenet newsgroup.   Attaching a roasting chamber filled with coffee beans to a heatgun muzzle goes back even further.  This technique, developed by Michael Sivetz to roast coffee samples, uses the Wagner HT 775/Milwaukee 750 heatgun still available today.  

Since the last quarter of 2003, this older method has become more popular.  Why the sudden upsurge in interest over the heatgun?  Theories abound, but one possible reason is a backlash against expensive and unreliable roasting appliances that often do not work well out of the box and can require juryrigging or additional equipment to obtain good results.  By contrast, the heatgun method has low entry costs and the equipment is simple and robust, producing a significant throughput of a quality roast.  It combines elements of both an air fluid-bed and conduction roast.  Roast times can be controlled to produce a quicker, brighter roast or a slower, fuller roast.  Thus one simple and inexpensive equipment setup can replicate either an air roast or drum roast.  This method is probably the cheapest means of producing significant batch sizes at nominal costs.  The closest competitors are the HotTop at $ 600 and roasting nine ounces, the AlpenRost at $ 280 and roasting eight ounces and BBQ grill roasting drums at $ 125-210 and capable of roasting up to four pounds on your existing gas BBQ grill.  

Through the efforts of an intrepid group of experimenters at Coffeegeek.com, to include Martin Lipton, Jim Liedeka and Michael Lloyd as the early adopters, the heatgun method has recently undergone a great deal of refinement and some recommendations are presented here on equipment and technique.  Michael Lloyd is the originator and author of this primer and any mistakes are entirely his.  The intent of this primer is to allow someone with basic roasting experience to use the equipment and techniques described here to get a good roast from the very first. 

As with all methods of coffee roasting, the heatgun method involves high temperatures and care should be taken to avoid personal injury and property damage.

Here are some pros, cons and basic equipment of heatgun/dogbowl roasting to think about:   

Basic equipment needed:

• Heatgun

• Roasting vessel

• Stirring utensil

• Metal colander or other cooling method

Pros:          

• Entry costs are low

• Excellent control over roast

• Capable of large batch sizes (5 to 16 oz.)

• Necessary equipment is simple and robust

• Easy to monitor the roast

• Able to immediately halt roast at any point

• Can roast 2-3 lbs. per hour

• Even roasting

• Quality of results dependent on operator technique

• Rapid learning curve

• Allows user to determine a range of fluid bed to drum roasting conditions and results by varying airflow and length of roast

• Easy to roast small amounts for blending
  

Cons:

• Must be done outside due to smoke and chaff

• Not a ‘set and forget’ method

• More difficult to precisely reproduce results at every roast

• Requires separate cooling method

• Difficult to monitor roast temperature

• Requires holding the heatgun and stirring for 10-15 minutes

• Quality of results dependent on operator technique  

The equipment essentials

The heatgun

The most important piece of equipment for this method is the heatgun.  For those unsure of what a heatgun is, think of a handheld hair dryer capable of reaching temperatures of 250-1100 degrees and powered by electricity.  Heatguns are commonly used for stripping paint, bending plastic, plumbing, electronics assembly, arts and crafts and can be found in the paint department of most hardware stores.  Heatgun prices typically range from $ 25 for light-duty home use models to $ 175 for industrial models. 

Work is still ongoing to find which models of heatgun are suitable for coffee roasting.  Makita, Wagner and Milwaukee models have been popular choices to date.  Preliminary data from user reports indicates that the heatgun should be capable of at least 500 degrees Fahrenheit and have an air velocity of at least 14 cubic feet per minute (CFM) in order to achieve sufficient heat transfer to reach roasting temperatures.  The higher the wattage of the heatgun, the more efficient it is for roasting.  Some users report that an adjustable temperature allows them to better ramp the roasts.   A cool setting may be useful to both cool the beans and prolong the life of the heating element.

At this time, the following models have been used with success:

Makita 1100

250-1100 degrees

8-14 CFM

1500 watts

$ 75 

Wagner HT 775\Milwaukee 750

500-750 degrees

19-23 CFM

1680 watts

$ 60

Wagner HT 1000

750-1000 degrees

CFM unknown

1200 watts

$ 30

Milwaukee 1220HS

750-1200 degrees

CFM unknown

1200 watts

$ 25  

Miscellaneous issues on heatguns 

One user felt that the Porter-Cable heavy duty heatgun had too high an air velocity (27 CFM) and blew too many beans out of the roasting vessel.   Two other users reported that using a heatgun with a maximum temperature of 450 degrees used for arts and crafts was not hot enough to reach roasting temperatures.  Another user reported that a special low-velocity heatgun (4-6 CFM) used for electronic assembly had insufficient air velocity to transfer heat to the coffee beans and they could not reach roasting temperatures.

The roasting vessel

The original roasting vessel used in this method is a stainless steel dogbowl, but other bowls and containers are used as well.  Many users have reported success using mixing bowls, saucepans or a round cake pan.  Some users have also used a metal mesh strainer or colander as a roasting vessel.

The most commonly-used type of dogbowl (the classic) looks like this in cross-section:  \_____/.  Here are some pictures of classic dogbowls:  

Another type of dogbowl (the non-tip or non-skid version) looks like this in cross-section:  /\_______/\.  This type of dogbowl is recommended if you use a BBQ grill as a supplemental heat source.  This is described later in the primer.  Here is a picture of a non-tip\non-skid dogbowl:  

A key element of success in this roasting method is to match the size of the vessel with the batch size.  If the vessel is too small, the depth of the bean mass will be too great, and an uneven roast and spillage will occur.  If the vessel is too large, the depth of the bean mass will be too shallow, and the surface area of the bean mass too large, leading to difficulty in reaching roasting temperatures, overly-long roasts and uneven roasts.  There is a ‘sweet spot’ of bean mass surface area and depth that will retain heat to sustain an endothermic reaction and reach first and second crack in an appropriate amount of time.  No matter what diameter is the roasting vessel, it should be at least 2.5-3.0 inches deep to avoid blowing the beans out of the vessel.  The recommended shape is round, so that beans do not get trapped into corners and roast unevenly. 

Recommended sizes depend upon the batch size and the diameter and depth of the roasting vessel.  A good rule of thumb would be to use a vessel with a capacity at least four times the volume of green beans used.  Using a classic dogbowl as a typical example, a 32 oz. bowl accommodates one cup of beans by volume; a 64 oz. bowl accommodates two cups; and a 96 oz. bowl accommodates three cups.  Although weight per cup is only approximate and depends upon the specific bean type, a good approximation is one level cup by volume weighs on average 5-5.3 oz., two cups by volume weighs on average 10-11 oz., and three cups by volume weighs on average 15-16 oz.  

The material of the vessel is important too.  It has to be heat-resistant, have a smooth interior surface, easy to clean and not subtract too much thermal energy from the bean mass.  Using cast-iron, heavy-gauge metal cookware or cookware with a clad or sandwich metal-core bottom can create hot and cold spots.  The mass of the metal acts as a heat sink to absorb heat unevenly resulting in prolonged and uneven roasts.   It is not known at this time if a glass, Pyrex or ceramic vessel would give satisfactory results or be safe to use.  Stainless or carbon steel or aluminum would be good materials for a roasting vessel.  If you are using a saucepan or cake pan, make sure the pan is uncoated, since some non-stick materials will not tolerate the high heat of a heatgun and may release toxic fumes.

For all of these reasons, and cost, a stainless steel dogbowl, mixing bowl, cake pan or saucepan is recommended.  These items may already be in your home or can be purchased very cheaply at thrift, discount, pet or department stores.  As an example, at a national chain of pet stores, a 32 oz. dogbowl sold for $ 5.49, a 64 oz. dogbowl sold for $ 6.99 and a 96 oz. dogbowl sold for $ 8.99. 

Stirring utensil

A heatproof stirring utensil can be used to stir the bean mass throughout the roast.  A long wooden or metal spoon or length of doweling works well.

Technique

A sample roast is presented here using a Wagner HT 775 heatgun and a 64 oz. classic dogbowl.  Of course, other types of heatguns and roasting vessels can work equally well.  This description presumes you have some experience with roasting.

Begin by assembling all the equipment and pour two cups (by volume, approximately 10-11 oz. by weight) green coffee beans into the bowl.  The sample roast shown here is Liquid Amber from SweetMaria’s.

Outside the house or in a covered and very well-ventilated area (this method does produce copious amounts of chaff and roasting smoke), put the dogbowl on a heatproof surface, start up the heatgun on the low setting (side louvers open at 500 degrees), and holding the muzzle of the gun approximately 1.0 -1.5 inches from the surface of the beans, begin playing the heated air evenly over the surface of the beans.    

If the airflow of the heatgun is not sufficient to stir the beans, then periodically stir the beans with a heatproof utensil while continuing to play the heatgun over the surface of the beans.  After approximately four to six minutes, the beans will begin to smell grassy and turn a light tan in color.  

Close the side louvers of the heatgun (changing the temperature to 750 degrees) and move the heatgun muzzle to within approximately 0.5 to 1.0 inches from the surface of the beans and continue playing the heated air over the surface of the bean mass.  As the roast progresses and the beans become lighter, you will often be able to stir the beans solely by the airflow of the heatgun.  Be sure to stir the beans throughout the roast.  Do not be alarmed if chaff blows off the surface of the beans and catches fire.  It will quickly self-extinguish.  Move the muzzle closer or further from the surface of the bean mass as dictated by how fast the roast is progressing.

At approximately 8 minutes or so, you should reach first crack, and second crack at about 9 minutes.   When the roast is complete to your liking, quickly dump the beans into a metal colander or cool the beans in the usual fashion.  This technique should give you approximately three cups by volume of roasted beans.  If the heatgun has a 'cool' setting, turn the heatgun to cool and let it run for a few minutes until it is cool to the touch.  This will extend the life of the heating element in the heatgun.  

The time to complete a roast also varies by volume; a one cup roast typically takes about seven minutes, a two cup roast typically takes about ten minutes and a three cup roast typically takes about 13-15 minutes (these times do not include cooling).  These times are also a function of this author’s roasting experience and preference: I like a slower and ramped roast to replicate a drum roast profile.  Other people who prefer a brighter roast, like those produced by poppers or the FreshRoast, may like to do a two cup roast in five or six minutes.  Decaf coffees will generally roast in less time for the same volume of coffee.

The total time is very dependent on volume, heatgun used, the roasting vessel used, ambient temperature and operator technique. If you are roasting in very cold temperatures, the roast time may be prolonged or you may want to put the roasting vessel into a heatproof box, tall stockpot or other container to help retain the heat.  The best guide to the roasting process will be your eyes and ears as you monitor the roast.

Another technique adopted by some users is to use a gas-fueled BBQ grill to serve as another source of heat during the roast.  A non-skid/non-tip dogbowl is commonly used since the skirt acts to retain heat under the bowl surface.  The BBQ is lit, generally set on medium and allowed to pre-heat for a few minutes.  The dogbowl with beans is set on the grill and the heatgun is used in the typical fashion.  Proponents of this method feel that the grill allows for a more controlled roast and more reproducible results. 

Conclusion:

Heatgun/dogbowl roasting is a quick, simple, and inexpensive way to produce quality roasted coffee.  The entry costs are low and the method very forgiving.  This is one of the most cost-effective ways to roast significant quantities of coffee for home use. 

Further resources:

The Home Roasting Talk forum at www.coffeegeek.com and “Home Coffee Roasting” by Kenneth Davids are excellent sources of information on roasting coffee in general. 

Contact the author:

If you have any suggestions or changes you'd like to see in this document, please contact the author, Michael Lloyd, at millcreek2000@hotmail.com