Well it has finally come to this! Doing the math. I HATE math. As a visual thinker, it is not my strong suit even if I did well in college math courses. Math does have its place , though. I’ve been wondering for quite a while what the size of the roasting vessel will need to be for a capacity of 15kg (33lbs) of green coffee per batch. Solid geometry is the easiest way to figure it out.
Part 1 – Density of Coffee
When coffee is roasted, the density of the bean decreases substantially. First of all, many components vaporize (in the case of silver skin, separate) and go out the exhaust stack. Secondly, as the water in the cells turns to steam, the cells inflate and the whole bean grows in size much like popcorn. The weight goes down and the volume goes up, therefore density is reduced and the space need to contain the beans increases. The darker one roasts the beans, the lower the density becomes. That’s why French Roast makes the bag look much fuller or is packaged in a 12oz. bag when Full City Roast fits fine in a 16oz. bag.
We are really concerned, then, with the least dense coffee to determine the roasting vessel size. I don’t plan on roasting beyond a French Roast, so I decided to measure the density of a good French Roast as a benchmark. I weighed 500ml of Mr. Espresso French Roast and found that it weighs 158gr net. Note that it probably lost 18% of the original green weigh for this degree of roast. If you do the math, the volume that 1kg of this French Roast requires to contain it is 3,200cc. This means that 15kg of the French Roasts requires 48,000cc or around 3,000 cubic inches of space to contain the beans.
Part 2 – Sizing of a Bowl
There are many shapes of bowls that can contain the beans. I have focused for the moment on truly spherical bowls. You could have a shallow, wide bowl. You could have a bowl that is essentially half of a sphere (the deepest one possible). I suspect that the half sphere is not ideal in that airflow and agitation might be problematic. Excessively shallow bowls would have to be very wide, which is impractical. Some balance of depth and diameter will have to be arrived at. I did three tables of calculations for spheres. One at 50,000cc volume (solid with beans), 60,000cc which allows for 20% agitation and head space, and 75,000cc which allows for 50% agitation space and head space. The calculations are in the table below.
Assuming the the 75,000cc model is a good one, we can see that the bowl size varies from 8″ deep and 52″ in diameter to a 1/2 sphere of 26″ diameter and 13″ deep. A 10″ deep bowl is about 3′ in diameter. All of these seem to be within the range of size that would be appropriate in a shop setting.
Part 3- Sizing of a Drum
The drum is a fairly simple geometry, yet there are the two variables: length and diameter. For any given volume you could have a short, large diameter drum. You could have a drum that is essentially a long tube. Drums that are too short or too long will have problems with even heating, agitation and ability to quickly evacuate the drum at the end of the roasting process. Some balance of length and diameter will have to be arrived at here, as well. I did three tables of calculations for drums. One at 50,000cc volume (solid with beans), 60,000cc which allows for 20% agitation and head space, and 75,000cc which allows for 50% agitation space and head space. The calculations are in the table below.
I have marked in pink the values that do not make sense. The drum is either too short or too long. If 75,000cc is a good value, then drums in the range of 22″ long and 16″ diameter to 34″ long and 13″ in diameter seem appropriate. Again, these are sizes that would fit will in a shop environment.
One roaster geometry that has intrigued me is a bowl. While there are no shop scale roasters that use the bowl geometry, there is at least one large scale roaster that uses a modified bowl approach. The basic idea is to use a spinning bowl to throw the beans up the sides using centrifugal force. The beans then tumble back down to the center. In addition, the spinning action creates a swirl along the spin axis that further helps agitate the beans for uniform roasting.
I’ve been thinking about the use of a perforated bowl and a solid bowl. The perforated bowl allows for convective heat transfer via heated air blown through the holes and additional agitation of the beans by forcing them off of the surface of the bowl. The solid bowl is better for being able to independently heat the bowl for conductive heat transfer.
The first sketches I’ve been working on are some thumbnail sketches of possible airflow schemes. The airflow path in a roaster is of critical importance, since the majority of the heat transfer is done via convective heat transfer. While there are other variations, the sketch below shows five of the schemes that seem most promising to me.
The Sketches Analyzed
Sketch “A” is characterized by a central down vent. The heated air enters through the holes in the perforated bowl, helping to agitate the beans. It then flows down a central vent to evacuate chaff. When the roast is completed, the central duct is moved in such a way (by dropping or being lifted) as to suck down the beans into the cooling chamber. The bowl can be heated by a shielded burner to give adjustable conductive heat transfer. Advantages: for a sample roaster can have a glass top to watch the whole process, has some great cooling system possibilities. Disadvantages: complexity of the bearing system since the central vent is cylindrical and active, rather than a simple shaft.
Sketch “B” is characterized by bowl perforation supplied air and peripheral sidewall vents. The heated air enters through the holes in the perforated bowl, helping to agitate the beans. It then flows upward to the top of the bowl wall to evacuate chaff. When the roast is completed, bowl would either need to be tilted to dump out the beans or some sort of bottom door opened to allow the beans to fall into a cooling chamber. The bowl can be heated by a shielded burner to give adjustable conductive heat transfer. Advantages: a simple layout for the bearings and support system. Disadvantages: Cooling system is made more difficult to access.
Sketch “C” is characterized by bowl perforation supplied air and peripheral trough vent. The heated air enters through the holes in the perforated bowl, helping to agitate the beans. It then flows over the rim and into a vent trough to evacuate chaff. When the roast is completed, the bowl speed could be increased to spin the beans out into the trough and directed into the cooling chamber (this would require the bowl to be more shallow). The bowl can be heated by a shielded burner to give adjustable conductive heat transfer. Advantages: a simple layout for the bearings and support system, simplified cooling system. Disadvantages: Beans falling into the trough during the roasting process.
Sketch “D” is characterized by bowl perforation supplied air and an overhead vent. The heated air enters through the holes in the perforated bowl, helping to agitate the beans. It then flows upward to the top of the roasting chamber to evacuate chaff. When the roast is completed, bowl would either need to be tilted to dump out the beans or some sort of bottom door opened to allow the beans to fall into a cooling chamber. The bowl can be heated by a shielded burner to give adjustable conductive heat transfer. Advantages: higher capacity for the system, simplified ducting, simple layout for the bearings and support system. Disadvantages: Cooling system is made more difficult to access.
Sketch “E” is characterized by overhead duct supplied air and peripheral side vents. The heated air enters through an overhead duct in a relatively high velocity, which further agitates the beans. It then flows through vents in the wall above the bowl to evacuate chaff. When the roast is completed, bowl would either need to be tilted to dump out the beans or some sort of bottom door opened to allow the beans to fall into a cooling chamber. The bowl can be heated directly with a burner to give adjustable conductive heat transfer. Advantages: higher capacity for the system, simplified ducting, simple layout for the bearings and support system, potential for very high convective heat transfer. Disadvantages: Cooling system is made more difficult to access.
In previous posts on tasting coffee, I have not mentioned what is to me the most important aspect of taste: it is situational. The taste of a beverage is inexorably linked to the situation (context) within which it is partaken. One’s mood, foreknowledge, sights, sounds, aromas, drinkware, and the people we are with all greatly influence how something tastes. That is why the cupping room of good coffee roasters is stark and everything is done in a uniform way. By excluding or standardizing situational factors, it is hoped that the intrinsic flavor of the coffee will be discerned.
For the rest of us, the fact that taste is situational is not a problem. In fact, it can greatly increase our enjoyment of a beverage. Situational enjoyment can be broken down into two major groups: foreknowledge and surroundings. Foreknowledge is what one has be taught to expect, look for, or appreciate. For instance, if one goes to a coffee place that has a Yelp rating of 5 stars, one is preconditioned by foreknowledge that people “in the know” see it as heaven on earth. The coffee will taste better than in a generic white mug at the office. Similarly, if it is generally “known” that a certain restaurant has the best pizza, it will be more heavenly tasting than the same pizza served in a white box.
Surroundings are perhaps the most influential factor in taste. I find that taste experiences while traveling are heightened. Life, in general, is heightened in travel; being out of one’s element, hearing and seeing new things. The people you are with influence your thoughts on taste. If they all are swooning over a cappuccino… it must be good. The visualization of process also influences taste. When I was at Four Barrel Coffee in SF, seeing the roaster, all of the coffee equipment and various rituals of production definitely influenced my enjoyment of coffee. The wise coffeehouse owner will recognize the power of situation and intentionally design a situation favorable to enhanced taste.
An Illustration – The Best Wine Ever
At a recent dinner party, I asked a friend what was his fondest memory of wine or what was the best wine he had every enjoyed. The story began flowing immediately. He and his wife had reservations at the French Laundry. They determined that they were going to fully enjoy their meal, so they ordered a very expensive Bordeaux. He related in great detail, the remarkable lineup of small courses, the gracious service, and the stellar wine. For him, it was the very best wine experience ever.
The best wine I have ever had (and wine memory) was a $9 bottle of Villa Cornarea Arneis drunk on Father’s Day 2007. We were staying in the hilltop guesthouse of Villa Cornarea (just outside of Alba, Italy) with vineyards of Arneis grapes sloping down on all sides. Cindy and our two sons had rented vespas and were touring the Barolo region that day. On our way back we were on steep switchbacks in the forest. We looked back and Cindy was gone. In a state of panic, we turned back and I saw a glimpse of a car stopped and a scooter down on the side of the road — I thought the worst. Thankfully she was just scraped up and some italian men had stopped to help her! Such relief. We continued on with me riding her damaged vespa. About 10 miles from the village of Canale, we arrived at a 
roundabout and headed into it with big trucks speeding our way. In the lead, I decided to take an exit that would be longer travel time, but safer. We all made it — except for our youngest son, who continued down the main highway! So I took off after him. After much angst , we were finally reunited.
Late in the afternoon, with no one at the Villa Cornarea but us, we opened a bottle of their Arneis, ate breadsticks, and smoked cigars as the sun set over the vine covered hills. It is a great wine, but heightened by fear of death and loss, thankfulness for a great outcome, and being right where the grapes are grown and wine produced, it was a rapturous wine.
In comparing our two stories, I think that my friend was primarily affected by foreknowledge of the reputation of French Laundry and of expensive Bordeaux. For us, there was the foreknowledge of being at Villa Cornarea, but it was mainly situational. Even the situational part had a large fraction of emotion as the element that enhanced taste way beyond the normal.
As Warren Zevon said: “Enjoy every sandwich”. Enjoy the moment; enjoy the situation you are in as you partake.
I’ve been wanting to visit Cortez Coffee for sometime. Ron Cortez, the owner, must have the largest collection of commercial roasters in one location in Arizona. He has everything from a 1lb roaster to a 40kg roaster and all sizes in between. It is always interesting to see what the current range of commercial roasters looks like and to examine details such as motors, burners, controls, etc. Lewis Berman, one of my collaborators, joined me to check them all out.
After a bit of jovial chat with Ron, he took us to the rear of his roasting plant to look at his small Ambex roasters. Ron selects which roaster to use based upon the size of a particular order. Since roasters have a limited operating range for proper roasting with partial batches, he chooses the roaster that will be in the proper operating range relative to maximum capacity. The smallest Ambex is a YM-2 (2kg max) and the larger one is a YM-10 (10kg max). Both are pretty conventional drum roasters that use atmospheric gas burners. Ron, said that they are basically Toper roasters (made in Turkey) which are then modified/assembled by Ambex. By the way, Ambex has some great articles on roasting and, particularly, roast automation.
The next roaster we looked at is a Probat 12kg shop roaster. I always love looking at Probat roasters. The Germans have a certain way of engineering equipment that I admire. This one is an old design, but has not been used, so it is immaculate. We peered in all of the access covers to see how the burners heated a transfer plate, rather than directly heating the drum. Lots of nice quality work throughout.
Ron’s largest roaster is a 1980’s vintage Vittoria from Spain. It is really a piece of art, which I couldn’t photograph very well in the space. First of all, both the drum housing and the cooling tray each sit on individual voluptuous pedestals. The designers did not resort to bulky housings to hide all of the workings. The hardware is beautifully crafted and the thing is built like a tank with very heavy castings. There are some interesting technical features: it is the only one of Ron’s roasters that has a perforated drum or a power burner. All of the others are a solid drum and have atmospheric burners. I really liked the airflow path in this roaster.
The roaster was in use while we were touring. The roasting technician was using some proprietary software that Ron has developed to run the roasting profile. At the proper time, he was alerted to dump the batch. I am always mesmerized watching the beans flow round and round in the cooling tray.
Ron Cortez is very proud of his operation. He’s formally been in the coffee business since the early 1990’s, but is from Costa Rica and his family was involved with coffee there. Ron is kind of a jack of all trades, cupping, repairing coffee equipment, experimenting with espresso machines, and generally thinking 24/7 about coffee. He is a gracious host and we appreciate the time he spent showing us around.
We then retired to Cartel Coffee Lab for a cappuccino and discussion. I pulled out my yellow pad and started sketching an idea I have for a centrifugal bowl roaster. Lewis was intrigued and asked me many questions that forced me to explain details that had just been floating around in my head. We were both pretty energized by the discussion (and caffeine). The overwhelming use of drums for roasting has pretty much influenced me to NOT use a drum, if another geometry will work as well or better. We left in the glow of a promising idea and plan to think about the details and discuss further.
My roasting philosophy is relatively simple. I respect the great difficulty and amount of labor that goes into the growing of great coffee. I come from a farming family and understand that it is a rather neglected part of the industrialized world. Hence, I will only buy top quality green coffee and pay a fair price to the farmer. The green coffee will be judged on its own merits with story stripped away.
I consider roasting both an art and a science. I believe that a roastmaster has the freedom to roast to his own taste using any coffee. Clearly there are roasting defects, such as baking, stalling, tipping, etc. which are never to be a part of a great coffee, but degree of roast and profiles are in the hands of the roastmaster. I look for balance, complexity and being true to type. Furthermore, I do not feel constrained by convention or trends. I am fine with darker roasts and lighter roasts, all dependent upon the coffee, its use, and my thoughts at the time.
Ultimately, I will roast to my palate alone. This is not, at its core, a commercial project. If people like my taste in coffee (and I hope they will), great! If they prefer something else, equally great! I do not claim to have the best palate or coffee: it is subjective, but I will do my very best.
All serious roasters of coffee have a written or unwritten philosophy of roasting. While amateur roasters may have so little experience and knowledge that they are essentially random experimenters in the craft, professionals have come to firm conclusions. The fundamental “truths” that govern a roasting philosophy differ greatly from roaster to roaster. I use the term “truths” to acknowledge that these are subjective truths rather than absolute truths. People can tend to become quite moralistic about subjective truth and this cause a host of problems. In this survey, I will point out some of the prevailing “truths” and the attendant roast philosophies.
Our Consumer is Price Driven
Roasters who have positioned themselves in this market segment hold as “truth” that their customer buys mainly on price, given acceptable quality. The roasting philosophy is “buy the least expensive coffee you can, then use fast high-yield roasting to a relatively light color and blend out defects as best you can”. Why? If cost is the driving force, you must start out with inexpensive coffee. During the roasting process, you want to minimize the weight loss during roasting (conventional roasting will result in a 13% to 18%) and the amount of energy consumed, hence roast times well under 5 minutes. This does have adverse effects on flavor development. Clever blending of poor coffees can then improve the overall flavor to the acceptable range. Sadly, this is probably the largest market segment for coffee in the US.
A poor country variant of this is to buy worse coffee yet at an even cheaper price and roast very darkly. As coffee is roasted more darkly, it loses many of its varietal characteristics which are replaced by roast flavors of carmelization. Dark roasting also roasts out many of the defects in very low quality coffee, making it more palatable. The reduction in weight due to dark roasting is offset by the lower price paid for inferior green coffee.
Our Customer is Looking for a Broad Selection of “Gourmet” Coffees at a Reasonable Price
This is a huge market segment, also. I use the word “gourmet” to indicate a nebulous term indicating some focus on quality and taste. Roasters who ascribe to this truth are generally larger, regional roasters and astute in business. The roasting philosophy is “we roast to customer preferences and source coffee and set roasting standards accordingly; however, we will not buy coffee below a certain quality level nor cut corners in roasting”. Such roasters offer a wide variety of varietal coffees and blends roasted to various degrees of roast. They would think nothing of doing a double French Roast, if there was a market for it. They are are fine with Fair Trade coffee, if there is a market for it. They are market driven. In roasting, they use high volume drum roasters (roast times in the 12-15 minute range) for the most part and most do not cut corners, such as water quenching (can pre-stale coffee and add back some of the weight-loss). Roasting is largely automated, but most have well qualified roasting teams and a QC lab. I would put Starbucks in the better end of this roaster group and Millstone Coffee as typical.
Quality First: Interventionist Variant
Roasters in this category believe that (1) always focusing on quality throughout the process, rather than price, is best and (2) the role of the roaster is to lend house style to the inherent characteristics of the green coffee. The roasting philosophy is “we focus in quality at all steps of the process; we see the role of our roastmaster as creating our signature coffee(s) from great green coffee”. Such a roaster will be exacting in the sourcing of green coffee, roast it meticulously, package it properly, and attempt to educate the consumer. They typically spend much time in research and experimentation to get the details right. They will roast reasonably darkly if they feel that balance and complexity are enhanced and consider the “input of the farmer” and the “input of the roastmaster” to be on equal terms. The best are similar to a Champagne house (link is to Bollinger, one of my favorites) where various wines are blended to end up with the “house style” or there may be a single vintage. One of the best roasters in this category is Illycaffe of Trieste, Italy. I recently asked them to tweet their roasting philosophy: “the most critical stage in our coffee production & we strive to achieve a balance between acidity & bitterness in each roast”. Another smaller firm is Mr. Espresso of Oakland, CA and their roasting philosophy tweet: “in one word: balance. old world verus new. tradition vs. progress. quality vs. growth. light vs. dark. fruit vs. choco.”
Quality First: Non-Interventionist Variant
Roasters in this category believe that (1) always focusing on quality throughout the process, rather than price, is best and (2) the role of the roaster is simply bring out the inherent characteristics of the green coffee. The roasting philosophy is “we focus in quality at all steps of the process; we see the role of our roastmaster as revealing the characteristics (expression) of great green coffee”. Much of what is done is identical to the Interventionist Variant, the main difference being that the goal of the roasting process is the revelation of the potential of a green coffee without adding roast induced caramelization and other roasted notes. The idea is that such notes mask or obliterate the underlying, more subtle notes. Balance is not a primary goal in the roasting process. One of the finest roasters in this group is George Howell of Terrior Coffee in Boston, MA. George was kind enough to tweet me his roasting philosophy: “bring out intrinsic flavor of each terroir and variety & allow each to speak w/o being smothered by caramel from roasting”.
Certainly one of life’s small pleasures is enjoying a great cup of coffee. The whole act of brewing the coffee starts to stimulate thought and memories. The noise of the grinder and the release of the aroma of freshly ground coffee, followed by brewing combine in a daily ritual that brings much comfort (children remember it vividly as they become adults). Then there is the steamy aroma rising from the cup as you take your first sip. Wow! What an incredible pleasure to be enjoyed as you continue with your cup. It is very much a right brain sort of experience: holistic and highly subjective.
Another way of looking at coffee is through a more left brain approach: logical, linear, analytical. In this case, one looks at the ritual of coffee making as a series of steps to be standardized and optimized for the perfect extraction. The tasting of the coffee is not as much for the pure enjoyment of the experience as it is to appreciate the subtle nuances. One thinks of flavor components in the coffee that remind them of other reference flavors and aromas, such a berries or citrus. Then the analysis of mouthfeel and finish come into play. Taking notes for future reference helps one remember a special coffee and what made it so. This is much more of an intellectual pursuit with satisfaction and respect for a coffee as a positive outcome.
So which is the better way? Both! Drinking coffee for the pure enjoyment of the beverage and the ritual is what has made coffee a popular beverage in the first place. Millions of farmers around the world would be growing something else if coffee were not an enjoyable beverage. Enjoying the creation and being thankful for it is an integral part of humanity. However, if no one were tasting in an analytical way, there would not be progress to improve quality, rather quality would slip as firms tried to offer maximum “enjoyment” at the lowest cost. This happened in the U.S. during the period of 1940-1990 when there was a “race to the bottom” on cost and , therefore, quality. The result was a steady decline in coffee consumption in the U.S. Thankfully, a dedicated group of individuals, many of whom are represented by the SCAA (Specialty Coffee Association of America), did take an analytical approach to coffee and reversed the trend. They cupped coffee very analytically to buy only the best green coffees and to encourage farmers and co-ops to improve growing and processing methods. They are to be commended for the much better state of coffee in our country today.
I would, however, suggest that one can over-analyze coffee: breaking it down into flavors and descriptors rather than enjoying the whole. If you are bound up in words and descriptors, try relaxing and simply enjoying coffee for the graciously given pleasure that it is. It is an amazingly enjoyable beverage! Be thankful for those who have put in so much time and effort on your behalf via analytical approaches to make sure you have access to great coffee.
Being a design engineer, there is a particular form of art that I have come to admire: patent and trademark illustration. It is a rather tightly defined sort of art — defined by the US Patent and Trademark Office in Section 1.84 of the Manual of Patent Examining Procedure. Line widths, margins, paper size, and numerous other standards are set forth. The basic idea is to create a legible, easily understood drawing that illustrates what the text of the patent describes verbally. Furthermore, the rules are intended to make black ink drawings (required) easily reproducible.
It is interesting that a certain artistic style developed that is common to patent illustrations that is not required by the rules. It is characterized by heavy lines, shading, flowing “pointer” lines, and certain font styles. The style is easy to recognize even when taken out of context. I happen to love the style. Reading the text of the patent, which is also in a very unusual format, combined with examining the drawings is a fun exercise for the inventive type.
Below is a detail view of a patent illustration by my great-grandfather, Herbert L. Johnston, for a mechanism for a commercial mixer…
This is the primary illustration of the invention, showing the patent date, number, and the signature of the inventor…
And this is the machine, itself at Liberty Market. It was built in 1934 and is currently used daily by Herbert’s great-great-grandson to make pizza dough…
I am reasonably please with progress on the roaster project for the month of January. As is always the case with “the first creation” part of the process, I have very little to show for it. No roaster, no experiments, no coffee… nothing tangible except for sketches, articles, and notes.
What I do have is a much better understanding of the scope of the project. I’ve learned plenty about areas that I don’t know and will need to know or subcontract. I’ve met several people and talked through ideas, which for me is always a way of refining ideas (I’m generally a verbal processing thinker). Writing the blog has helped in a similar way and I’ve enjoyed the feedback. The sort of roaster that seems best to me is starting to vaguely take shape.
Here is my laundry list of things I need to work on over the next couple of months.
1. Learn more about burners (power, ambient and infrared)
2. Learn more about high temperature blowers
3. Learn more about temperature sensors (contact and non-contact)
4. Examine sources for motors and variable speed drives
5. Learn more about Arduino, PID, and other possible control systems
6. Examine sources for linear actuators and stepper motors
7. Learn more about colorimetry, possibly visit Agtron
8. Examine sources for high temp bearings
9. Visit local machine shops and welding shops
10. Find local foundries and multi-axis water jetting shops
11. Build some sample roasters
12. Start interacting with green coffee brokers
13. Determine the necessity of getting UL approval and process
14. Study Victorian era detailing and Steampunk aesthetic
I had a great conversation with a gent who is a multi-talented fabricator/inventor about how to go about designing a machine. He proposed that once you have the basic idea, just start building. As you run into obstacles,simply make changes as you go. If the whole thing doesn’t work the way you want, you can further modify it or start from scratch. This approach is one that I have used successfully. Particularly in cooking, I often start with a basic idea or a couple of main ingredients. From there, I add and improvise until I have a final dish that I am proud of. Sometimes, the dish just does not work for me, so I just throw it out (remembering the problems for future experiments) and start over.
On the farm, we use this iterative approach frequently for problem solving. We have plenty of tools, inexpensive material, and generous tolerance for mistakes. Our irrigation systems and produce wash area are in a constant state of changing and upgrading, without a grand design drawn in detail at the start. We learn new information as we go and make the needed changes. It is a very effective design methodology for farm infrastructure. We do not have the time, allocated funds or sufficient knowledge at the inception to create a fully detailed grand design.
This approach is NOT how airliners are built. Yes, there is modeling of components and iterative design at some level, but that is not the primary way of designing aircraft. Aircraft are too complex, too expensive, and rely upon too many people to be left to a purely iterative build > correct > build > correct > build approach. A team of designers, engineers, and scientist apply knowledge, physics, chemistry, material science, CAD, and other disciplines to designing the complete aircraft and individual components before much fabrication takes place. It is designed, then built. Iterative design happens within that process.
So which way is best for the roaster project? It seems to me that a combination of the two basic approaches makes sense. For the sample roaster(s), it probably makes sense to do the build and correct iterative method. I will be using smaller amounts of inexpensive materials and very little subcontracting of components (making it in my shop). Futhermore, I do not know everything I would like to know and will need to learn during the construction of the devices. It is likely that the sample roaster(s) will catch fire, seize, warp, discolor and other unpleasant things. This will help me foresee problems as I correct them. One or more sample roaster will end up in the dumpster, I am certain.
Taking these results, my engineering education, plenty of thought, advice of others, and the technical skills of others, I will then design the roaster. The design will use fully detailed mechanical drawings (I will do them by hand) for most components. The design will incorporate an understanding of relative expansion of various materials, static and dynamic loading, thermodynamics and other disciplines. The drawings will then go to subcontractors for fabrication. This approach makes sense for the roaster because: I should have enough collective knowledge to do a complete design, mistakes will be much more expensive, there are many fabricators and components involved, the final product needs to be of top quality (longevity plus fit and finish) AND I it forces me to have considerable mental discipline.
