Smoke quality and smoke generation

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Smoking Fanatic
Original poster
★ Lifetime Premier ★
Jun 4, 2012
Central Wyoming
Howdy everyone.

I've been messing with my MES 40 over the last couple of months, mainly to get reliable burning of pellets in my AMNPS inside of the smoker itself.

I live at about 5300 feet elevation, and had been experiencing problems with the pellets going out mid-smoke, especially when the weather was humid.  I've got all of that fixed now using a few tweaks to the MES and my procedure.

Briefly, I'm piling the pellets in very deep in the AMNPS to get a larger cross-section of pellets, which seems to keep things going.  Plus, I removed the entire factory smoke generator and put in some baffling, etc., to direct the incoming air towards the location of the AMNPS.  This has made my burns 100% reliable, even at this elevation, and even when the humidity is nearly 100% (as in raining while I'm smoking).

But I got me a mailbox and some ductwork, etc., and have been thinking a lot about how to best implement a separate smoke generator chamber and smoke condenser/cooler setup to get better quality smoke.  The emphasis I see in all of the posts about building such setups is on cooling the smoke (very good for cold smoking, of course) and on condensing out what we presume are components of the smoke that have a lower boiling point. and capturing these "bad" things before they reach the product chamber.

And that all makes sense to me, but I also keep thinking about the subtle differences caused by humidity, temperature, elevation, air flow, etc., on how pellets burn for people at different times and in different places, and how these "combustion variables" affect the production of the smoke in the first place.

I feel that conditioning and "cleaning" the smoke can obviously be important.  But I also want to explore how the original burning conditions affect the quality of the smoke that's produced, too.  Without controlling how the smoke is generated to begin with, we can't really know what needs to be done to that smoke later to make it ideal for smoking our food.  And since there are so many variables affecting how the wood burns for people, what works or is necessary for one situation may be completely wrong for another.  So different people have success with one setup, yet it might not work for another person.  Or someone might find that their setup works great one time, but not so great another because the weather is different, etc.

It seems to me that to get repeatable consistency in the quantity and quality of smoke being produced by any smoke generator, you'd have to hold all of the combustion variables constant.  And that's something I never can do since the temperature, humidity, and even barometric pressure all vary with the weather.  Not to mention the fact that the draft through the smoke generator and the product chamber varies greatly depending on the temperature of the smoker relative to the ambient temperature, etc.

There's a lot of emphasis on using long pipes and/or separate chambers to condense out larger smoke particles to condition the smoke before applying it to the product.  But I see little or no consideration of controlling the quality of the smoke being generated to begin with.  Something I read elsewhere talked about the flavor compounds in the smoke varying depending on combustion temperature.  They said that at higher combustion temperatures, some of the "good" flavor compounds get broken down into "bad" flavor compounds.  I found that to be interesting!

Also, we tend to use smoke color as an indicator.  And this makes sense because smoke consisting of tiny particles causes Rayleigh scattering, which scatters short wavelengths (blue) preferentially.  So blue smoke is composed of smaller particles.  And larger particles cause Mie scattering, which scatters all wavelengths of light equally, so the smoke looks white.  So we know that white smoke is composed of larger particles.

And people seem to find that smoke made up of only smaller particles is preferable for flavor.  That all makes sense.

But something occurred to me the other night, when doing a cold smoke:  I noticed that the smoke coming out of the top vent of the smoker was white.  Very white!  Also, the smoke in the product chamber of my MES also looked very white.  So I thought I was going to have some very strong, bad-tasting cheese out of the run.  And this white smoke is something I hadn't seen before with the same setup (but doing hot smokes).

But when I smelled the smoke coming out, it was not harsh, and, unlike most of the time even with thin blue smoke, I had to really put my face right into the smoke to get much of a smell of it.  And it seemed to dissipate very quickly as it left the exhaust stack on the chamber.  So here I had blatant white-looking smoke, but it was milder than the usual thin blue smoke I get when hot smoking!

Also, less pellets burned per hour than usual.  That makes sense because the draft through the smoker was a lot less due to the cold smoking.  No heat (other than from the AMNPS) in the smoker means very low draft, and that means lower airflow to the pellets, which means lower burning temperatures and slower burning.

Also, the slow flow through the smoker and lower temperatures of the walls, grates, and food means that more crud is being deposited out of the smoke onto the food and the chamber walls, grates, etc.  So I could be getting higher rates of deposition of nasty stuff onto the product, and what comes out of the stack is only "clean" smoke (using the product to clean it - which might be a very bad thing). 

So I wasn't sure what I'd end up with!  It might be nasty and creosote-ish, or it might be nice because of the low burning rate/temperature of the pellets to begin with.

But then another thing occurred to me:  The white color of the smoke inside of the MES and the smoke wafting out of the stack may not be due to large smoke particles at all!  Instead, because of the cool ambient temperature and the moisture coming off of the cheese, I might be seeing large particle size, but the smoke particles may be tiny, but have water condensed onto them.  So I was seeing water droplets, not just smoke particles!

Bear with me - this is kind of technical, but it's fun and important, I think:

There are some great physics lectures by Walter Lewin on YouTube, and I've watched a lot of them.  In some of them, he does a demonstration of Rayleigh versus Mie scattering by showing that the smoke coming off the ends of some smoldering cigarettes is very obviously blue-looking.  It scatters the blue wavelengths of a white light source.  Then he does something interesting.

He sucks in a huge puff off of three or four cigarettes at once.  And he holds the smoke in his lungs for a fairly long time.  Then, when he exhales that smoke, you see that it's dramatically white!  It scatters all wavelengths of light!  So we know the particles are much larger than the original cigarette smoke.  Why is this?

It's because the moisture from his lungs has condensed onto the small smoke particles (using them as nucleation sites), and the resulting water droplets (surrounding the tiny smoke particles) are quite large, thus, they scatter all wavelengths and look very white.

This is how the smoke in my smoker (and coming out of the vent stack) looked.  Very white, yet dissipating rapidly as if I was seeing a steam cloud evaporate and vanish.

One of the classic things Professor Lewin explains in that lecture is why the sky is blue and clouds are white.

The sky is blue because most of the scattering of light is Rayleigh scattering caused by very tiny particles or even large molecules in the atmosphere.  Sunlight (white) light passes through the atmosphere and more blue light is scattered, and that's what we see when we look up at the sky.  Scattered blue light from tiny particles in the earth's atmosphere.

But clouds, on the other hand, are droplets of water that have condensed onto tiny dust or smoke particles.  The dust or smoke particles act as nucleation sites for water vapor to condense on, and we get clouds of water droplets, each one with a very tiny particle of dust or smoke inside.  And clouds look white because these relatively large water droplets cause Mie scattering, and scatter all wavelengths of light.

So, for us, the point is that when we see white "smoke", it may or may not be entirely smoke!  If you have the right conditions, what you may be seeing is water vapor that has condensed onto our smoke particles, forming a cloud of relatively large water droplets.

This is going to happen when conditions are right.  Kind of like seeing one's breath.

When we exhale, that warm, very moist air comes out of our lungs.  If it's warm and dry outside, that water vapor does not condense.  It remains as a vapor, and we cannot see it.

But if it's cool and moist (high relative humidity, at least) then we have a high chance of seeing our breath because as our warm, moist breath cools, the water vapor drops below the "dew point" for those conditions, and condenses into a visible cloud.

As it turned out, the cheese seems to have come out nice.  I let it all rest, on racks, for about 20 hours at room temperature, enclosed in a large trash bag that wasn't allowed to touch it, but which somewhat contained the moisture and didn't let the cheese dry out as it rested.  I then vacuum bagged all of it except one stick of string cheese.  I couldn't resist trying it. 

And lo and behold, even though I had smoked it with the AMNPS in the product chamber, for three hours, and had observed ominous "white smoke" the whole time, it actually tasted very good despite having not been aged at all other than the 20 hours or so of room-temperature resting.  So I was pleasantly surprised!  I guess the real test will be what it's like after aging for a few weeks.  My wife will be a good judge of that because she usually prefers a milder smoke flavor than I do.  Who knows?

Anyhow, this all adds to my desire to study the combustion variables with regard to the generation of smoke, as well as methods to "clean up" smoke once it's been generated.

It may be that at high elevation, with low temperatures and low airflow, the pellets burn slowly and at a low temperature, and you don't get much of the bad-tasting smoke components to begin with.  And thus, despite the white appearance of the "smoke", and the fact that no "cleaning" of the smoke was done, I still ended up with tasty smoke.

But what the control system and lab instrument designer in me longs for is to design a system that generates smoke in a repeatable and consistent way to begin with, and then study the characteristics of smoke generated under different combustion situations.  And then, if possible, come up with a setup that lets me get good and consistent smoke for hot and cold smoking.  Conditioning the smoke after it's generated may be one vital step to achieve what I want.  But I still want the original smoke generation to be consistent so that after the conditioning, I'll end up with the same kind of smoke every time, regardless of the weather here and the temperature of the product chamber.

And I also think about how the conditioning of the smoke will also be affected by ambient weather conditions, too.  If it's hot outside, the walls of any condensing pipe will be hot, and won't cool and condense the smoke the same as it would if it was cold outside.  So the smoke conditioning system really ought to be kept constant, too.

I know that all of this may be seen as going too far.  And I appreciate that most of us get good smoking without paying too much attention to all of the details.  We tinker until we come up with something that works well for us, and we learn what to do to adjust for varying conditions through trial and error.  I have gotten great food out of my smokers pretty much all of the time thanks to using a lot of the tips, techniques, and recipes everyone on this forum posts.

I'm just tossing out some ideas that I'd like to explore a bit.  I love smoking and eating the products.  But I'm also a die-hard tinkerer, so that's the spirit in which I'm thinking about all of this.  If it isn't fun, then that's no good!  :)

So I want to try to do some things to make all of this process more consistent.  And I'd be curious what all of you do to try to make your smoking more consistent and repeatable despite varying weather, etc.

It gets up to 100°F here in the summer, and down to -40°F in the winter.  Sometimes we have high winds (70 MPH gusts are not uncommon here in winter) and sometimes it's dead calm.  The humidity can be low (in the single digits) or high (100%).    Of course, I could just reserve smoking for only times when the weather is the same, but where's the fun in that?  ;)