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Filtering smoke - bubbling smoke through water?

Discussion in 'Smoker Builds' started by gasbag, Sep 21, 2015.

  1. I have a DIY query regarding the bubbling/filtering of smoke though water.

    Take a look at the following image, just as a start guide:


    If a set-up was made using steel (iron) pipes similar to what's shown, where the left-hand vertical pipe was sealed and filled with wood chips, but instead of using an external air-blowing source (shown as an aquarium air pump) - an external heat source was applied to the bottom of the vertical pipe on the left (e.g. burner, or hot coals)....would enough "smoke pressure" be built up so that the smoke would be forced to bubble it's way out through the water?  If so, would the water have any effect at trapping some of the tar and creosote bubbling through it?

    But overall, the main issue is whether or not enough pressure would be built up by the external heat source, where they only way out for the smoke is through the water.  I can guarantee that a high degree of heat and smoke would be built up within the left-hand pipe.

    The other query is the same filtering concept, but instead of water....having the secondary vertical pipe (on the right, with the opening at the bottom) filled with some sort of steel wool - either fine steel wool or coarse stainless steel wool.  Would this have any filtering effect at all?

    My apologies if I was clumsy and confusing at explaining this.  I don't know if anyone can help me here, but I'm hoping someone might be able to help.

    On a side note, some commercial cold smoking businesses do use this idea of filtering smoke through water.

    Thanks all.
  2. smokin phil

    smokin phil Smoking Fanatic

    OK, zero background in any of this, so just my opinions. You will not build up any real smoke pressure. I also think that as well as some of the bad stuff, water would "filter" out the good stuff. A hot fire is all it takes to prevent creosote.

    Any idea what type system the big boys use? Ideas could be gleaned from there.
  3. Thanks for your reply Phil - much appreciated.

    Hot fire = no creosote.  Well understood, but a strong bed of coals is not an option for me - I'm mainly querying into cold smoking, where a two chamber rig isn't an option at the moment.  Down the track I may very well look into a two chamber rig, but not at the moment.

    What do the big boys use?  I'm willing to bet they're keeping that trade secret tightly wrapped, but I have come across a number of them.  One of them is below:


    "We produce our pure smoke by burning woodchips at the lowest possible temperature and force filter the smoke through a water bath to reduce potentially harmful creosote buildup on our products"

    What I would like to know is whether or not any of the venturi-style smokers have flexible steel exhaust smoke tubes, and/or flexible steel tubes can be fitted to them?  Also, has anyone used a venturi-style smoker, where they've initiated the "burn" at the top?  This would produce a slower rate of smoke production.
  4. mummel

    mummel Master of the Pit

    I wonder if it will carry the flavor?  I guess so.  Hookah's work really well and take out the bad stuff.  Im curious to see where this thread goes.
  5. nevrsummr

    nevrsummr Meat Mopper

    I'm sorry to see this thread hasn't received more ideas. With some of the brains on here they could really create some neat things if used together. I was going to start a new thread but decided I should search first and found this one.

    I have read about some fiberglass smoke filters as well. All intriguing to me.

    So far I have never had bad smoke or creosote problems. However I am thinking of building a smoke generator and am interested in incorporating some kind of filter as well as possibly a cooler into the system. I hadn't thought about water, but I like the idea. A major advantage I see is that the creosote would be easier to clean out.

    In the drawing I don't see why the smoke would be piped in from the top and vented out the bottom. That looks like a flaw imo. Obviously heat rises, so top venting is only going to help with removing unwanted heat, and also smoke/ other fumes.

    One time I pulled the chip pan out of the smoker because I didn't want any more smoke, about 30 minutes later I saw smoke coming out of the smoker, to my surprise it was coming off the pork butt, I think the sugars were burning. Yes, sure, probably my bad. But my point being bad fumes and smoke aren't always coming from just the wood. Even a dried out drip pan can create bad smoke. So for those reasons I think top venting is important.

    My questions would be:

    Are there characteristics of creosote that make it easy to filter from good smoke? For example particulate size? Weight? A temperature at which it doesn't rise, but may separate itself?

    By first understanding those keys, I think we will be well on our way to building a better smoker/generator.

    I have access to a lot of equipment, so if we start working out a design, I'm not afraid to build it. Or at least have it built.

    Exciting thread
  6. bill1

    bill1 Smoke Blower

    Yes, it's very much like a hookah pipe, isn't it!?!?   Here's my two cents...

    From what I google, hookah smoke is just as toxic as direct tobacco smoke, just cooler.  The major advantage of the hookah (to a smoker) besides the cooler inhalation is that the heat from the coals normally goes up, allowing the tobacco/shisha to last a little longer than a western pipe, ie  it's the human suction that causes the draft to reverse, accelerating the burning of the tobacco and drawing down through the water and out to the smoker.  (Plus it's more communal, but this Westerner thinks that's what brandy and cognac are for!)   

    So based on the health hazards of hookah, I don't think the desired smoke flavors for our meats would be lost bubbling them through water.  But it would result in a cold smoker even though the burning wood is close by.  (If you don't want to cold smoke, you could argue this wastes the heat you got from burning your wood you could use to cook meat.)  Now you could get the same cooling by passing the smoke through a very long pipe in air or though a shorter pipe in a pool of water, but that doesn't have the same coolness factor (no pun intended) to it as a "hookah-Q".  

    But there is the "water head"  pressure to overcome (pushing the smoke through the water) that's not in a real smokestack, so you'll need some air pressurization at the source (or suction at the end) to make the thing fly. Not sure an aquarium pump will do the trick.  

    If you're not burning anything in the far-right smoker box, it probably doesn't matter if you push the smoke down from the top or up from the bottom.  But if you want the option of cooking in there (e.g. with electric filaments) yes, you should use the natural draft and bring the smoke (even if cold from the water) in from the bottom and then out the top.  I also don't think you need the diffuser "shower head" that's shown either, just bring in one corner and out the opposite diagonal corner should give adequate uniformity.  

    As far as "creosote", or whatever you want to call the liquids and solids you get from smoke, it seems to me that they condense out from smoke at ~300-400F, so any distance you put from a smoke generator to your cooking chamber (which is at ~250degF) should be enough to keep it away from your food.  I suspect in the figure, it will happen BEFORE the water, so you'll have the problem of having to clean the gunk out of the pipes every few smokes.  Maybe super-thin-wall stainless piping leading to the water could stay hot enough that the stuff won't condense until right as it hits the water but I doubt it.   
  7. nevrsummr

    nevrsummr Meat Mopper

    Thanks for chipping in. Good info.
  8. tjones96761

    tjones96761 Newbie

    You could use a moonshiner's worm to cool the tubing from the outside. Make a copper coil and fit it in a bucket, then fill the bucket with ice water. It's going to make a pretty good mess inside the copper tube though. Make sure it's small enough you can get it in the sink or build an adapter so you can push hot water through it to wash it out.

    The problem is going to be friction loss due to resistance in the tube. Most people don't think "air" has friction loss, but it does. If you increase the tube diameter the resistance decreases, but it also decreases the surface area for the condensate and trash to stick to. The only other option is forcing the air to overcome the friction loss.

    I'm working on a forced air smoke box for my AMNPS. No unexpected hiccups yet. I was considering a cooling tower of some kind, but don't know if it will be necessary. At 35F ambient, the humidity in the air condenses inside the smoke box and I don't feel that I'm getting trash in the cook cabinet. That might change with a higher ambient and/or lower humidity. I'll get a thread put together and post separately once it's proven.
  9. bill1

    bill1 Smoke Blower

    Reading that salmon brochure a little more carefully did make me think a little more about this.  I'm beginning to think a major part of running the smoke through the water is to send it through a myriad of holes in the submerged pipe so you form a bunch of bubbles along with the liberated smoke.  So it's a way of hydrating the smoke.  Might be more effective at adding moisture in the smoking chamber than a water pan!  We can all argue whether water pans are good or bad, but there's no denying that moisture (steam) transfers heat (ie cooks) meat faster (at a given temperature) than dry air.  If you're smoking salmon or any product to make a living, you're going to want to send the product through the smoker as fast as possible so you want fast cook times.  Hence added hydration.  That also might explain why the smoke inlet to the smoking volume looks more like a shower head than a simple pipe.  
  10. bill1

    bill1 Smoke Blower

    The Cajun Express Smoker 


    is another smoker that blows smoke through water, but it's on the exhaust side where the back-pressure makes the device a bit of a pressure cooker. If anyone's familiar with them, could you tell us if what comes out of the water still smells smokey?  

    The mfgr refers to it as both a pressure regulator and a hydrator, so I think after it "burps" a bubble of smoke it inhales a little water into the smoker where it turns into steam.  
  11. I am trying for that "thin blue smoke", so don't want to introduce high volume air into my cold smoker producing a hotter fire and thicker, darker smoke..... Nor do I want to put the smoke output through a compressor or air pump that will end up clogging from the creosote.... So, my dilemma is how to create enough air pressure to force the smoke to bubble in a liquid....
  12. I just came across this discussion topic and although it's older I may have an idea for you . In my line of work as a mechanical contractor which we do , plumbing, fire protection, HVAC, gas etc... in a few specialized jobs if done, we have installed what they call air scrubbers/ filters for chemical exhausting. These are basically fine water misters that are installed inline on the exhaust duct that filters out the chemicals in the exhaust air coming from the buildings chemical work tables and other confined areas of chemical handling. My thought would be that by installing a small misting system before smoke enters the smoker it would cool the smoke and possibly take out any creosote . For cooling the smoke your water would have to be colder and not sure if you could recycle it over and over possibly through a chiller and filter , getting a bit complex. Food for thought.
  13. Being familiar with only basic of physics science I would think that for filtering system to work as shown in your picture you will need additional splitter air line from aquarium pump and venturi rig on pipe between first filtering cylinder and smoking chamber....diffuser close to the bottom of the smoking chamber and smoke exhaust on top of the smoking chamber..
    Last edited: Mar 15, 2019 at 8:13 AM
  14. bill1

    bill1 Smoke Blower

    Pressure and flow are two different things. If you want to submerge the outlet of your closed smoke source (burning pellets in a pipe come to mind) 6" in water, you have to overcome the pressure head associated with 6" of water, which is about a quarter psig. Doesn't sound like much but I doubt an aquarium pump on the inlet to the otherwise-sealed smoke source will do the job and certainly natural draft of any reasonable length won't. But a powered tire pump certainly will. (In fact, make sure you have some pressure relief valves in this system that you completely understand and have properly sized or you'll be making a bomb instead of bbq.) That's the pressure part. Your flow will determine how fast you burn your wood fuel and thus how much smoke you make. One of the posters didn't want excessive smoke so the flow rate of a tire pump should satisfy.

    I was initially skeptical about blowing smoke through water because I thought all you'd do is filter out all the flavorful things in the smoke. But I'm not so sure, so if someone wants to try it I'd love to hear the results. At the least, this may be a way to smoke liquids like sauces and soups. (I don't think smoked water would be a thing worth striving for.) I'd be curious how the flavor profile differed from just adding a good-quality liquid smoke.

    I've had good results injecting a (normal, unpressurized) smoke source directly over a steam source (water pan with hot water heater element). The steam carries the smoke to the meat imparting flavor at at least a comparable rate as dry smoke (the surface area to volume ratio of a steam droplet is huge), and the rate of cooking (power transfer) is immensely increased with steam--powers right through any "stall" associated with large cuts. (So the trick is optimizing at what temperatures to add the water and when to actively start generating steam.) And although there are some electrical safety issues to deal with, at least nothing's pressurized.
  15. bill1

    bill1 Smoke Blower

    Actually smoked water is exactly what liquid smoke is. The LS Wikipedia article says liquid smoke really caught on with the commercialization of the charcoal industry--it was a free by-product. There, nothing needs to be pressurized, just let moisture in a tube with smoke condense on the walls and drip down. Apparently Alton Brown made some of his own in one episode.