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Conical shape

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  • Conical shape

    I just would like to know what the difference/benefits of having a steeper cone on a fermenter as opposed to having a shallower cone are? Is is better fermentation, flavors, etc?

  • #2
    Primarily anything less then 60 degrees reduces yeast from settling in the bottom of the cone.
    I have read that overall tank geometry can attribute to different taste profiles from fermentation, but I don’t have a reference for details on tank geometry impact on fermentation.


    • #3
      Supposedly cylindro-conicals are supposed to lower overall ester production. The overall height-to-width ratio lowers the amount of the yeast exposed to oxygen, so having really tall, thin fermenters likely won't make for great ales, but would likely make some nice lagers

      Of course, you could just oxygenate often and it wouldn't matter either way...

      My vote would be short and wide cylindros with steep conicals if you're having some made.


      • #4

        Generally speaking the purpose of the cone on cylindoconicals is yeast collection and harvesting. They do of course impact some of the dynamics of fermentation, and hence flavor profile. I have some fermentors with a very shallow cone, and they really to not allow proper cropping of yeast as is possible with a proper 60* cone. If you plan on cropping your yeast from the cone stick with 60*. I don't have experience with anything steeper, though, just more shallow.

        Jolly Pumpkin Artisan Ales
        Last edited by Greenbrewmonkey; 12-09-2006, 10:33 AM. Reason: dyslexic


        • #5

          It doesn't have anything to do with oxygen, but rather the convection in a "pencil-shaped" tank. The convection allows for the yeast to have more access to the substrate (wort) which reduces ester production.


          • #6
            Originally posted by crassbrauer
            It doesn't have anything to do with oxygen, but rather the convection in a "pencil-shaped" tank. The convection allows for the yeast to have more access to the substrate (wort) which reduces ester production.
            Say you have a 1 to 1 ratio cylindro, the inside is essentially has even access to any non-dissolved oxygen sitting on top of the wort. Take a 2 to 1 ratio (taller, thinner cylindro) and the amount of wort you have that is in direct contact with the headspace goes down bigtime.

            Since we all know ales are top fermenting, it would take a pretty serious amount of convincing (and scientific data) to get me to believe that shape and oxygen don't have anything to do with it. Yes, that oxygen will be gone quickly, but so will dissolved oxygen in the wort, and yeast need both of them to be happy...especially in early fermentation!

            I agree with your convection assessment above, I just think that there's more to it than that
            Last edited by jason.koehler; 12-09-2006, 05:30 PM.


            • #7
              One word comes to mind from your question....”Pandora”.
              Some of this information is taking from a recent article in an international magazine.(plus my own thoughts)

              Designing and constructing Cylindroconical tanks, these days, as well as other types of tanks, comes down to scientific formula, which is based on acceptance from the brewing community and the quality of product coming from these tanks. Most of the hard work has been done over the last 30-40 years, where design and testing was carried out. Now it is up to you and the tank manufacturer (buyer and seller) to agree what is best for your needs.

              Some considerations are;

              In-house criteria.

              Are the tanks used for long storage of strong beers or low volume beers?

              Are you using a 1 tank process? (Uni tank, where beer is fermented and conditioned in one tank.)
              or a 2 tank process? (Beer is fermented in one tank and transferred to another for conditioning/ cooling)

              Tank size? Used for a single brew or multiple brews?

              Head space required - 25% for fermentation, 10 % for storage.

              Brewery space restrictions - height, weight, width.

              Cooling - propylene glycol, ammonia, cooling surface area.

              Cone cooling - cooling area and finish of interior to cool, settle and maintain temperature of yeast and/or beer.

              And the list goes on.......

              Design of 60 degree cones has been accepted throughout the industry but is not 100%. Different Cone angles have been constructed (for valid reasons)with acceptable results.
              But even among constructed 60 degree cones, result(final product) may vary. (One reason why blending is done)

              If I confused you....good. If you are planning on having tanks built that “vary from the norm”, have a good reason and the documentation, understanding why. Also, I would recommend having it done by a reputable manufacturer.( Buyer beware) There are a lot of excellent brewery manufacturers out there, but as in most cases, there are ones out there that should be... “drawn and quartered”. ( Sorry to say, I have dealt with the later on more then one occasion.)

              If you are buying used, again, but from a reputable seller who ask you the questions above and more, or... I have some ocean front property for sale in Montana you may be interested in.


              • #8
                Top-fermenting yeast rise to the top because they form little chains or groups of cells upon budding, whereas the bottom-fermenters don't; their daughter cells generally break off before too long. (This isn't describing why flocculation occurs – that's something different). Yeast increase their biomass primarily during the time that oxygen is available, because oxygen allows for a number of processes to occur which make it possible for the yeast to produce more cell structures (important among them is the lipid bi-layer of the cell membrane). Any oxygen present is taken up by the yeast pretty rapidly. Once this has taken place, fermentation gets going. Oxygen should not be present during fermentation, even during "early fermentation", especially if you have a closed tank. CO2 pushes top-fermenters in their little "chain gangs" to the top. It is produced only during fermentation. In fact, if you want to increase the esters in your beer, overpitch or underaerate, adjust your mash program so that you have more glucose in your wort or ferment in a horizontal tank.

                A couple of fluid dynamics researchers (Denk and Stern) figured out what happens in cylindro-conical tanks during fermentation. The gist of their research is: there's a lot more convection in a tall, narrow cylindro-conical tank than in a more evenly proportioned tank. This convection, which is produced by a long, oscillating, centrally-located column of CO2, carries the yeast with it and allows more homogenous contact between yeast and wort, which results in the production of fewer yeast by-products, even if the top-fermenters are banded together in their little groups.

                The partial pressure of the CO2 on the yeast at the bottom of a "pencil" fermenter may also play a role (see info about fermentation under pressure). It is thought that the increased partial pressure of the CO2 near the bottom inhibits the production of acetate ester.
                Last edited by crassbrauer; 12-10-2006, 07:13 AM.


                • #9
                  On the subject of O2 exposure in tanks of varying aspect ratios, I always figured that O2 IN SOLUTION played a much more significant role in fermentation than does surface O2.

                  The comparison that comes to mind is trying to force carbonate a batch using a stone at the bottom versus just applying CO2 at pressure pressure to the top.


                  • #10
                    forgot something

                    In my little list above for increasing the esters in beer, I see that I forgot to write "increase the fermentation temperature".


                    • #11
                      Looking at the initial question, which seems to be refering to tanks of the same size, just different cone angles...

                      Most important is how cleanly your yeast can be harvested. I had a 45 degree JV tank which was only OK for getting a decent harvest, but racking from the bottom drew more extra yeast into aging, making clarification that much more challenging. A racking arm helps solve this. If you want more precise of a yeast harvest that includes more accurately the layer of healthy cells, a steeper cone will collate the different layers of yeast more distinctly. Also consider how much yeast can be collected easily and gotten rid of, compared to the less motivated ones that will only come out in rinse water and cause your BOD to skyrocket.

                      Narrower tanks cause more vigorous foaming as there are more bubbles of CO2 per sq.inch (or cm) of wort surface. More aromatics are lost in my skinny tight cone fermenter because of this. Fermcap helps, of course.

                      If you are wishing for more after fermentation yeast contact, such as in a Diacetyl rest, you will have less of the desireable yeast surface to beer contact with a steeper cone as the puddle of yeast in the bottom has a smaller circle for an upper surface.

                      Then again if you do the geometry, you find a steeper cone requires a taller tank...and a taller ceiling. The tighter cones are more expensive to produce, and narrower tanks generally cost more per barrel.


                      • #12
                        steel polish

                        Would a finer polish in the cone also effect the efficiency of yeast harvesting? I´d think that the rougher the cone is, the more yeast can settle without sliding to the bottom. As to the "racking arm" mentioned above, I assume you mean an elevated drain (a metal cylinder placed flush to the drain so that the discharge source is raised above the yeast pile - it´s the same idea as when racking from horizontal secondary fermenters.) If so, I´ve seen these in action in cylindro conical fermenters and can vouch for their effectiveness.


                        • #13
                          I have heard one very plausible explanation as to why a 60 degree cone is a very common standard. It has to do more with the manufacturer making the best use of material than anything to do with the best angle of repose for yeast, etc. If you take a flat sheet of stainless, cut out a circle, and cut that circle in half, you can make two 60 degree cones by rolling the half circles. That is the most efficient use of the stainless material. If you went with a 50 degree cone or a 70 degree cone, then you would waste most of that expensive dairy grade-polished sheet. Most tank manufacturers don't polish the entire surface of the inside of their tanks, they buy prepolished sheets and only have to polish out their welds.
                          Linus Hall
                          Yazoo Brewing
                          Nashville, TN