After buying the new George Fix book, "An Analysis of Brewing Techniques" and reading the section on unitank design, I did a little brainstorming about the implications for small brewers. Namely what kind of costs and problems would come up when trying to design a squat cylindroconnical fermenter instead of a traditional tall fermenter.

What I did was modelled two fermenters of the same volume but one of the tall geometry and the other using the squat geometry discussed in the book

For example:

24 gallons total volume

¹ both cones use a 60 degree internal angle
² Squat fermenter designed using space conservation. Unterstein, K. 1994. Brauwelt 12:4

In many cylindroconnical fermenters, temperature control is achieved by pumping chilled glycol around a jacket covering the fermenter. Regulation of the temperature occurs either by turning the pump to the glycol on and off or by a valve which regulates its flow.

In homebrewery system unitanks where the volume is less than 1 barrel, the glycol jacket does not completely cover the vessel. Instead, these fermenters have a small chill band placed around the fermenters' cylinder. For example:

The reason that a chill band is probably used is to reduce the cost of fabrication. It is assumed that since most to the wort is in the cylinder portion of the fermenter, it will mix with the wort at the extremity of the unchilled cone.

In the squat fermenter design however, there is 2.5 times as much wort in the cone as in the tall fermenter. If you take in account that these fermenters are not design to be filled to the top, you have an even greater percentage of beer in the cone. For example, assuming you fill the fermenter allowing for 20% head space, you now have 1/3 of the wort in the cone in the squat design. It may therefore be necessary to chill the cone as well as the cylinder above in order to avoid large temperature gradients.

The consequences of building a jacket around the entire fermenter may be several:

1) Increased cost of chilling. A larger volume of glycol will be required in the squat fermenter design. Many small fermenters are not insulated with a barrier between the glycol jacket and the outside atmosphere. Since a larger jacket leads to greater surface area to contact the outside air, you can expect larger loses of glycol temperature due to lac of insulation. This may even necessitate insulating the fermenter at additional cost.

2) Increased cost of fabricating the fermenter. This is an obvious problem. There will be very definite cost associated with building a second cone around the bottom to house the glycol and additional costs in getting the glycol to circulate around the jacket uniformly.

3) More problems with cold spots due the the relative glycol chilling to volume of wort at the bottom of the cone. At the tip of the cone, the amount of wort becomes very small. If the volume of glycol in the outside jacket is determined by a constant distance from the inside shell there may be a problem with too much cooling at the base. This may also be acerbated by the fact that the cool wort will want to settle in the cone due to thermodynamic currents.

Anyways, food for thought. If I made any of my comments unclear, feel free to email me and I'll try to make it more clear.

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