Fundamentals of Stainless Steel Conicals

Throughout history brewers have probably utilized every type of vessel they could get their hands on to ferment their brew. From sheepskins, clay pots, glass, enamel, and everything between. The English had their open wood vats and Burton union fermenters. The Belgians utilized open flat coolships for natural cooling and also spontaneous fermentation. Lager breweries in Europe used pitch-lined open fermenters. And like brewers today, they adopted new technology to brewing whenever they could.

In the “dark ages” of homebrewing in the ‘70s, about all that was available were glass carboys and plastic buckets. That was still the case when I started homebrewing in the early ‘90s. At that time, all-grain brewing was less common than it is today, but as soon as I got a handful of extract batches under my belt I made the move to all-grain. I quickly discovered that it was super fun, but it took a lot more time. So I began to think about bigger batches to make my toil worth the effort. I was tired of using multiple carboys, and racking them into yet more (secondary fermentation was a big thing back then). I finally managed to find a 12-gallon (46-L) Nalgene jug with a bottom valve. I used it for a few 10-gallon (38-L) batches, but I had one batch get contaminated and the thing was really hard to clean. So the search for a larger vessel went on. I did take a house remodel sabbatical in the mid-‘90s, and three little girls added into the mix so it wasn’t until the late-‘90s that I began again looking in earnest to get that larger fermenter.

Introducing Conicals to the Homebrew Market

In my search, I stumbled across a supplier I had never used before called MoreBeer!, which had a small stainless conical on their webpage. But there was no way I’d get that expense by my wife. So as my engineer mind drew into deep thought, I had this hair-brained idea to make five of them and sell three on this new thing called eBay to pay for the other two for myself. Certainly this would pass muster with the wife. After much negotiation I made the plunge.

Anita Johnson, the owner of my local homebrew shop in Indianapolis at the time, soon convinced me I should sell these through retailers. That was the launch of Blichmann Engineering. I can’t thank Anita enough for giving me that nudge. I also can’t tell you how many retailers that I called who told me I was an idiot to think that anyone would pay that much for a fermenter. But I did manage to convince a handful of retailers and set up shop in my garage selling a whopping 3–4 a month. In a couple years I found I had two full-time jobs and left my engineering job at Caterpillar and went full time Supreme Commander of Blichmann Engineering. Well, I was also Mr. Mom to three daughters, too. It was pretty cool, looking back, to be a pioneer along with MoreBeer! in the high-end homebrew-specific stainless steel products. To see things evolve from a niche little hobby market to a mainstream hobby where buying stainless conicals is now commonplace is pretty awesome. How the times have changed!

Defining Conical

What is a conical and what does uni-vessel mean? The term “conical” or “cylindro-conical” are merely reflective of the shape of the device. The conical portion aids in collection and discharge of sedimentation to the bottom of the cone where a discharge or “bottom dump” valve is affixed. The cone angle is commonly 60 degrees, but you’ll see shallower cone angles as well. Generally, the steeper the cone the better the removal of sediments. But also the taller the unit needs to be for a given volume. That is not really an issue for homebrewers, so the 60-degree cone angle is pretty standard. The cylindrical section holds the bulk of the volume.

The term uni-vessel or uni-tank means it is capable of holding pressure adequate for carbonation. Nearly all commercial, and most homebrewing conicals these days, are able to hold pressure up to 15 PSI and have cooling capability, so this allows them to be utilized for both fermentation and carbonation. Although, in practice, carbonation in a conical is rarely done in commercial brewing. Usually the brewers allow time in the conical for the beer to clear reasonably, and then it is transferred to a bright beer tank for final clarification and carbonation. From the bright tank, the beer is either transferred into bottles, cans, or kegs. For homebrew-size batches, it makes financial sense to transfer the finished beer straight into kegs (or bottles) since kegs can be had for a fraction of the cost of a stainless conical. And you can get another batch in the fermenter much sooner since it isn’t tied up dispensing. That said, this is a hobby and some brewers love the gadgets and showpieces in their brewery. I fully appreciate that!

The two defining features for conicals are the bottom dump and the rotating racking arm. Let’s start at the bottom (of the conical).

Bottom Dump

Having a drain on the bottom of the vessel eliminates the need to rack (transfer) to another vessel for secondary fermentation. Secondary fermentation (racking to a second fermenter to separate the wort from the trub after fermentation is complete) used to be recommended for all beers, but these days using a secondary fermenter for ales is pretty uncommon. That said, it is so fast and easy to dump sediment in a conical that there really isn’t a reason not to “secondary.” Lagers definitely benefit from racking off excessive sediments for long-term maturation. What’s great about the conical, is you simply open the valve and dump the sediment, leaving the clear beer behind. This is also where you can collect yeast for repitching (more on that later). Not only is this a significant time- and cost-saver, it reduces the potential for contamination and oxidation. I always recommend dumping sedi- ment from the bottom dump valve after high kräusen, and then again in a week or so for lagers. For ales, normally only one sediment dump is needed.

If you’ve waited too long to dump the sediment you might open the valve and discover that it doesn’t drain. Wait patiently for it to begin flowing, and be ready to close the valve quickly. When compacted, yeast is a non-Newtonian fluid. Meaning it is more like toothpaste than molasses. So it can support the weight of the beer above it even with the large butterfly valves commonly used on conicals. If you have a stuck dump, applying a little CO2 pressure to your tank will usually get things moving again. But, of course, never exceed the pressure rating of your fermenter.

Beyond dumping the sediment, the primary use for the bottom dump is for harvesting yeast. The key benefits are generating large healthy yeast pitches for future batches, and saving money on yeast. This is a particularly great option if you brew frequently and use the same yeast strains regularly. If you’re a brewer that likes to tinker with all sorts of strains this may be a less attractive feature. Similarly, if you’re an infrequent brewer you may not be able to keep the yeast healthy between batches. If you’re unable to pitch the yeast for another couple of weeks you’ll want to reactivate the yeast with wort before using. And after four weeks you’re safer going with a new package of yeast.

The process of harvesting yeast is fairly simple, but it does require strict adherence to sanitation. After the main fermentation activity has slowed (high kräusen has passed), you’ll want to drain trub, hop particles, and early flocculating yeast from the bottom of the cone using the dump valve. It is handy to have a sanitized large diameter hose connected

to the valve. Be sure to spray sanitizer in the valve as well. If you have a conical that can hold pressure, add a couple PSI of CO2. Much more than this and you’ll spray the yeast aggressively out of the valve. Slowly open the valve and let the brown trub and green hop material pass. Close the valve and spray sanitizer on the inside of the valve. If you have a cap to cover the open end of the valve that is advisable to keep the inside surfaces sanitary. If you haven’t put pressure on the tank, simply use a sanitized CO2 hose through the airlock hole to purge any oxygen out of the headspace. Run CO2 for a few minutes. It isn’t necessary, or advised, to immerse the hose in the beer. A few days later, repeat the process, again being sure all surfaces and the hose are well sanitized, as you’ll be collecting this yeast for reuse. Alternatively, you can collect the yeast in one step by letting the brown trub pass into a waste container and collecting only the cream colored yeast.

Two excellent storage containers for yeast storage are Mason jars or Erlenmeyer flasks. However, it is important to keep yeast harvested in clear glass out of direct sunlight as much as possible. If using a Mason jar, you’ll leave the lid on slightly loose to let CO2 escape. For the flask, you’ll use an airlock and stopper, cotton plugs, or a piece of aluminum foil secured with a rubber band. Purging the container with CO2 before and after filling is recommended. Yeast can be stored in a refrigerator for a couple of weeks and 4–6 generations is common in a home setting.

Racking Arm

The second defining feature of a conical is the rotating racking arm. While some manufacturers offer this as an optional item, it shouldn’t be. This is the easiest way to transfer the clear beer to your kegs or bottles while leaving the sediment behind. This curved rotating drain tube and valve allows you to begin draining into your keg (or bottling bucket) and then you slowly rotate the arm downward until you see a bit of yeast being drawn through the hose letting you know you’ve reached the yeast cake. Then rotate it back slightly and continue to drain. The racking arm is also a great place to take gravity samples to monitor fermentation progress. Spray some sanitizer inside the valve, and then simply open the valve and fill the sample cylinder. Then spray the surfaces again to sanitize and remove beer drips from the valve after taking the sample to keep bacteria and mold off of the surfaces for subsequent samples and draining.

One thing to keep in mind is that when you’re removing beer from a fermenter, is that you’re also drawing air into the headspace to replace the beer you’ve just removed. The easiest way to ensure you don’t leave oxygen in the headspace for a long time is to apply a bit of CO2 pressure to the tank prior to drawing a sample or dumping sediment. The CO2 will simply expand to keep any oxygen out. A couple PSI is plenty. If you don’t have a pressure-capable tank, the best option is to purge the headspace after a dump/ sample by placing a CO2 hose in the airlock hole as described earlier.

Transferring From a Conical

Two ways to transfer beer from the conical to a keg without introducing any oxygen are (left) using a gravity transfer where a return hose from the keg is connected to the conical so the CO2 being pushed out of the keg returns to the head space of the conical. Another way (right) uses CO2 to push beer through a hose from the racking arm of the conical into the liquid-out post of the keg (open the vent of the keg to release any CO2).

The simplest way to drain your beer from the conical into a keg or bottling bucket is gravity. It is super easy to connect a hose to the racking arm and place the other end into the bottom of a CO2-purged keg. But this requires the fermenter to be elevated above the receiving vessel.

Fortunately, most conicals on the market have enough pressure capability to allow you to pump your beer using CO2 pressure — something you’d never do with glass. This feature makes lifting the fermenter above your keg, or using leg extensions, unnecessary. Connect the racking arm of your conical to the liquid-out post of the keg. This fills the keg from the bottom up. Open the pressure release valve (PRV) of the keg to vent any CO2 pressure and leave it open. Add a couple PSI of CO2 pressure to the conical and then open the racking valve. You should see beer begin to flow. If it doesn’t, increase the pressure slowly until you do. The idea is to slowly make the transfer to avoid foaming. Watch the transfer closely so you can quickly shut off the racking valve when gas enters the hose, signaling that the fermenter is empty. Gas pumped through the beer might result in a bit of a mess. If beer comes out of the keg relief valve stop the transfer. If your keg is not full to the brim, pressurize the keg and pull the PRV a few times to expel any air that may have entered the keg.

If the beer has been carbonated in the fermenter, you will need to “counter-pressure fill” your keg. To do that you’ll need an adjustable relief valve affixed to the CO2 post, connected to your gas post. This allows the keg to be pressurized, to the same pressure as the fermenter, and then slowly releases the CO2 gas in the keg until the beer flows. This keeps the CO2 in solution and prevents excessive foaming. Adjust the pressure of the keg to a slightly lower pressure than the fermenter. Set the adjustable relief valve a little higher than the conical pressure. This is done to prevent CO2 gas from blowing back into your fermenter from the keg and kicking the yeast back into suspension. Open the racking valve and the beer should begin to flow. When you hear the CO2 regulator stop flowing, gradually open the relief valve until you hear CO2 hissing out of the valve. Leave the adjustable valve at that setting until the keg is full. When the hose fills with CO2, or beer sprays out of the PRV, stop the transfer by closing the racking valve.

Temperature Control

Ice water or glycol can be recirculated through an immersion cooling coil as a way to control temperature inside of a conical. Insulation jackets will help maintain the temperature.

Temperature control of any fermentation is paramount. The old school and simplest method for homebrewers to cool their conicals is by utilizing a refrigerator or upright freezer and overriding the thermostat (there are a number of controllers on the market for this). Simply tape the temperature probe onto the side of the conical with a piece of thermally conductive aluminum duct tape and you’re good to go. This reduces cycling of the refrigerator, reads very accurately, is very quiet, extremely reliable, and there is nothing extra to clean.

Another common option is to use an immersion type cooling coil and insulation jackets that most conical manufacturers offer for their products. This requires a supply of cool liquid to be circulated through the inside of the cooling coil. On the simple side this can be a cooler of ice water and an immersion pump. The real drawback with this method is that the frequent addition of ice to the cooler can be a chore. A more elegant, but more expensive, way is to use a glycol chiller. These systems utilize a refrigeration system to cool propylene glycol (a food-grade antifreeze) that is pumped through the cooling coil inside of the conical. All these methods do an excellent job of maintaining your fermentation temperature and can take your fermentations to the next level of control.

Fermenting Under Pressure

If you’ve got a fermenter that can handle up to 15 PSI you’ve got the opportunity to do pressure fermentations to suppress ester formation and ferment at room temperature, and avoid the need for dropping your fermentations to lagering temperatures. Plus you can finish the batch at the speed of an ale! Chris White from White Labs and I did an experiment a few years ago on the flavor of lager fermented in the traditional way, and also at room temperature at 0, 1, and 2 BAR (0, 15, and 30 PSI). Chris quantitatively analyzed the finished beer (Munich helles) utilizing a gas chromatograph (see the results in Table 1, below). The pressure resulted in a very significant reduction in esters (ethyl acetate and isoamyl acetate). From the independent qualitative tasting done by high-ranking Beer Judge Certification Program judges, the winner was still the traditional lager method, but the 1 BAR (15 PSI) room temperature batch was a close second. The 0 BAR (0 PSI) was notably more fruity. The 2 BAR (30 PSI) batch had hop bitterness that was a little harsh and had a little thinner mouthfeel. Another focal point to notice is diacetyl. The room temperature fermentations were all very low in diacetyl. While the beer fermented in the traditional method had a more typical level of diace- tyl for the style. This is likely what tipped the win to the traditional la- ger as it had a fuller mouthfeel and rounder balance.

If you’re interested in experi- menting with pressure fermentation then a spunding valve is needed. Note that a PRV is only intended to be activated in an accidental over-pressure situation. Using a PRV as a spunding valve is akin to installing a fire alarm in your house because you have faulty wiring. It is always better to fix the wiring. Or in this case, use a spunding valve according to the manufacturer’s instructions.

Conical Care

When you get a new conical there is a step that should be taken before initial use — passivating. Initial cleaning and passivating of a new stainless fermenter is pretty simple. The purpose is to thoroughly remove any manufacturing residue including oil and polishing compounds. PBW, AmBrew, or plain detergent all work well for removing oils and polishing compound residue. Follow that up with an acid cleaner like Bar Keepers Friend (oxalic acid), which is available at any grocery store. Simply sprinkle some on a sponge and scrub away. Bar Keepers Friend is slightly abrasive, so highly polished surfaces may exhibit some swirl marks, but this is not harmful to the stainless, and won’t affect performance. Another acid commonly available at homebrew stores is citric acid, which also works well for passivating. Stainless steel is considered “passive” when the surface has developed a thin (several molecules thick) layer of chromium dioxide. So the idea behind “passivating chemicals” is to clear the surface of things like wax, oil, water salts, and soils so that the oxygen in the air can react with (oxidize) the chromium on the surface of the steel. That’s why it is also important for you to let the surfaces dry completely after cleaning. It is the oxygen reacting with the chromium that does the passivating, not the chemicals. The chemicals are like eHarmony — they just aid in arranging the meeting! It is this thin layer of CrO2 that is extremely stable and resistant to corrosion. After the initial cleaning, you’ll be able to use any alkaline cleaner to keep the surfaces squeaky clean, but an occasional scrubbing with Bar Keepers Friend is recommended to keep the passive layer in good shape.

After that initial cleaning, future cleaning, sanitizing, and care for your conical is fairly simple. The latest craze is CIP (clean in place). This is accomplished with pumping cleaning and sanitizing agents through a spray ball mounted inside of the tank to mechanically and chemically clean the tank. This is the process used in commercial breweries by necessity — it is virtually impossible and certainly impractical to clean the larger vessels any other way. Even after cleaning your tank in this manner it is important to inspect all ports and hatches to ensure that the spray ball was able to reach these areas.

For homebrew-sized vessels, it is certainly possible to manually clean them, and it is generally faster and more thorough to just scrub and sanitize by hand. Particularly when you add in the setup time for CIP pumps and hoses. Ultimately, it is a matter of choice. If using CIP, be sure to choose cleaning and sanitizing agents that are non-foaming. For manual cleaning, a product like PBW or AmBrew is great for soil removal and StarSan or SanStep for a spray surface sanitizer. In the old days it was common to fill a fermenter completely full of sanitizing solution. But with the modern acid sanitizers simply spraying the surfaces is more than adequate and saves a lot of time and money.

One of the things that make conical fermenters useful is the plethora of accessories that can be added. Rotating racking arms, carbonation stones, thermometers, blow off tubes, cooling coils, insulation jackets, and much more. It also makes them look pretty cool. But all of that comes with a hidden cost (in addition to the actual cost) — lots of extra cleaning. So when selecting accessories, realize that you’ve got to disassemble and clean and sanitize all those items! I’ve always been a fan of simple is better, so factor that into your decisions too. Remember that commercial tanks have many of those accessories because there is simply no other way to accomplish some tasks in any other way.

 Safety Considerations

A pressure relief valve is a critical piece of safety equipment to ensure the conical is not over-pressured.

Conical fermenters do resolve a lot of the safety issues of fermenting in glass. But they also introduce a couple other issues that warrant discussion. They tend to be top heavy due to the nature of their shape. Not really a big issue unless you add casters to them and want to move them or lift them. They are also available in sizes larger than 5 gallons (19 L), so they can get quite heavy. Be sure to follow the manufacturer’s warnings for handle capacity if you intend to lift when it is full. When moving with casters, take extra care to avoid tipping.

For pressurizeable fermenters let’s have a discussion about pressure (P), area (A), and force (F). Pressure is the force exerted over a given area. While 15 PSI doesn’t sound like much, that is all relative to area. Specifically F = P x A. Where area (for a circular lid) = Diameter2 x 3.14 / 4. For a conical with a lid that is only 6 inches (15 cm) in diameter, the force on that lid at 15 PSI is 15 x 62 x 3.14 / 4 = 424 lbs. (192 kg) of force. For a 16 inch (41 cm) diameter lid, that force jumps to 3,000 lbs. (1,360 kg).

I go through this exercise so that you recognize how important it is to have a PRV on your fermenter at all times. And how important it is not to tamper with it. ALWAYS release all pressure before attempting to open any hatch on the fermenter. Even a plastic lid with that kind of force on it can cause serious injury. Not to mention a colossal loss of beer! While it is tempting to assume that you’ll be fine without a PRV if you’re using a blow-off tube or airlock, if any of those devices clog your yeast will easily tolerate over 30 PSI and can cause a severe over-pressurization. Don’t be penny-wise and pound-foolish.

Time to Get a Conical?

A frequent question when buying a conical fermenter is selecting the right unit for doing multiple size batches. While you can make a 5-gallon (19-L) batch in a 10-gallon (38-L) conical, it is even more important to pay attention to keeping oxygen out of the tank after fermentation activity has stopped. The other drawback is that you will have less static pressure to discharge yeast from the reduced level of beer in the fermenter. That is easily remedied by adding a little CO2 pressure if needed. In general, I’ve always recommended going with the batch size you do most often, and sacrifice on the other batch size. If 90% of your batches are 5 gallons (19 L), and 10% are 10 gallons (28 L), go with a matching size for the 5-gallon (19-L) batch, and fill a carboy with the extra 5 gallons (19 L) you’ve made on those less frequent occasions. If you’re torn, go with the bigger size. In general, a 10-gallon (38-L) batch size conical isn’t a lot more cost than a 5-gallon (19-L) batch size unit.

Material of construction is also a core decision to make. One of the key things I love about stainless steel conicals is the rugged durability. Glass carboys are awesome for corrosion resistance and overall ease to clean, but are quite fragile and present some serious safety issues. We’ve all seen the cuts and carnage from glass. PET conicals eliminate the safety issues of glass, but care must be taken to use the right chemicals for cleaning, and at cooler temperatures to prevent damaging the material over time. Being a softer material, you’ll want to avoid cleaning with anything abrasive that may damage the interior surfaces. Stainless is also UV impermeable so no light-struck beer issues! Like glass, stainless steel is also impermeable to oxygen. PET plastic has a fairly high resistance to oxygen ingress, but is not impermeable. Of course, plastic conicals will be more cost effective.

It has been truly amazing watching the development of home-scale conical fermenters over the past 20 years to where they are now fairly commonplace. I hope this article has taken some of the mystery out of all the valves and fittings on these devices. As you’re selecting a conical fermenter, recognize that it is really a balancing game of features and benefits you’ll actually use, against the price. And let’s be honest, another driver is that cool look to dress up your brewery. After all, this is a hobby! 

Issue: September 2020