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Fermentation Systems For Nanobrewers

A beer fermenter is any vessel used by brewers to hold wort during fermentation. Fermenters may or may not have cooling attachments, inlet/outlet valves, insulation, covers, pressure ratings, cleaning devices, temperature probes, and wheels. And fermenters are made from a variety of materials including plastic, glass, stainless steel, wood, carbon steel, and concrete. Put all of these variables into a matrix and the number of permutations is vast. Nanobrewers, or those commercial brewing operations brewing less than 5 barrels (BBL) (155 gallons/587 liters/5.9 hl) per batch, have many options when it comes to fermenter selection because their small batches can be contained in a wide variety of easy-to-obtain vessels. This column will cover what is typically accomplished during fermentation and aging in a fermentation system, examples of fermentation systems used by commercial brewers, and strategies available to nanobreweries.

What is a Fermentation System?

A fermentation system is the total process used by brewers to house and control the process of fermentation and maturation, and sometimes includes conditioning. The first stage of this process is the actual fermentation step. During this stage, carbon dioxide, ethyl alcohol and heat are produced, the fermenting liquid usually foams, and there is an increase in yeast cell density. The removal of heat is important because fermentation temperature directly affects beer flavor by its influence on the biochemical pathways that generate esters, higher alcohols, aldehydes, organic acids, and other flavor active compounds.

As a practical note, yeast produce about 280 BTU/pound of extract fermented (per ASHRAE Handbook). This means that 3 BBLs of beer fermenting at the rapid pace of 4 °Plato/day, produces 8,812 BTUs/day. This heat load can be used by brewers to help size refrigeration equipment.

Small beer fermenters, such as 5-gallon carboys, are often air cooled and rely on the transfer of heat from the surface of the fermenting beer to the environment. This method of fermentation works best when the surface to volume ratio is large. The famous, and often photographed, open lager fermenters at the Anchor Brewing Company in San Francisco, California have no cooling jackets or coils, and are examples of larger fermenters of this type (each vessel contains approximately 100 BBLs of beer).

The problem with shallow fermenters is space, so as fermenter volume increases tanks generally become taller. Cylindrical fermenters usually have an aspect ratio (liquid height divided by vessel diameter) ranging from about 1:1 to 3:1, and sometimes as tall and skinny as 5:1. With this change in geometry comes a change in where the area is located. The open fermenters at Anchor, for example, have approximately 63% of the total surface area exposed directly to the atmosphere, compared to only 16% in a cylindrical fermenter with a 1:1 aspect ratio and 90˚ conical bottom. This means that cylindrical fermenters, even open versions exposed to a cool atmosphere, have a very large surface area in contact with the tank wall. Since tanks are made from materials that have relatively low thermal conductivities, more wall area translates to more heat retention. The take away message is that cylindrical fermenters need to be cooled.

Shallow fermenters, both open and closed, can be air cooled if the fermentation “cellar” is cool; this choice will always result in fermentations that show a rise and fall in temperature as the rate of fermentation changes. However, most fermenters are equipped with cooling jackets or coils used to actively remove the heat of fermentation from the vessel using chilled water or glycol. One advantage of coiling coils, especially in repurposed vessels, is that they can be relatively inexpensive. But coils are not easy to clean and they require considerable length to provide much area. Most tanks equipped with cooling jackets are designed to be quickly cooled (crash cooled) following fermentation. Crash cooling requires about 10 times more cooling capacity than maintaining temperature during fermentation.

Tanks equipped with cooling jackets or coils will sweat when water from the air condenses on cool tank surfaces, especially exterior heat transfer surfaces, so it is typical to insulate and clad tanks with stainless steel. This is especially common when the fermentation cellar lacks environmental conditioning. Although a nicety, insulation and cladding adds cost to tanks and is not required.

The term cellar is used to describe the space where beer tanks are located. In the days before commercial refrigeration, cellars were a literal description of underground rooms. Breweries continue to use terms like fermentation, lagering, aging, conditioning, and package release cellars to designate parts of a brewery. A brewery’s cellarman (or cellarperson) is the person who oversees the fermentation process, from active fermentation through conditioning, transfers, packaging, cleaning, and upkeep of the cellar.

The fermenting system may include some method of skimming. Many traditional fermentation systems were self-skimming, and examples include Yorkshire Squares, Burton Unions, and lager fermenters with so-called foam chambers. Open fermenters can be skimmed during fermentation, and this practice is still used by some brewers using these traditional vessels. The purpose of skimming is the removal of cold trub and very bitter hop resins, sometimes called braun hefe (brown yeast) or brandt hefe (burnt yeast), that rises to the surface of fermenting beer. Skimming systems can also be used to top-crop some ale yeast strains.

Most fermenters these days are closed, so these systems must have a vent to allow carbon dioxide to escape during fermentation. This same vent can be used to bring carbon dioxide into the vessel when the beer is transferred out at the end of the process. Closed fermenters should be rated for pressure. This is a serious safety consideration and the pressure rating of a tank should not be exceeded; period. If the fermenter pressure rating is sufficiently high, natural carbonation can easily be performed by attaching a special pressure relief valve called a spunding or bunging valve to the vent line.

While open fermenters are usually cleaned by hand, closed fermenters, especially stainless steel tanks, are equipped with spray balls to permit so-called clean-in-place, or CIP, cleaning. CIP balls are typically attached to the tank with a line running down the side of the vessel to make hose attachment easy. Cleaning solution can be added to the vessel and recirculated through the spray ball using a properly-sized process pump.

Fermentation Systems Used In Commercial Brewing

The unitank fermenter (also known as the cylindroconical tank, CCT, cylindroconical vessel, and CCV) has become the de facto standard for most breweries around the world over the last 40 years. The unitank system combines the functions of fermentation, beer maturation, carbonation (sometimes), crash cooling, and yeast collection into a single vessel. Although the modern CCT has a cone bottom, the original unitank design had a flat, sloped bottom. Dished bottom tanks can also be used for unitanks. Breweries of all sizes use this fermentation method for the production of all sorts of beers. But breweries with older equipment continue using their other systems.

Prior to the spread of the unitank, brewers used specialized tanks for each major step of the brewing process, including some brewhouse functions that have largely been replaced by the whirlpool. If we could travel back in time 150 years and walk through a typical lager brewery (I am referencing lager practices because lager breweries were principally responsible for the global spread of beer and for most of the accompanying technological developments) we would probably see a hop strainer, a coolship to pre-cool wort from the brewhouse, and a falling film chiller or “Baudelot cooler” to further chill wort going into the fermentation cellar. Many brewers of this time also used cold wort settling tanks and/or flotation tanks for trub removal, dedicated fermentation vessels for fermentation, and lagering tanks for clarification and conditioning. With the advent of pressure rated, glass-lined steel tanks, and later stainless steel tanks, brewers could completely finish the aging and conditioning (also known as carbonation) portion of the process in a single lagering tank.

The ale tradition was similar in many aspects where fermentation was conducted in fermentation vessels and conditioning occurred in the cask. Cask conditioning is not too different from lagering in that clarification, carbonation, and flavor maturation all occur in the same vessel. The main difference between cask ales and traditional lagers is that lagers were racked out of the lagering tank into the barrel after aging was complete.

Nanobrewing Strategies

Nanobreweries have the size advantage of really being able to choose from a wide variety of fermentation strategies to accomplish the goals of fermentation while also keeping with the DIY tradition of homebrewing. Like larger craft breweries, many nanobrewers use CCTs because these vessels are very handy and readily available on the small equipment market.

But if you want to build a cellar that is more akin to old school brewery design, options abound. Simple fermenters can be fashioned from food-grade plastic containers, stainless steel drums, and stainless steel portable tanks (IBC or intermediate bulk containers). All of these vessels have flat bottoms, so yeast harvesting can be a challenge if there is not a low-point outlet. But harvesting and re-using yeast is a general challenge with low-volume production and many nanobrewers prefer using liquid and/or dried yeast strains that are not re-used. These vessels can be used with or without cooling jackets or coil depending on the cellar design. Open vessels are easily equipped with removable coil systems that resemble immersion wort coolers, and also can easily be covered with a simple lid to keep dust and debris out of the vessel. If you build your own cooling coils, make sure to use stainless steel tubing instead of copper, as copper can impart a metallic flavor to beer and can also lead to oxidation if exposed for too long (copper is fine for wort cooling though).

Whether using a CCT or repurposed vessel with cooling coil, the nanobrewer can locate these fermenters in any clean, tidy environment without having to worry much about the environmental temperature. If the fermenters are not equipped with cooling provisions, the smaller fermenters can be placed in a controlled environment, such as a walk-in cooler. And these small vessels can easily be moved using wheel kits, pallets and pallet jacks, and hand trucks.

Brewers not using CCTs or some other type of unitank usually rack their beer into another vessel for a variety of purposes including maturation, carbonation, or priming for transfer to bottle or keg. If flavor maturation occurs in the fermenter, a single secondary vessel may be sufficient for packaging preparation. For brewers who filter their beers, this vessel is often referred to as a bright beer tank (BBT) and can typically be turned around in a couple of days. Depending on the batch size, kegs can be used for maturation vessels, and can be stored on a wooden rack that keeps the kegs tilted so that clear beer can easily be racked out of the aging keg into another keg or bottle for serving.

The nice thing about all of these methods is that transfers are not much different from homebrewing. Small pumps, gas pressure, gravity and racking canes can all be used to transfer beer from one tank to another, and short hoses with relatively low cost connection types, like beer nuts, can be used for transfer operations. Things change as the batch size approaches 10 barrels (11.7 hectoliters) where sanitary process pumps and beer hoses with tri-clamp or the threaded DIN (Deutsche Industrial Norm) connections are more commonly used. Although similar to operate, these tools are more expensive.

My Dream Cellar Configuration

I spent 20 years working for a stainless steel fabrication company and worked on a wide range of brewing tank projects for brewers small and large. It became apparent to me early on that CCTs are under-utilized for every step of the brewing process. The real benefits of these relatively expensive vessels is the reduced cost associated with filling, emptying, and cleaning, and lower risk of contamination and oxidation that comes with multiple tank transfers. These benefits are significant to commercial brewers and explain the popularity of CCTs. However, artisan brewers can certainly mitigate the microbiological and oxidation risks that come with multiple transfers by using good brewing practices and paying attention to details.
So why are CCTs under-utilized during use? For starters, they require a relatively large headspace when used for fermenters because of their skinnier aspect ratios (foam sticks to surfaces, so tall tanks require more extra volume in comparison to shallow fermenters). But when the CCT is being used as a fermenter it has a pressure rating that is usually not required, more cooling surface area than needed, and insulation and outer cladding that is unnecessary.

Now look at the CCT after the beer has been chilled. It has excess volume that is no longer occupied with beer foam, and has way more cooling surface than required to simply keep the beer cold. CCTs have cones that are pretty handy for both fermentation and maturation, but the cones are not absolutely required.

My dream cellar is one where fermenters are designed to maintain temperature (remember small tanks do not require cooling jackets if the air temperature is sufficiently cool), keep the beer from over-foaming, and equipped with a cone to make yeast harvesting easier. After fermentation, beer is transferred to mobile, pressure-rated tanks where flavor maturation, carbonation, and gravity clarification occurs. The tanks are mobile because I want to mature and carbonate at fermentation temperatures, and clarify/chill stabilize at cold temperatures. This is where the portable part is important.

This means that my dream cellar is an appropriately sized walk-in cooler with a portion or portions controlled to fermentation temperature(s) and another portion that is held at about 32 °F (0 °C). The whole unit is cooled in the cold section and the fermentation cellar(s) is cooled by a fan that thermostatically blows cold air into the cellar with the return air flowing through a controlled louver that closes when the fan does not run. All tanks are optimized for their specific duty, and the total tank cost is reduced. Since there are lots of used walk-in coolers that can be purchased for a pretty low price, the additional cost of the cellar is offset by the reduction in tanks cost. This idea is just an example of how nanobrewing fermentation solutions can be customized to satisfy brewing philosophy, brewing dreams, and brewing budgets. Think big and brew small!

Closing Thoughts

Fermentation cellars are the most expensive part of most brewing operations and have a profound influence on how wort is transformed into beer. The practical brewer needs to consider the things that will or may occur in the cellar in order to design a cellar that is efficient, practical, flexible, and cost-effective. All good designs begin by listing the functional requirements of the system and choosing equipment that satisfies these demands, rather than modifying the brewing process around avoidable equipment limitations.