My ale brewing evolved from three gallon extract batches in the kitchen to 11 gallon all grain batches in the garage. The process has been kept simple so I can enjoy it. Wort and beer movements are minimized and are mostly powered by gravity or CO2. Cold side temperature control does have room for improvement as some styles can only be brewed well in cool weather.

Last year, I did the taste workshop for some Fear No Beer members who were preparing for the BJCP exam. We met in Mark Cherney’s Mission Viejo garage which houses more beer stuff than mine does. I spotted a small blue cube connected by two hoses to a water filled tub. Mark explained that the blue cube was an aquarium chiller used for fermentation temperature control (FTC). Wow! That’s pretty clever and the light over my head switched on.

A Variety of Ways to Chill Wort

We have dogs and I’d never heard of aquarium chillers. They are small refrigerators that cool water to keep fish or yeast happy. Some can multitask by also controlling a heater if the water gets too cold. Mark’s is a 1500 BTU/hour unit he found on EBay for $200, which was about half retail.

I spooled up on FTC by studying the usual suspects; water baths with and without aquarium chillers, foam boxes like Ken Swartz’s Son of Fermentation Chiller, refrigerators, Peltier devices and the latest homebrew toy - a glycol cooler powered by the guts of a window air conditioner.

Why Chill Wort At All?

My effort screeched to a halt when I recalled that most of the tasty fermentation products (esters, phenols and higher alcohols) are created the first day or two after pitching. To manage these compounds, I needed to be able to pitch at lower temperatures. Then, FTC could be meaningful.

There are some primitive wort cooling methods; do nothing, water or ice baths, snow banks (probably not at the beach), dilution water and sanitized ice but none can quickly cool a large volume of boiling wort. If you brew extract or small all grain batches, one of these methods might work for you.

Immersion vs. Counterflow Chillers

Dave Cordrey wrote an excellent article that reviewed wort cooling basics. It’s in the Technical Information section of the club website. He discussed immersion coolers (IC) with water flowing inside copper tubing and counter flow coolers (CFC) where wort and water exchange heat inside the device. My story builds on Dave’s.

Before this project, my wort was cooled with tap water once through a small IC. After it reached 80-90°F, chilled water from a cold plate finished the job. This setup, a holdover from my five gallon batch days, couldn’t achieve low enough temperatures for 11 gal batches year round and cooled too slowly.

I learned more about cooling systems and found that each one has its own downside. Here are the big ones in my eyes:

• Undersized ICs cool slowly allowing the production of DMS above 140°F and wild yeast and bacteria a chance to thrive between 140 and 80°F.
• Recirculated wort is vulnerable to staling reactions due to Hot Side Aeration (HSA). There is an ongoing debate about HSA and research continues to better understand its mechanisms.
• CFCs can be difficult to sanitize, allowing the most unwelcome flavors to get started.
• CFCs allow volatile hop flavor and aroma to evaporate by keeping the bulk of the wort hot longer than ICs.
• CFCs complicate hitting a specific pitching temperature.

Commercial brewers do find that CFCs meet their production needs. One benefit is that they can be used in a contained system which lowers infection risk as long as good sanitation is practiced. Even then, there’s a downside. If you ever wondered why the Randall and Torpedo had to be invented, loss of hop flavor and aroma is your answer.

For almost 90 years, commercial brewers have specified plate CFCs more often than not. These are amazingly efficient but there’s no free lunch, as discussed on a Wiki. “In HVAC and brewing applications, heat exchangers of this type are called plate and frame; when used in open loops, or with fluids that transport solids, these heat exchangers are normally gasketed to allow periodic disassembly, cleaning and inspection. There are many types of permanently bonded plate heat exchangers, such as dip-brazed and vacuum-brazed varieties, that are often specified for closed loop applications.”

Hose and tubing CFCs have been available to home brewers for at least 30 years. Therminator and Shirron plate coolers have been marketed for the last five along with others that can be found online. None of these coolers can be disassembled for cleaning and sanitizing. CFCs have some attractive features, but I’ve heard and read about too many infected batches when sealed ones are used. I think no CFC can be reliably sanitized unless it can be completely taken apart and visually inspected.

Here’s a photo of a freshly opened plate cooler. The light brown stuff isn’t exactly good for your beer.

CFCs aren’t for me until I can find an affordable version of something like this.

Even though cleaning and sanitizing an IC is easy, some home brewers still worry about their limitations. Recently, Jamil Zainasheff published his version of a wort recirculation/IC scheme that rivals CFCs for speed and low temperatures (ed. we have Mylo's build of Jamil's chiller right here). This is intriguing, but the possibility of HSA from energetic mixing bothers me. Perhaps a look at the science of heat transfer can lead us to quick cooling with a minimum of complications.

The Science of Heat Transfer

Boiling wort’s excess heat can be calculated with

H = M*Cp*ΔT

H equals the product of M, the wort’s mass, Cp, its specific heat and ΔT, its temperature change. My worst case is 11 gallons of 1.080 wort that weighs 100#, has a Cp of 1.05 and a ΔT of 150°F. Allowing for the heat retained by the kettle and IC, the total is 17,000 BTU in round numbers. Removing this heat in less than an hour will allow the yeasty beasties to start dining and repel unwanted guests.

The rate of heat transfer can be calculated with Q=U·A·ΔT. Q equals the product of U, the overall heat transfer coefficient, A, the area of the coil and ΔT, in this case, the average difference between the wort and coolant temperatures during the entire process. Engineers deal with this ΔT using the Log Mean Temperature Difference concept but we don’t have to go there. For our purpose, clues to quick cooling can be teased out of the terms on the right hand side of the equation.

• U - High coolant flow, a clean coil inside and out and moving wort all increase the rate of heat transfer.
• A - Greater immersed area also increases the rate.
• T hot - Start and end wort temperatures are 212 and 62°F.
• T cold - Chilled water speeds things up by increasing ΔT.

My local tap water varies between 57 and 72°F from winter to summer. Because a ΔT is required to push heat from the wort to the coolant, some chilled water is necessary to even reach 62°F wort year round.

Changes that can speed wort cooling the most without bad compromises are:

• Increase U by keeping the coolant flow rate high and constantly but gently stirring the wort.
• Increase A by replacing the old 30’ long 3/8” tubing IC with a 50’ long ½” one. This is a 200% area gain.
• Increase ΔT by replacing the cold plate with a chilled water recirculation pump. This also increases the flow rate which increases U.
• Reality check. A U of 30 BTU/hr-ft2-°F is required to remove 17,000 BTU/hr with the large coil. IC U’s can range up to about 250, so my plan is realistic.

Hardware notes:

• ICs can be purchased. They can also be built for slightly less money out of pocket. Prices vary a lot, so shop around. If you build, Lowe’s has copper tubing almost as cheap as sources like coppertubing.com but their sweat soldered fittings are expensive. Even Ace Hardware’s fittings are 50% cheaper than Lowes.
• Soft ½” refrigeration tubing can easily be formed by one person into a 9” OD coil but fittings are easier to install than trying to make sharp bends.
• Refrigeration tubing is specified by OD and fittings by ID. ½” tubing and ⅜” fittings mate perfectly. Go figure.
• Only use lead free solder.
• Roll your own video.

To the right is a photo of my new coil. Some are prettier and some are uglier but coils with the same immersed area all work about the same.

Motorized Stirrer

I have better things to do than stir wort. Machines to do this can be found on forums like Home Brew Talk. I found a low speed gear motor, a Molon EM5R-63-1, for $25 online and assembled a stirrer from workshop scraps. The grey can in the middle of the photos is the motor and below it is the gearbox. The black box on the left holds the motor’s start/run capacitor.

One quart yeast starters and complete wort aeration allow my fermentations to show activity in 2-3 hours. I’ve rarely (knock on wood) suffered unwanted infections. Because of those experiences I mounted the stirrer on a piece of stainless that leaves the kettle top open. This allows DMS a chance to evaporate and the wort to cool a bit faster.

Other stirrer drivers that might work are:

• top mounted ice cream machine motor (I tried a bottom mounted one but the dang thing was just too complicated to convert)
• cordless drill (OK but awkward to mount)
• hand mixer (find one that can be slowed to 60-120rpm)
• rotisserie motor (might be too slow)

Impeller:

• Radial and axial flow impellers each work well and can be fabricated from sheet metal.
• To start, I chose a simple radial flow paddle.
• Brass, copper or stainless steel are the preferred materials for any parts that touch wort.
• Carbon steel is a poor choice as it can add iron’s off flavors to the beer.

Stirrer Operation:

• A 4”x2” paddle spinning about 60 rpm rotates the entire wort mass at 5 rpm in my kettle. Recirculation rotates wort at about 10 rpm, so I’m where I wanted to be.
• The stirrer is also run after cooling to create a trub cone at the bottom center of the kettle.

Chilled water recirculation pump:

Jim Hilbing uses a Little Giant 5-MSPR-WG submersible pump to recirculate chilled water through the second of two CFCs in his brewery. This reliable pump has a maximum discharge of 20 gpm, a shut off head of 26 feet and retails for about $100. I shopped around to look at the competition. All the big box and hardware stores carry submersible (they are also called utility, pond or sump) pumps with similar specs. Harbor Freight was the cheapest at $40 for their Pacific Hydrostar model 98342. Most of Harbor Freight’s stuff is crap in my eyes but I’ll roll the dice on a pump that may only run 12 hours a year. Here’s a photo of the 98342.

Results of a series of step by step tests:

Baseline

• 72°F tap water through the small coil
• Followed by water chilled with the cold plate in an ice bath
• Intermittent stirring with a spoon
• One hour to cool 11 gallons to 72°F in July

Test #1

• 62°F tap water through the large coil
• Followed by water chilled with the cold plate in an ice bath
• Intermittent motorized stirring with a radial impeller
• 55 minutes to cool 7.5 gallons to 62°F in Dec
• 140°F was reached in 3 minutes and 80° in 15

Test #2

• 59°F tap water through the large coil
• Followed by water chilled with the cold plate in an ice bath
• Continuous motorized stirring
• 45 minutes to cool 11 gallons to 62°F in Jan
• 140°F was reached in 5 minutes and 80° in 20
• These milestones are similar to published wort recirculation results.

Test #3

• 57°F tap water through the large coil
• Followed by 45°F chilled water circulated with the Harbor Freight pump
• Continuous motorized stirring
• 28 minutes to cool 11 gallons to 62°F in Jan
• 140°F was reached in 4 minutes and 80° in 18

I think I’m on the right track. The real test will come next summer when tap water temperatures peak again. I’ll buy plenty of ice and update test results then.

When I reported on my new wort cooling build in the Strand Brewers' Club newsletter, The Dregs, I promised an update when the weather and tap water warmed up. On July 5, I brewed 11 gallons of Saison and cooled it from boiling to 68F in 35 minutes. 80F was reached with 72F tap water in 25 minutes and recirculated ice water did the rest of the work. This compares to a cooling time of 28 minutes for the same length brew in January when the tap water temperature was 57F.

Conclusions

An IC can cool 11 gallon ale batches to optimum pitching temperatures in much less than an hour. Key points are:

• Size the IC appropriate to your brew length.
• Start with tap water as the coolant. The large ΔT between it and hot wort allows quick cooling down to 80 or 90°F.
• Keep coolant flow rates high.
• Continuously stir the wort. This keeps warm wort and the IC in contact.
• Circulate chilled water as the last step. This is a powerful aid to fast cooling and low finishing temperatures.
• During this project, I came to the understanding that 80°F is the key wort temperature in the cooling process. Below 80°, the risk of infection is small and cooling to your desired pitching temperature can proceed with little fear of problems. Getting the bulk of the wort to 80° quickly is worth the effort to preserve hop character and limit DMS, wild yeast and bacteria’s effect on the beer.

Brewery upgrades are never finished. Even faster cooling is possible by:

• Tweaking the impeller size or shape to increase mixing while still avoiding the dreaded HSA.
• Running the coolant pump continuously to keep flow rate high.
• Using a cold liquor tank like some commercial breweries. Ice does have a big advantage over liquid water for heat absorption due to the latent heat of fusion as Mike Hall explained in HBD. Ice should be included in the final stage of the process for fast cooling to low temperatures.
• Using dry ice for water cooling. This might be more entertaining than practical. But hey, this is a hobby!
• Totally off topic, but this video of liquid oxygen being used to start a barbeque fire is a real hoot. Now that’s entertainment!

Improved FTC is my next project.

Thanks to Ron Cooper and Jim Hilbing for sharing their expertise and historical tap water temperature data.