Last week we installed our new sour tank! A 750 gallon (~23 BBL) stainless IBC from Custom Metalcraft, this new tank has allowed us to double batch kettle sours. Previously, when brewing a kettle sour, we could only brew 10 BBLs–the size of our kettle–at a time. We opted for a small customization of a 3” rather than 2” port on the top to accommodate a Stout spray ball/tri-clamp adapter we already had, but otherwise it is a simple square tank with no insulation or cooling.
The plan was to suspend the tank up above the brewhouse so that we could gravity-feed it back to the kettle for pasteurization/whirlpool additions and avoid running bacteria through a pump. We took some metal shelving and cut and welded the crossbeams to be the right size for the tank, along with some additional pieces for reinforcement. We put the shelving in place, and then lifted the tank up into place with a chainfall, using straps to pull it out and then over the shelves. After setting it down, we strapped the tank down with ratchet straps, put some 6×6’s underneath the legs of the tank for additional support, and chained the uprights to the nearby building upright. This amount of additional reinforcement could support several more tons than the weight of the filled tank, so we felt safe.
The process worked like a charm. We knocked out two batches of our sour IPA into it at 100 degrees, pitched a big starter of lactobacillus plantarum, and hit our target PH 36 hours later. I would like to cut this time down but I am OK with it for now. The soured wort had zero off-flavors or aromas. Once we hit our PH, we did exactly as planned, draining 10 BBLs at a time to the kettle for pasteurization and a big whirlpool addition of Mosaic hops.
After draining, I hit the tank with some 180 degree water from our HLT through the spray ball we hooked up to the top. I took the sample valve on the side off before to make sure the tank could vent steam adequately. They cannot hold much pressure, so I was a bit worried about this, but it was fine. After hitting and draining it repeatedly, I felt satisfied that everything was dead inside and proceeded to run a cycle of hot caustic. Afterwards, I rinsed with ground water. Here is where I nearly messed things up. The cooler ground water immediately created negative pressure, and the sides of the tanks started shuddering. I only had it on for a half second before I cut it. Next time I will start it very slowly. A bit of rinsing and a visual inspection later, and the tank was mirror clean–the key to a good kettle sour.
Some key parts to our process.
- Your souring vessel needs to be absolutely clean. Kettle sours are very risky because the beer is not protected against unwanted yeast and bacteria during the souring process. That is why a separate tank is superior to your kettle. It’s hard to get your kettle as clean–there are way more ports, vents, etc, plus the buildup on your kettle is hard to remove completely. The secret to success is a clean vessel.
- You need to hit your target PH as quickly as possible. You cannot add too much healthy lactobacillus. Make a big, healthy starter a day or two beforehand. The more time your beer spends unhopped without yeast, the more likely it is to become wrecked by unwanted stuff.
- No pre-acidifying, no CO2 purge. There are acid-tolerant strains of Clostridium bacteria, so pre-acidifying your wort to 4.4 or under isn’t a total safeguard, and the idea that it aids in head retention is asinine to me since I always use lots of wheat, rye, or milk sugar which aids in body. Furthermore, the point of kettle souring is to avoid adding food grade lactic acid to your beer. But the big one so many people swear by is the CO2 purge. There is no purpose to this. Clostridium, the main culprit in ruined kettle sours, are anaerobic. So purging does nothing. Lactobacillus only creates off-flavors in heavily oxygenated wort, so some air in the head space is not going to do anything bad in that area, either.
- You can really crank your yeast after a kettle sour since PH suppresses esters. I let mine run to 76 and our yeast seems to really love acid beers, absolutely ripping through them. So even with the souring, the turn time is really fast.
So that’s our process. I’d like to also take a minute to talk about what makes a good kettle sour.
First, a kettle sour is a kettle sour. Sounds obvious, right? Well, a kettle sour is not just made by adding food grade lactic acid to a beer or using acid malt. Every beer I have had made this way has been obvious and disappointing. Beers either are not sour enough or have a harsh, throat-burning sensation. Unfortunately, many breweries are passing these beers off as sour beers.
Second, a kettle sour should never have a cheesy or vomit-like aroma or taste. Man, oh man, are there a lot of offenders here. I do not want to name names, but some big, respected breweries have put out some very bad kettle sours that should have been dumped. Uneducated consumers don’t seem to notice as much as one would hope, maybe writing these flavors off as “funk,” but these are unpleasant flavors that should not be tolerated.
Making good sours isn’t extremely difficult, but it does require more sanitation and care than a regular beer. Our fast sours are clean, and we also use a lot of real fruit. They’re some of my favorite beers we make. If you’re planning on making one, again, the key is clean real estate, big starter, fast sour. Do that and all will be well!