Kettle Souring with Lactobacillus

I started brewing beer a little over a year ago, and it has become a mild obsession. As my journey with brewing has progressed, so too has my exploration of craft beer, albeit for inspiration if not because so much of it is really f*cking good. I stumbled upon sour beers and it was love at first sip. I’ve never been much for IBU-packed IPA’s or smoky stouts. My palette has always erred on the lighter, fruitier, aromatic side of beer. Saisons, Pales, NE IPA’s, and once I discovered them, sours have quickly taken up all of my highest ratings on Untappd as well as my storage space.

I first read about kettle souring in Michael Tonsmeire’s book American Sour Beers. It’s an appealing sour method because it takes less time than long term sours, and depending on how you do it, you run much less of a risk of infection and can reuse virtually all of your equipment. Probably the biggest con for kettle souring is that it does take a LOT of equipment to get right that most homebrewers don’t have when they’re first starting out. But I made up my mind and decided to give it a shot… and failed miserably. The first time. The second attempt actually turned out pretty well, though there are still plenty of things I’d do differently next time — but I feel that way about every beer I brew.

This post is split up into two parts, Lacto Lab #2 and Lacto Lab #1. I’m going to explain the second attempt first because the first one was gross enough that if you read it first you’d probably stop there. I’m still relatively new to the brewing scene and there are a myriad of ways to create a kettle sour; this documents the steps I took to create one that turned out. And one that didn’t

Lacto Lab #2

A kettle sour is a quick-souring style that takes a fraction of the time of a regular sour to achieve the same tartness. Many brewers feel that kettle sours aren’t nearly as complex as regular sours, and after drinking my fair share of both types, I don’t disagree. But that’s not to say that kettle sours aren’t a worthwhile endeavor. Kettle sours are significantly cheaper to produce because they take so much less time to make. You don’t need nearly as much storage space, and the feedback loop for flavor profiles is faster, so it’s less risky to experiment. And even if they are less complex, they still taste really good. Sours get their tartness from wild yeast and bacteria (usually Lactobacillus, Pediococcus, and/or Brettanomyces, as well as some strains of wild Saccharomyces) that eat the sugars in a wort and produce lactic and/or acetic acid. Regular sours take so long to produce because most brewer’s yeast has a higher metabolism than sour yeast / bacteria and will eat all the readily available sugars in the wort, leaving only the longer chain carbohydrates (harder-to-digest sugars) for the sour cultures, which take longer to digest. Slow metabolism plus difficult-to-digest food source equals a long time to sour. The kettle sour method aims to speed up the process first by giving the souring yeast / bacteria exclusive access to the wort (food source) by pitching the culture without the brewer’s yeast, and second by heating the wort up to increase the metabolism of the culture. In the right environment, a sour culture from a starter can sour a carboy full of wort in 1–3 days. Sour mashing is the same concept except you leave the grains in the wort after mashing. I found kettle souring to be easier because I don’t have an airtight mash tun (I use a pot wrapped in a blanket to mash).

The first thing required to successfully kettle sour is the equipment. You will need:

• (Optional but recommended) Erlenmeyer flask with stopper and airlock, and stir plate for regular yeast starter. Don’t use the stir plate on the sour culture starter, stir plates are for oxygenation and you don’t want oxygen in a sour starter.
• a way to heat up your wort to ~110 degrees F in an anaerobic environment (i.e. no oxygen). I used a 5 cu ft chest freezer, 7.5 gal carboy with an airlock, a temperature controller, and a reptile heater (NOTE: A ceramic heater will not work for this warm of a temperature. I tried a few different brands and they all have emergency shutoff switches that trigger at ~85 degrees F. The reptile heater was able to keep the carboy perfectly warm in the chest freezer). Plug the freezer into the cold feed, the reptile heater into the hot feed, and the temperature controller into the wall. I set mine to have 1 degree F accuracy with a 10 minute offset so I don’t blow out my freezer compressor. I also keep a dehumidifier in the freezer because moisture buildup does become a problem at these temperatures.

My fermentation chamber

You will also need a recipe. I was attempting a kumquat ginger gose:

• 5 lbs US 2 Row + 2 cups uncrushed for sour starter
• 6 lbs White Wheat
• 1 package Lactobacillus Brevis
• 1 package WLP001 or WYeast 1056
• 1 oz Tettnang hops (@60min)
• 1 oz coriander (@15 min)
• 1 oz salt (@15 min)
• 4 lbs kumquats (~4 weeks)
• 1 pint vodka (for the ginger tincture)
• a few medium-to-large pureed ginger roots (for the ginger tincture)

First, I made a starter using Five Blades Brewing’s Lactobacillus starter method. It varies from a normal starter in a few key ways. It’s airtight (stopper and airlock) instead of loosely covered with foil, lactic acid is manually added to decrease the pH and help the bacteria thrive, uncrushed malt is added, and it’s topped off with carbonated water to purge the head space of oxygen (keeping oxygen out of your fermentation environment is the most important part of this process). I put the flask in my fermentation chamber on the reptile heater for 3 days (Next time I think I would leave the starter for less time — maybe 2 days— it soured much more quickly than I thought it would). I insulated the temp controller’s thermometer against the side of the flask with a towel to make sure I was getting an accurate reading from the starter itself instead of the ambient temperature of the fermentation chamber.

sour starter ingredients and equipment

When the starter had built up my culture for long enough, I heated up my mash water and mashed my grains at 150 degrees F for 60 minutes. I then boiled the wort for 15 minutes and cooled it to 110 degrees F. I poured the wort into a carboy, and poured the lacto starter into that, straining out the crushed malt. I then purged the head space with CO2 by putting dry ice in a funnel and letting the evaporating CO2 fall into the carboy and push the air out. If you have kegging equipment you can also blast the carboy with your CO2 tank.

purging the headspace of the carboy with CO2

Once the headspace was sufficiently purged, I put an airlock on the carboy, and put that into the fermentation chamber for 3 days at 110 degrees F.

Left: Lacto Lab #2, Right: slow soured raspberry framboise inoculated with WYeast’s lambic blend. It sat in my basement on raspberries and oak for 5 months.

When it was sufficiently sour, I pulled it out, boiled it for 60 minutes with hops, salt, and coriander. Once I the wort had boiled for awhile, I began to treat it as I would in my regular brewing process. At this point it had been pasteurized and was innocuous. I cooled the wort off, put it in a fermenting bucket pitched my WLP001 (1.5 L starter on stir plate for 24 hours), and put it back in the fermentation chamber at 67 degrees F. I let it go for 4 weeks and added 4 lbs of sanitized, cut, and frozen kumquats. I let it go for another 2 weeks on the fruit before bottling.

kumquats floating on the top of the beer

A week prior to bottling, I made a ginger tincture by pureeing a bunch of peeled ginger and putting it in a mason jar with a pint of wheat based vodka (I figured keeping the vodka close to the grain bill would have the least effect on the flavor), shaking it every time I looked at it. I then strained it through a sieve and the result was a super strong and spicy ginger tincture. I blended this with the bottling sugar on bottling day.

OG was 1.04, FG was 1.004 (though the pint of vodka probably added a decent boost to the ABV). I opened a bottle after 2 weeks and it had carbonated really well. It had great tartness and acidity, but the kumquat didn’t come through quite like I wanted or expected. That said, the ginger really saved it and it ended up being a very good and drinkable beer, especially after mellowing for another month. Lacto Lab #2 was a success and was dubbed ‘Come Quietly’ by my girlfriend Jenna, who deserves plenty of credit in the brainstorming and motivation for this beer and its ingredients. The ginger was her idea and it totally saved the beer by balancing out the tartness from the kumquats.

So, You’re probably wondering at this point, what happened to Lacto Lab #1? If you’re squeamish or bored feel free to stop here. If you like scary movies, read on!

Lacto Lab #1

When I first decided I wanted to try and brew a kettle sour, I didn’t have a fermentation chamber or an Erlenmeyer flask or know how to purge a carboy without kegging equipment (or exactly how important that part was). My starter was a 22oz bottle with an airlock at room temperature. I had this crazy idea that you could do the kettle souring part with a sous vide. I let the starter go 3 days, then made the wort (no preboil). I pitched the ‘starter’, plugged in the sous vide, set it to 120 degrees F, and and let it go.

Bottom Left: notes, sous vide, starter, Top Left: sous vide in wort, Top Right: Jenna stirring wort with the paddle

3 days later the wort’s tartness was barely detectable and it had an… off…? flavor. But I’d read about off flavors coming from sour cultures and that being okay because the yeast would reabsorb the off-tasting compounds over time. So I pressed on. Or rather my roommate Mitchell did. I went on vacation. He pulled samples every day I was gone for the next few days and I’m really glad he didn’t die because when I came home this was growing around the edges of the pot.

I made dis

I immediately threw the batch out. But not before the Dark Lord Cthulhu breached the surface.

The Dark Lord, Cthulhu

You see, the sous vide heated the wort up making it perfect for bacteria to grow and then oxygenated it by circulating the liquid. As this mold grew, the circulating water peeled it off in layers until it joined together and became a tentacled monster that was just heavy enough to sink and breach in the wort. Needless to say, I screamed, peed a little, cried a lot, and threw the whole batch out along with enough bleach and boiling water to kill whatever was growing inside it. Everything plastic that touched the wort went in the trash. Everything glass and stainless was furiously boiled and vigorously sanitized. My kitchen became an autoclave.

I was bummed and to be honest a little scared, but also interminable. I wrote a post mortem examining every aspect of my process and what I could do differently next time. Here’s what I came up with. It may be a good spot to start troubleshooting if you run into problems on your first try.

There were a lot of problems with my first approach, but the most egregious was allowing oxygen into my fermentation environment. I built the fermentation chamber so that I could control the temperature of the wort in an anaerobic environment, and made a bunch of other changes to my process (including calibrating my thermometer which is why my efficiency was so low the first time). Lacto Lab #2 went much more smoothly and yielded something worth drinking. There are plenty of things I would like to change about it (less kumquats for one), but it’s a solid start.

I hope this article helps those who are interested in kettle souring, or who are troubleshooting any gruesome brewing mistakes, or at least that it was entertaining. For more information on where to start, check out my post mortem as well as my resources for this article below. Happy Brewing!

Sources

• Sour Beer Blog — Brewing a Gose
• Sour Beer Blog — Lactobacillus 2.0 — Advanced Techniques For Souring Beer
• Sour Beer Blog — Fast Souring With Lactobacillus
• SeriousEats — Fast Sour Beer Recipe
• Milk the Funk Wiki — Wort Souring
• Five Blades Brewing — Lactobacillus Starter Guide
• American Sour Beers, Michael Tonsmeire
• Purging Carboy Headspace Without Kegging Equipment