Culturing Lactobacillus from Commercial Yogurt for Brewing Kettle Sours Serge Savin / LAB / November 2019 

Why bother? • Additional technique in your brewing arsenal • Save a bit of cash - £2 vs £7 for a commercial culture • Availability – nearly all supermarkets stock ‘live culture’ yogurts • Produce a range of interesting (and not so much) flavours • Justify getting an expensive toy! 

Kettle Souring • Bring wort to boil for 5 minutes (no hops), to kill any unwanted yeast / bacteria • Cool wort down to temperature appropriate for your lactobacillus culture – can be between 20-43C! • Acidify wort down to 4.2-4.3 pH, to aid head retention • Pitch your lactobacillus culture • Create airtight seal (pumping CO2 is optional) • Take pH measurements every 12hrs • Boil as per intended recipe, adding hops, etc Rough pH level descriptions: • 3.6 – somewhat sour • 3.5 – noticeably sour • 3.4 – prominently sour • 3.3 – considerably sour (Gueuze) • 3.2 – mouth-puckering-but-oh- so-good sour 

Lactobacillus • Rod-shaped lactic acid bacteria (LAB), over 150 species, many can be found in the digestive system • Often used in production of yogurt, kefir, pickles and sauerkraut • Used to ferment Berliner Weisse, Lambics, Gueuze, Gose and many sour ales • Different species metabolise different types of sugars for growth, including sugars that Saccharomyces may not be able to ferment • Produce acidity and sour flavours in the form of several types of lactic acid and a range of secondary metabolites (hence flavours vary by strain!) • Two categories of metabolism: • Homolactic – fermentation produces only lactic acid • Heterolactic – fermentation produces lactic acid, CO2, and ethanol/acetic acid 

Selected Commercial Yogurts YOGURT LISTED LIVE BACTERIA Yeo Valley Natural L. acidophilus Streptococcus thermophilus Bifidobacterium lactis Yeo Valley Kefir L. acidophilus L. bulgaricus L. delbrueckii subspecies lactis L. fermentum L. paracasei L. rhamnosus Lactococcus lactis subspecies cremoris Lactococcus lactis subspecies lactis biovar diacetylactis Lactococcus lactis subspecies lactis Leuconostoc mesenteroides Leuconostoc pseudomesenteroides Streptococcus thermophilus Bifidobacterium infantis Bifidobacterium lactis YOGURT LISTED LIVE BACTERIA Onken Natural Set L. acidophilus Streptococcus thermophilus Bifidobacterium lactis Yakult L. paracasei Shirota (first isolated from the human intestine by Japanese scientist Minoru Shirota in 1935!) Kefir Quark L. acidophilus L. plantarum L. casei L. rhamnosus Bifidobacterium lactis The Coconut Collaborative L. bulgaricus L. acidophilus S. thermophilus Bifidobacterium lactis 

Testing Process • AIM: find out which yogurt culture provides the highest drop in pH, consuming the least sugar • Make a DME starter (1.035-1.040) • Sanitise everything! • Add equal amounts by weight (120g) of yogurt to starter wort (750g), shake • Ideally, hold in the 38-43C range for optimum growth, but these experiments were done at 31-32C • Experiment 1 – 8 days, 1.034 OG, 6.64 pH • Day 2 – visual observation • Day 8 – visual observation, aroma and flavour test, gravity reading, pH reading • Experiment 2 – 3 days, 1.042 OG, 6.64 pH • 36 hrs - visual observation, aroma test, gravity reading, pH reading • 72 hrs - visual observation, aroma and flavour test, gravity reading, pH reading 

Experiment 1: ‘Eliminator’ – Day 2 YOGURT pH (ORIG. pH 6.64) WORT COLOUR CLARITY FERMENTATION SIGNS? Yeo Valley Natural 4.11 Dark Clear None Yeo Valley Kefir 3.50 Very light Hazy None Onken Natural Set 3.95 Dark Clear Visible carbonation, foaming Yakult 3.57 Medium-light Clear None Kefir Quark 3.42 Medium Clear Visible carbonation, foaming The Coconut Collaborative 4.60 Very dark Clear Visible carbonation 

Experiment 1: ‘Eliminator’ – Day 8 YOGURT GRAVITY (OG 1.034) pH (PREV pH) WORT COLOUR CLARITY FERMENTATION SIGNS? AROMA FLAVOUR Yeo Valley Natural 1.010 3.57 (4.11) Medium-light Clear Huge gas release, foaming Clean, milky sour, pleasant Sour, sweet milk Yeo Valley Kefir 1.033 3.42 (3.50) Very light Clear None Malty, clean, sour, pleasant Very sour, almost salty, hint of milk Onken Natural Set Forgot to measure, <1.010.. 3.64 (3.95) Medium Clear Fountain explosion Cheesy Cheesy Yakult 1.028 3.41 (3.57) Medium-light Clear Explosive gas release, foaming Mildly sour, grassy-sweet smell, very interesting Sour salty candy, hint of milk Kefir Quark 1.032 3.34 (3.42) Medium-light Clear Slight gas release, no foaming Malty, hint of sourness Very clean salty sour, hints of curd The Coconut Collaborative 1.032 3.99 (4.60) Dark Clear Slight gas release, foaming Stewed chickpeas, rancid Stewed chickpeas, rancid 

Experiment 2: ‘Verifikator’– 36 hrs YOGURT GRAVITY (OG 1.042) pH (ORIG. pH 6.64) WORT COLOUR CLARITY FERMENTATION SIGNS? AROMA Yeo Valley Natural 1.038 4.29 Medium-light Clear Touch of gas release Clean, malty, a touch sour Yeo Valley Kefir 1.038 3.83 Very light Clear None Clean, malty, sour Yakult 1.042 3.83 Medium Clear None Mildly sour, grassy-sweet smell, very interesting Kefir Quark 1.042 3.76 Light Clear None Malty, hint of sourness 

Experiment 2: ‘Verifikator’– 72 hrs YOGURT GRAVITY (PREV GRAVITY) pH (PREV pH) WORT COLOUR CLARITY FERMENTATION SIGNS? AROMA FLAVOUR Yeo Valley Natural 1.030 (1.038) 3.86 (4.29) Medium-light Clear Noticeable gas release, foaming Clean, malty, touch sour Milky, powdery, sharp sourness Yeo Valley Kefir 1.032 (1.038) 3.66 (3.83) Very light Clear Slight gas release, slight foaming Clean, lactic sourness Assertively fruity Yakult 1.042 (1.042) 3.61 (3.83) Medium Clear Moderate gas release, moderate foaming Mildly sour, grassy-sweet smell, very interesting Fruity, pineapple juice, milky sour Kefir Quark 1.040 (1.042) 3.49 (3.76) Light Clear None Malty, hint of sourness Sharp lactic sourness, cheesy, tangy 

Gose: ‘Eksperimentator’ • 12.5l batch, 4.2% ABV, 3.2 CO2 Vols • 65C mash, 15 mins boil, 21C ferm. • Water: • Ca 105 | Mg 9 | Na 38 | SO4 61 | Cl 70 • 0.87 - SO4/Cl ratio • Grains: • 60% Weyermann Pale Wheat • 40% Weyermann Barke Pilsner • Hops & additions: • 6.6 IBU Hallertau Magnum • 9g freshly crushed coriander • 7g sea salt • 250ml Yeo Valley Kefir • Wyeast 1007 German Ale • 5.25 pH – mash • 4.20 pH – after acidification with lactic acid • 3.47 pH – after souring for 24hrs, temperature drop from 42C down to 35.4C • 3.52 pH – post boil • 3.49 pH – after carbonation • Specific gravity: • 1.040 mash • 1.040 after souring stage • 1.042 post boil • 1.010 final 

Conclusions • Using yogurt for kettle souring is a perfectly viable alternative to commercial lactobacillus cultures • Not all yogurts are equal: • While all contained lactobacillus, several cultures consumed a lot more sugar than others • Onken Natural Set and Yeo Valley Natural listed as containing only L. Acidophilus, Streptococcus thermophilus and Bifidobacterium lactis • Yeo Valley Kefir and Kefir Quark, had several more, yet did not experience such a dramatic drop in gravity over an 8 day period • Could possibly point to yeast contamination from the factory • This could be utilised for brewing low alcohol beer, Yeo Valley Natural did not produce any off flavours while eating through considerable amount of sugar, while retaining medium-full body and malty characteristics • Starting temperature and pH play a role – Gose soured with Yeo Valley Kefir at starting temperature of 42C and 4.2 pH did not experience a drop in gravity and reached 3.5 pH within 24hrs, vs the same culture at 32C and 6.6 pH • Making a souring culture starter isn’t necessary at high concentrations, suggested dosage for Yeo Valley Kefir is 250ml / 15l wort • Yeo Valley Natural, Yeo Valley Kefir and Yakult have produced a set of distinct aromas and flavours, which could be creatively used!