Under Pressure: Getting into Pressure Fermenting

This month (June 2021), Steve Smith gave us an introduction to pressurised fermentation.

Transcript

1. Under Pressure Getting into pressure fermenting
2. What we’ll cover • What it is • How it works • What you need • What’s next Caveats: • Still need to pay attention to ◦ sanitation, temp control, mash pH, recipe • It’s not a magic bullet • It’s a work in progress
3. What is it? • Fermenting in a closed vessel using a spunding valve instead of an airlock • Capture or add CO2 during fermentation • Closed vessels: ◦ Corny keg, Fermzilla-type conical or stainless steel unitank, but never glass
4. Why you might want to try it • Speeds up fermentation, warmer temp means built-in diacetyl rest • Suppresses off flavours; fewer produced, cleaned up quicker • Retains more hop aroma • Keeps oxygen, bugs and dust out - good for all beer styles • Reduces krausen, more headspace • Self-carbonates, Reinheitsgebot-friendly • Ferment, carbonate and serve from the same vessel • Ferment clean tasting lager at room temperature, but can work for estery ales and phenolic Belgian/wheat styles too
5. Watch out for Too much pressure: • Yeast stress • Under-attenuation • Possible foam harm • Under-performance when repitching
6. It’s all about the yeast • We know yeast strains perform differently, different flavour profiles • Very useful, but need more than “All good” • Want to avoid “It works fine for me” • Not trying to do a grain to glass in 7 days • Want to find out how and why it works Source: David Heath Facebook Group (2021)
7. How it works - reducing esters and fusels • Science, numbers, lab data! • A highly recommended listen BeerSmith podcast episode #163 Jan 2018 - the one that got me into it John Blichmann/Chris White experiment to ferment a lager at room temp They split a batch and measured the compounds at the lab Source: Blichmann, White (2018)
8. How it works - reducing esters and fusels • Similar results to Blichmann/White • Very useful sensory demo • Highly recommended watch, nice cat • The Zythologist split a batch of pale ale: 18°C @ 0PSI vs 22°C @ 10PSI Source: The Zythologist (2021)
9. How it works - increase temperature • Higher temperatures > rapid yeast propagation. • Rapid yeast propagation > increase in the rate of esters (fruity) and fusels (hot, harsh) • Acetic acid + ethanol = ethyl acetate (solvent) • Acetic acid + higher alcohols = isoamyl acetate (banana) also isobutyl acetate (pineapple), and several more Source: The Zythologist (2021)
10. How it works - increase pressure • Yeast metabolism slows - due to concentration of CO2, rather than static pressure, per se • Esters are significantly reduced • Fusels are reduced, but by less Source: The Zythologist (2021)
11. How it works - increase temperature and pressure • Higher temperature increases ethanol, fatty acid, esters, higher alcohols • Higher pressure (higher CO2 concentration) decreases ethanol, fatty acid, esters, higher alcohols • Effects of temperature increase are balance or cancelled out by the increase in pressure • Result: faster, cleaner fermentation Source: The Zythologist (2021)
12. Even higher pressure: esters and fusels Above 15 PSI, up to 30 and 45 PSI • Esters continue to be reduced • Fusels are too • So why not ferment higher? Source: Renger, van Hateren, Luyben (1992)
13. Even higher pressure: yeast • At 15 PSI - yeast biomass is largely unaffected • At 30 PSI - 30% less yeast biomass to ferment and clean up of flavours • At 45 PSI - 70% less yeast biomass to ferment and clean up of flavours Source: Renger, van Hateren, Luyben (1992) • In stress situations the yeast produces yeast proteinase A, which has a foam-damaging effect - not clear what pressure that happens Source: Kunze (2004) Source: Renger, van Hateren, Luyben (1992)
14. The Master Slide Combined all the above sources in one table. Sweet spot is 10-15 PSI - balances yeast health and ester reduction
15. My settings and reasoning • Generally ferment at room temperature 20°C @ 12-15 PSI • Reasoning: if 15 PSI produces a clean lager as at 10°C, then an increase in pressure of 1.5 PSI has the same effect as a drop of 1°C ◦ Note: temperature does not actually drop when pressure is increased! • So, for a pale ale, 3 PSI = drop of 2°C from 20°C to 18°C • For a saison, 3 PSI = drop of 2°C from 29°C to 27°C • Overbuild starters rather than repitch on previous yeast cake – investigating the effect of repeated pressure ferments on the same yeast cake • Pitch yeast as you normally would, eg, double sized lager pitch to compensate for suppressed yeast growth
16. When to set the pressure These options are for a lager style. • 15 PSI from the start - close up the FV and pressurise, leave it until FG • 0 PSI from the start - set spunding valve to 15 PSI and let pressure build • 0 PSI until after primary fermentation is a few points from terminal, to self-carbonate the beer • Spunding from the beginning as a safeguard to control the esters as well as the ester precursors ◦ Especially important for lagers as warmer fermentation produces more esters
17. Accelerated maturation and lagering To investigate: • Does the reduction in esters and fusels mean maturation and lagering can also be faster? • Is there more to lagering than slow, cold chemical reactions - complex and unclear? ◦ To do: read The Biochemistry of Maturation (1986) - Masschelein
18. Summary of my settings for different styles • After pitching yeast, set the spunding valve to the PSI shown • A lower PSI allows more esters and phenolics through Beer style Actual temperature Spunding valve setting Temperature equivalent Yeast tested Clean German/Czech 20°C 15 PSI 10°C W34/70, WLP860, M76, Imperial Urkel, WLP800, M84 Hoppy American IPA 20°C 3 PSI 18°C US-05 Estery British ale 20°C 3 PSI 18°C - Phenolic Belgian saison 29°C 3 PSI 27°C BE-134, Blaugies Wheat beer 20°C 6 PSI 16°C -
19. Dry hopping a pale ale/IPA under pressure • Set to 3PSI from the start • When 1 or 2 points from FG, release the pressure slowly, remove lid • ‘Quietly’ drop in hops • Replace lid, purge headspace with CO2 • Increase spunding valve to 15 PSI - timing is crucial to prevent off-gassing of any hop aroma! • Cold crash, keg, force carbonate • Do not dry hop well-carbonated beer… dry hop volcano!
20. Other yeast • I’ve had consistent, great results with W34/70, US-05, yet to try S-04 ◦ All yeast strains need careful handling as usual • High pressure yeast - not used it, but similar specs to W34/70 in terms of temperature range, attenuation • Kveik - not used it, but use the previous chart to pick a PSI for the ester level you’re after • Calculate your own pressure vs ester level for a given yeast strain
21. What you need - you may already have the basics CO2 cylinder £50 deposit, £36 refills Regulator £60 A fridge for temperature control £20 off eBay Gas line, disconnects, connectors £30 Dispense: party tap and 10ft of 3/16in tube £10 Bottling: DIY carbonation cap adaptor for PET / beer gun / counter pressure filler £10 / £50-100 /£30- £100+
22. What you need - Corny keg kit Reconditioned keg £55 Floating dip tube with gas tube £16 Floating dip tube filter to weigh down the end and block hop bits £3.50 Spunding valve Blow tie £30 Spundit 2 £80 Total: £105+ Never use the PRV on a corny keg as a spunding valve
23. What you need - ‘Fermzilla’ kit Cylindro-conical shape is useful for dumping trub and collecting yeast (base price +pressure kit) Fermentasaurus (£99 +£29) Fermzilla (£124 +£19) Allrounder (no dump valve) (£68 +£19) Spunding valve £30 Total £117 to £173+
24. What you need - SS Brewtech unitank SS Brewtech Unitank 7 gal £1,170 to 1BBL £1,850 Or a fast getaway driver - priceless Total: £2,000+
25. Oxygen-free transfer • Any style can take advantage of fermenting under a small amount of pressure to keep out oxygen, bugs, wild yeast, dust, sneezes • Purge keg with StarSan • Equalise pressure in FV and keg • Increase CO2 by 1 or 2 PSI for a gentle transfer, or slightly open spunding valve to regulate flow
26. Next steps - improvements and further study • Tighter temperature control, especially after fermentation; get finished beer in the fridge (if not already) to prevent further off flavours developing • Lager at -1°C to accelerate lagering for fresher beer ◦ -1°C for a week about the same as 2°C for a month ◦ Investigate whether lagering can be accelerated • Overbuild starters instead of dumping on previously pressurised yeast cake • Solve pH measuring issue, mine is too high. Should it be measured at mash temp (when it should read 5.2) or room temp (when it should read 5.5)? • Investigate oxygen levels for different bottling methods: party tap, beer gun or counter pressure vs brewery standard ◦ Brulosophy study finds little difference when capping on foam
27. Takeaways - a four-pack • Produces cleaner beers of all styles, especially lagers • Faster fermentation, gear is tied up for less time, can make more beer • Keep oxygen out for a longer shelf life, especially for hoppy beers • Relatively affordable, especially if you have some gear already Question time!
28. References • Pressure Fermentation (2018) - BeerSmith podcast episode #163 with John Blichmann and Chris White • Yeast Under Pressure (2021) - The Zythologist YouTube • The Formation Of Esters And Higher Alcohols During Brewery Fermentation; The Effect Of Carbon Dioxide Pressure (1992) - Bv R S Renger, S H van Hateren and K Ch A M Luyben • Esters and Fusel Alcohols (2016) - Scott Janish • Fermenting & Dry Hopping Under Pressure (2016) - Scott Janish • The Biochemistry of Maturation (1986) - Charles A Masschelein • Technology Brewing and Malting (2004) - Wolfgang Kunze • David Heath Facebook group (2021) • Flushing with CO2 vs direct filling when bottling beer from kegs (2017) - Brulosophy • Kegging with care: a guide to purging (2018) - The Modern Brewhouse • Lots of blogs and YouTube channels, including The Home Brew Network, Larry BBQ, Dr Hans, David Heath - some I used more than others