Let's start this with the story of how I stumbled on this technique and why I can't shut up about it now.
If you've ever visited Czechia (aka the Czech Republic) and experienced their Pilsners, you'll quickly realise that they're absolutely nothing like what exists here in North America. What's missing is the burst of noble hop aroma that is, at best, muted and most of the time, completely absent. I even ended up purchasing a Lukr tap just to see if that was the cause and although it helped somewhat on the draft system, the Czechs seem to still preserve that hop aroma in their bottled Pilsners as well.
This meant I had to focus my search elsewhere and I settled on eliminating oxygen from my lagering tank. I use a 10g SS Brite Tank, but you can use any closed, pressurised container for this part. I regularaly purged the tank of oxygen, using the fill-with-sanitizer-and-push-out method but the hop aroma kept disappearing over the 4 weeks it took to clear.
This means that oxygen wasn't the problem, or at least not the sole problem. I decided to go back to tradition and think of lagering as a part of fermentation rather than simply cold crashing and calling it "lagering" as we do nowadays. The original point of lagering was to clean up acetaldehyde and diacetyl over a long period in cold storage. The thing is that cold storage wasn't sub-zero like we do now, but a gentle 4°C- 10°C. Over this time period, the yeast will not only reduce oxygen to zero, but also (somehow) preserve and protect the hop aromas from at least some of the aging processes. It appears that yeast - as long as it remains alive - is the elixir of youth for beer.
As for the process:
- Add a generous portion of hops as a whirlpool addition. Whole leaf appears to work better than pellet, possibly because polyphenols play a role in this as well.
- Reserve a portion of the wort for the lagering tank/pressurised vessel. The exact amount doesn't matter because carbonation is irrelevant at this point.
- Pitch the same relative quantity of yeast or more into the lagering tank as you do for the primary fermentation. Standard lager pitch rates are 2 million cells/mL/°P
- Ferment the lagering tank slightly higher - around 15°C. If using a proper lagering yeast, the extra esters will be negligible as lager yeast doesn't produce that many to begin with. Higher alcohols will be negated by the lower amount of wort and generous pitch rate. What the higher temperature will do for you is speed up the α-acetolactate > diacetyl > 2,3 butanadiol reaction.
- You will have to depressurise the tank at least once if you did it right as the yeast will stop if the pressure gets above 10 psi.
- After a few days, start dropping the temperature, but don't go below 4°C. You don't want the yeast to stop completely.
- Allow your primary fermentation to finish. I budget 2 weeks for this.
- Pressure transfer your primary fermentation into the lagering tank/pressurised vessel.
- Wait 4 weeks for the yeast to clean up and flocculate out. It may take longer if you're using a corny as the settling distance is greater than a wider, shorter vessel.
- Alternatively, you can filter. I'll be doing an article on filtering shortly.
That's it. Often we romanticize traditional methods even if they don't fit anymore, such as 6 hour mashes or triple decoctions using already well-modified malts. This appears to be at least one case in which traditional is simply better and I highly encourage you to try it out yourself and see the difference.