Czech Lager - The Bridge v2!

This is a repeat brew day. Exactly the same kit, the only difference is that I extended the primary fermentation time.

Notes

Brew Day

I properly cleaned the fermenter before starting — twice, to be sure.

I’ve not got a lot of pictures from this brew day, it was really smooth again hot side. No issues at all.

My OG was 1.044. It finished a point drier this time at 1.006. Resulting in 5.1% ABV.

Fermentation graphs below have been smoothed - attached them via Brewfather too. OG was at 1.005 due to some trub on the pill seemingly.

Progress

The v1 post covered the first batch, which had acetaldehyde on transfer. After 12 days of fermentation here, which is the recipe guideline, I tried the beer and there it was again.

It’s worth noting that I had ~3psi of pressure on the spunding valve as the ferment was finishing, just to prove I had no leak/oxidation risk. This has gone down very slowly but only due to absorption, I’ve kept it topped up but low to be absolutely sure zero oxygen contact.

I left it stable at 12c. The acetaldehyde was still there at 20 days.

As of writing this blog post, it’s been in primary for 30 days. Still lingering acetaldehyde. Today, I decided to rouse the yeast with CO2. That’s when I worked it out — I realised what I’d done wrong on both of these batches. This is a lager yeast, it bottom ferments. I’ve had the yeast collection valve open on both of these ferments. The yeast cake has been trapped in a narrow collection vessel at the bottom of the tank meaning the majority of it has little/no contact with the wort. My problem has been stressed yeast/poor yeast health.

Maybe not conventional, but I lifted the fermenter up, released the full yeast cake back into the main vessel and then closed the valve, so that it would settle back down with more surface area and the yeast can do its thing. I had actually started the D rest but decided to drop back to 12c for a few days.

After rousing the yeast and completing the D rest, the beer did finish. It’s better than v1 — but only marginally. The yeast stress had already done its damage before I found the root cause.

The problem on both batches was the same: the yeast collection valve was left open throughout fermentation. The yeast cake gets trapped in the narrow collection vessel at the bottom, with little contact with the wort. Stressed yeast, and the acetaldehyde that comes with it.

The fix for v3 is simple: close the valve from the start on any lager ferment.

The first batch keg has mostly cleared in the keg and is drinkable — not perfect, but good enough. I don’t regret the repeat batch; I enjoy the lager brew day and the decoction process. Certainly learnt a lot to take forward.

Progress photos