The aim and benefits of a carefully conducted secondary fermentation are as follows [LN] [GAHM]
- achievement of final attenuation
- natural carbonation
- sensory maturation of flavor compounds
- clarification
- improvement of head retention
- excretion of unstable protein compounds
- improvement of colloidal stability due to the low temperatures
Transfer
Both, cold or warm classic fermentation schedules lead to the point in time where
- the temperature is between 3…5°C
- the residual fermentable extract is between 1,0…1,5%
- the fermentation slowed to a daily rate of 0,3…0,4%
Beer is then said to have attained its “Schlauchreife”, which is the point in time where a transfer to secondary fermentation tanks (often called “Lager” tanks) occurs. It is worth noting that an adequate amount of suspended yeast in the region of 12…15 million cells per ml should be present. Some brewers add a secondary yeast strain at this stage to ensure successful secondary fermentation and attenuation. Whereas during main fermentation a medium to highly flocculating yeast strain is used, a low flocculating strain at a ratio of 2:1…3:1 of main yeast strain to secondary strain sometimes makes its way into the secondary tank.
The cellar temperature where the tanks are situated is generally kept at 2…3°C. One of the reasons to bring the temperature of the main ferment close to this temperature is to avoid shocking the yeast, as well as conditioning the yeast to gradually handle the low temperatures at which it is expected to continue working in due course. [GAHM]
Transfers have an effect on fermentation as well, As the beer travels through the lines the yeast is set in motion again, which causes the fermentation to continue more vigorously. However, too vigorous is not desirable either. The aim of secondary fermentation is to gently and gradually continue the fermentation at low temperatures over a time-span of 4…8 weeks (pending on OG). Too strong a fermentation at this stage will cause the remaining extract to be consumed too quickly and lead to sub-optimal results. It is for this reason that Lager vessels are filled from below [LN]. When using home brew kegs this is simply done by filling via the outlet posts through the dip tube.
It is a well-known fact that beer is highly susceptible to oxidation during the cold phase and the transfer stage is no exception to that rule. Since fermentation is not complete, any residual oxygen left in the secondary tank is consumed. However, it is necessary to fill the receiving vessel to its maximum capacity in order to avoid too much oxygen remaining and damage the product.
Spunden
Once the transfer is complete, a pressure relief valve and manometer (“Spundapparat”) is connected and the pressure is set according to the desired degree of carbonation.
Typical CO2 content is between 0,48…0,52% for Bavarian Lagers. In order to achieve optimal carbonation the following values are recommended [GAHM].
| Duration/weeks | Temperature/°C | Pressure/BAR |
|---|---|---|
| 4…6 | -1…1 | 0,35…0,45 |
| 2…4 | 1…4 | 0,50…0,80 |
Temperatures
In his first book [LN], Ludwig Narziss goes to great length with a pedantic example on the temperature settings for each phase.
| Days | Temperature/°C | Remaining Extract/% |
|---|---|---|
| 0 | 4,5 | 1,3 |
| 3 | 3,0 | 0,9 |
| 7 | 2,7 | 0,7 |
| 14 | 1,0 | 0,5 |
| 21 | 0,0 | 0,4 |
| 35 | -0,7 | 0,3 |
| 49 | -1,0 | 0,2 |
| 63 | -1,3 | 0,1 |
References
- [GAHM] Gerolf Annemüller, Hans-J. Manger. Gärung und Reifung des Bieres (2. Überarbeitete Auflage).
- [LN] Ludwig Narziss, Abriss der Bierbrauerei (7. Auflage)
Hi Nico, your posts are very informative, and insightful as ever, thank you!
I have another question, if you wouldn’t mind. I have a Helles lagering, which I brewed to your traditional lager schedule. It has been lagering at 0.5 C for a week, and the SG is at 1.013 (OG was 1.052). Fast ferment test showed the expected full attenuation to be 1.011. Can I expect the SG to drop a little more towards full attenuation during lagering?
A brief summary of my actions:
-Pitched an estimated 1.5 billion yeast cells per liter of wort at 6C (WLP833) (into well aerated wort)
– Allowed temperature to free rise to 8.5C. Good signs of healthy fermentation with krausen formation in less than 48 hrs.
-fermented @ 8.5C for 5 days
-Dropped temp by 0.5C per day until reached 5C, then racked to secondary keg.
-started fermentation of extra beer to be added as Kräusen (equal to 10% of total volume)
-pitched Kräusen into secondary keg at 5C after 2.5 days fermenting.
-Dropped to lagering temps by 0.5C per day.
Beer has no detectable diacetyl or off flavours, but is still green and not mature of course. In your experience, will the FG drop further over the next month of lagering?
Sorry for the long question! I appreciate any advice or feedback. Vielen Danke!.
regards,
Nick
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Hi Nick
Thanks for the feedback. Please note that this is not my lager schedule but my online notes collected from professional textbooks (see cited sources).
There are a few things you could improve.
You used ten times less yeast than recommended and that you dropped the temperature way too fast during secondary.
0.5 day is way too fast for secondary once you approach 3 Celsius. This didn’t give the yeast any time to adapt or to complete fermentation of the residual extract. And it stalled despite the Kräusen added (I never bother with that BTW)
I am not sure you read my notes on secondary and conditioning. You may find it an interesting read 😉
Your FG may drop but it’s unlikely from what I gather.
I’d raise the temperature again to 5C, add more Kräusen (12%) and start over again.
This time I’d stick to the much slower temperature drop as outlined in http://wp.me/p4rkA1-f6
You want that very slow and carefully conducted secondary phase. It’s the same for warm and cold fermentation, that’s why my notes are on a separate page.
I’ve done this one several times over and it’s well worth getting to grips with it.
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Thank you for replying so quickly. I think I made a mistake in stating my amount of yeast. I used the yeast calculator at http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/ and pitched a total of 289 billion cells for my batch which is only 15 liters.
Having read your notes more carefully, I see that it should take approx 18 days to get from 3C to 0C….Oops! yes, it seems I rushed it and stalled the yeast. Apologies for not having read that properly the first time.
I will add fresh Kräusen as you suggest, and start again from 5C. I find it interesting that you omit the Kräusen yourself? Do you find it does not add much extra quality to the final result?
Should I pitch only the Kräusen liquid, leaving the yeast cake behind, or pitch it all, Kräusen and yeast?
Thanks again.
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Your cell count should be between 15-25 billion cells per litre. For 15 litres that’s 225-375 billion cells. I don’t need an online calculator to do that math 😉 It’s about 0.5 litres of slurry per hectolitre (100 litres). Easy enough.
The technique of adding fermenting yeast at its peak to the conditioning phase was initially used as an emergency/remedy for exactly the situation you are in now.
Over time, many brewers opted to add it routinely as an insurance policy. It’s not difficult to do when one makes the same batch several times a week and has plenty of supply in the fermenters. For people making occasional brews, I don’t see the need, though. I don’t want to take to time to mash and ferment just for that (it’s only 10-12% so that’s 4-5 litres for me), and doing it with spray malt or other would just introduce a different ingredient — which I don’t want.
Doing a secondary fermentation carefully will remove the need for this measure, so I don’t bother.
In the secondary phase, it’s not good to introduce too much yeast. If your fermenting batch is at it’s highest propagation rate then you have enough left in suspension and I’d pitch that only, omitting any sediment.
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Do you ever get diacetyl problems with such a low temp? Or any other off flavor?
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No, I don’t. Several of my mates do this as well and nobody reported off flavours like diacetyl. Your yeast needs to be in pretty good shape though. It’s not like we have to worry about the hydrostatic effect that occurs in a 6000 hl ZKV either.
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