Post #1 made 8 years ago
I am currently fermenting a Vienna Lager and am considering what to do regarding a Diacetyl rest and lagering and am hoping I can get some advice/input.

I have looked at "How to Brew" by JP and "Brewing Classic Styles" JZ&JP and I have also seen some old threads in BIABrewer and I think between the three sources I understand but :think:

If I have it right, the techniques are started at about 3/4 way into primary fermentation and continue until fermentation finishes. A D rest is optional depending on ferment temp. With Lagering you can leave it in the fermenter once its finished or bottle and then lager for an extended period the length of which depends on what temp you are Lagering at, the cooler the longer. With a D rest you stop once ferment is finished and then bottle and then lager.

BCS says ferment at 10c for the entire primary ferment then bottle and then lager for a month or more, unless you fermented warmer... then you should do a D rest but it doesn't specify what 'warmer' is. HTB says..." ferment between 7-13c to inhibit fruity esters." So i take this to suggest a ferment above 13c requires a D rest? If you ferment lower a D rest is not required and you can go straight to Lagering? BCS seems to skip over Lagering for the final 1/3rd of the primary ferment.

I pitched at 11.5c at about midnight, the controller was set for 10c and it was 10c when I checked in the morning. I then checked HTB and got confused as it said ferment at 11c not 10c ( it seems BCS was where I read ferment at 10c) so I upped it and there it has stayed for 8 days.

There are two batches one has s23 yeast the other 34/70.

So I think i can skip the D rest and either leave it to ferment out at 11c and then bottle and lager or reduce the temp and ferment out at the lower temp then bottle and then lager.

Appreciate any input or pointers to relevant threads.

Last edited by Homemade on 10 Aug 2013, 19:10, edited 2 times in total.

Post #2 made 8 years ago
Ian - The only true way to know if you need to do a diacetyl rest is to see if it is present/detectable in your sample.
A problem can be if you are capable of detecting it or not, I can't remember ever smelling or tasting butter/popcorn/oily finish in any of my beers. But I don't know whether that is due to it not being present or whether I just cannot detect it?

A simple answer - If you can't detect it in your sample, and it tastes ok to you, then don't worry about it.

There is a lot of information out there (a lot of it anecdotal too), that mentions fermenting cool (lower than 12/13C) reduces diacetyl production. But you may also have to consider the temp at pitching too.

As with all brewing YMMV!
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