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Fermenting Lagers - Couple of q's as its the first one I've done

Discussion in 'General Brewing Techniques' started by jollster101, 8/7/19.

 

  1. jollster101

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    Posted 8/7/19
    Hi all

    I am fermenting my first ever lager which is a NZ Pilsner Fresh Wort Kit in a fermentasaurus using 2 sachets of Saflager S-23 yeast which was recommended by the LHBS (both sachets were rehydrated before pitching again as per the advice from the guy at the shop).

    I was advised to ferment at around 12C and so the night before I set the STC-1000 to 12C and popped the cube into the fridge to come down to the relevant temp ahead of pitching the following day. Standard sanitisation process followed and pitched yesterday morning and set the temp controller to 12C.

    Its been 24 hours and as of this morning there was no activity and the SG remained at 1.046 (via a Tilt hydrometer). Compared to ales (which I have done 5 of with good results), do lager yeasts generally take a bit more time to get going because the temp is a bit colder? I'm not overly concerned but just wondered given this is the first one I've done.

    Another q I have relates to the diacetyl rest. The HBS reps advice was that when the SG gets down to about 1.020, raise the temp to about 17C and then leave for about another week before cold crashing. I was a bit surprised to only raise to 17C as reading John Palmer's book his advice was that you typically upped the temp by 8-12C for a lager. Is the amount you would raise the temp by dependant on the yeast being used?

    When raising the temp for a diacetyl rest can I just set the STC-1000 to the required temp and allow it to come up within a 12 hours or so or is it better to increase by say a couple of degrees a day?

    Any advise from the seasoned brewers on lagers would be great.

    Thanks
     
  2. razz

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    Posted 9/7/19
    Hi Jollster. I think you yeast will get going soon enough, if there is no activity after 48 hours then you most likely have a problem. I take it the yeast was with in date and not old packets? I pitch mine dry and don't bother to rehydrate at all, I'm not sure that will make any difference with yours being rehydrated. It's not so much lager yeast taking longer but that the ferment is at a much lower temp, so will take longer overall compared to ale fermentations.
    D rest is generally done when the yeast has reached 75% of expected attenuation, so approx 1.019-20 will be a good reading to start at. If I ferment at 12 degrees then I raise it to 14-15 degrees in a day or so. The reality is that because the yeast is well and truly motoring at that point you will find that when you get to the D rest temp it will have finished fermenting anyway. I leave it at the rest temp for a couple of days and then start to chill for clearing and transfer to keg. Have fun.
     
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  3. jollster101

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    Posted 9/7/19
    Thanks Razz.

    The ferment kicked off around 24 hours after pitching and is currently down to 1.035. Right now as I type this it is 60 hours since pitching.

    So would it make any difference to raise the temp to say 14C now and then leave it for another day or so until it hits 1.020? I am not sure exactly what happens when it comes to flavours (yet) when yeast are at one temp over another.....still trying to get that understanding.

    It can get a bit confusing with the LHBS rep giving his advice to ferment at 12C until 1.020 and then raise to 17C and leave for a DR before crashing.

    Appreciate the response and advice.
     
  4. razz

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    Posted 9/7/19
    It’s taken 60 hours to drop 10 points, so no, leave it at 12 degrees. You have a good plan, stick to the plan.
    I said 14-15 degrees, the guy at the shop said 17 degrees, not much difference really. Don’t sweat the small things like that.
     
  5. jollster101

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    Posted 10/7/19
    Ok cool, I will leave it as is.

    In your earlier post you mentioned the following.......D rest is generally done when the yeast has reached 75% of expected attenuation, so approx 1.019-20 will be a good reading to start at.

    Is there a simple, idiots guide to how that gets worked out? Do all beers eventually settle out at about 1.010 when the yeast has done its job? Is the main difference where the SG starts at and therefore giving a higher or lower ABV beer?
     
  6. razz

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    Posted 10/7/19
    You need to know the expected degree of attenuation for the yeast you are using. Your S23 I think is approx 73% and your SG is 1.046 so you would expect it to drop 36 gravity points and finish at 1.010. Not all beers will finish at 1.010, it will depend on SG and apparent attenuation.
     
  7. jollster101

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    Posted 13/7/19 at 1:38 AM
    How do you know that it would expect to drop by 36 points? Is there a calculation that can be used with the SG and yeast attenuation?
     
  8. razz

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    Posted 13/7/19 at 3:32 AM
    The attenuation is the yeasts ability to digest the sugars in the wort. If you look at your starting gravity as 46 gravity points and multiply that by the expected fermentation for that particular yeast. I said I thought S23 was 73% attenuation, so a 73% drop in gravity from 1.046 would leave you with 1.012.
    I've just checked the Fermentis website and they say 82% for the S23 which would leave you with a final gravity of 1.009. Sorry for the error.
    https://fermentis.com/en/fermentation-solutions/you-create-beer/saflager-s-23/
     
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  9. MHB

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    Posted 13/7/19 at 5:22 AM
    Apparent attenuation is not an exact science. Its measured in a fully fermentable "sugar" (IIRC glucose) with nutrients. Doesn't mean a wort will react the same, we can change the fermentability by adjusting mash temperature, yeast counts play a role as does wort Oxygenation...
    Pretty useful as a guide but don't be surprised if you don't get the exact number on the yeast. Some makers don't say nothing, some just quote Low-Medium-High.
    Given all that if you want a dryer beer choose a higher attenuating yeast, conversely low for a sweeter beer.

    Generally Low attenuators tend to fall out easily, High attenuators tend to hang around, so if a yeast has High Flocculation it will probably have Low attenuation and the reverse for Low Flocculation.
    Naturally there are exceptions (anything Belgian might break all the rules) one of the things I like about S-04 is that it attenuates fairly well and flocks well to, quick clean ferment, drops pretty bright - works for me.
    Mark
     
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  10. jollster101

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    Posted 15/7/19 at 11:25 AM
    Cool, thanks razz and Mark. That explains things somewhat better for me.
     
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