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  • Vermont IPA process question (diacetyl, dryhop, yeast harvesting)

    Hi everyone,

    Soon we are getting ccts that can hold up to 2.0bar pressure and therefore I want to naturally carbonate our beers. Please no discussion why I don't want to force carbonate. This would be my last resort so preferable I want to spund at the end of primary fermentation.

    I want to change our strain to vermont ipa and have a question regarding the process I have in mind.

    - ferment at 19-21°C
    - harvest yeast on day 3/4
    - close fv when pg is 1°P (day 5) above fg
    (Now comes the critical point)
    - immediately lower temperature to 15°C and dry hop
    - let beer fully ferment and after fg is reached hold this temp for another 2 days (day 6 and 7)
    - go down to 12°C on day 8 and rouse with CO2
    - go down to 0°C mature for a few more days and keep drawing off yeast and hop slurry
    - transfer to bbt and keg/can

    Now my questions
    - will there be enough yeast to harvest at day 3 (vermont ipa is a low to medium flocculant strain)
    The thing is that if I could not harvest during primary this would make dryhopping more complicated. Let me explain why. I want to spund at the end of fermentation so the beer would be already carbonated which means I cant just throw the hops in after this point (gushing). Therefore I need to dryhop from a pressurized container (keg) and transfer the dissolved hops into the tank. Everything under pressure of course. I also would need to harvest first before dryhopping. So to make a long story short. Will there be enough yeast during primary or will I have to lower the temperature to harvest sufficient amounts with this strain?

    - I have to lower to 15°C after closing the fv not to exceed the 2.0 bar. If I set the spunding device to 1.4bar this gives me 4.6g/l at the top and about 5.2g/l at the bottom (1.7bar due to the hydrostatic pressure of the beer) of the fv. I want to end up with about 4.5-5.0g/l in the keg or can. So this process step is forced upon me due to the pressure limitations of the tank. I would prefer to keep the temp at 19°C but I can't because the pressure would rise to high. My actual question is: If I am at 1.014, close the fv, cool to 15°C and the beer finishes at 1.010 will this be alright regarding diacetyl reduction? Keep in mind that I would hold the 15°C after fg is reached for another 2 days but still....too cold?

    So it comes down to two points
    - enough yeast to harvest during primary?
    - sufficient diacetyl reduction at 15°C at the end of fermentation over three days?

    Thanks in advance for your input and ideas.

    Matthias

  • #2
    Diacetyl reduction is both time and temperature dependent, often times extending well into the stationary phase. But I would be concerned about diacetyl reduction at temperatures any lower than 18-19C.

    YRMV, but cropping between day 3 and day 5 isn't unheard of.

    Comment


    • #3
      Hello,

      it has been a while...I was busy brewing ;-)

      I have not harvested from a batch at day 3. This strain produces delicous beer but it very non flocculant. We dryhop at day 4, spund and let it carbonate. No harvesting from keg batches.
      For cask batches we do harvest after diacetyl rest and cold crashing to 5C.
      Primary 4 days (at 20C), 1day diacetyl rest, 1 day cold crash and harvest on day 7. We fill three corny kegs of quite liquid slurry from a 30hl batch.
      Last cell count from yesterday was 1.32*10^9 cells. To repitch a 30hl batch of 10P strength this would be ok.

      Cells needed = 3000000ml*10*800000cells/ml = 24*10^12cells

      Volume of slurry needed = 24*10^12/1.32*10^9 = 18200ml = 18.2L

      This would be perfect because we harvest about 20L in each keg. However, we experience very low viabilities (about 60%). And this is from a freshly harvested yeast sample. We try to repitch as soon as possible obviously but from time to time we have to keep a keg for about 10 days which makes the viability decrease even more.

      Why do we see so low viabilities? With our session pale (3.8% ABV) fermentation is good but with our APA (4.7% ABV) fermentation slows down towards the end and it might even take 6 days to reach FG. I think this is due to underpitching because of the low viability.

      Btw...no diacetyl problems with this strain whatsoever, neither in cask or in keg.

      Any suggestions would be much appreciated.

      Matthias

      Comment


      • #4
        Aeration - or lack of is the first thing I would look at
        dick

        Comment


        • #5
          Vermont IPA yeast from who? There are more than a few.

          Comment


          • #6
            Originally posted by dick murton View Post
            Aeration - or lack of is the first thing I would look at
            This...Do you use oxygen or air? What rate? Also do you use yeast nutrients? Do you crop the harvest, or just collect all the yeast?

            Personally I would not pitch a yeast with 60% viability no matter what. You are looking at a large probability of autolysis will all the dead cell mass.

            IMHO, you can usually get away with fairly low pitch rates if you are providing enough oxygen to the cells. It has been my experience that over pitching is more inclined to cause early stalls in general. Not enough daughter cells are produced causing a great takeoff, but then no younger cells to carry out fermentation in the stress of more alcohol and lower pH. This can also translate to low viability since the majority of cells present have expelled their energy potential earlier in the process. The younger cells would have higher rates of viability and vitality.

            I would expect to see a low pitch rate due to poor viability have a slow takeoff. If you have the means to cell count, you can also look at the bud scars to see if you are generating a lot of new cells in the process, or if they are limited. That could give you an idea if the above is happening. Each cell may bud up to 20-30 times at peak reproduction, but if you only see a few scars you may not be aerating enough, or possibly over pitching. There is usually a peak cell density reached and the higher pitch rate will cause that to be met before many young daughters are produced.

            One day of crashing before harvest can present problems too. If crashing very quickly yeast can have a hard time storing energy (glycogen) which is vital for prolonged storage periods. In fact, it can be more essential than viability when factoring lengthy storage. In a perfect world you might step down the temperature consistently over a two day period to signal to the yeast a need to store energy before entering dormancy. While it may not directly improve viability, it will have a huge impact on vitality, and therefore the length of time you can store the yeast.

            Comment


            • #7
              Do you mind to share what pitching rates do you aim for when reusing ale yeast?

              Comment


              • #8
                Hi,

                Thats the strain:


                I aerate for the whole knock out (30hl) which takes about 40min with 1.0l/min pure O2

                I aim for 0.8-1.0 mio cells per ml per degree plato.

                Under the microscope I see a lot of blue cells but some of them are budding (are those even dead?). How do you count? I cant get my head around why one day after primary fermentation 40% of all the cells would be dead...

                Matthias

                Comment


                • #9
                  You don't want to count newly budded cells as dead even if they turn blue. There may not be enough metabolism to expel the dye in freshly budded cells. Also you typically don't count an attached bud unless it is at least half the size of the mother cell. Most people use a quick count of the four corners and one center box. Most don't count the cells touching the top line or right side, but do count the bottom and left side.

                  If you are pitching a 60% viable pitch, it would stand to reason you will see 40% dead in your counts. Your initial pitch rates seem within reason. Are your fresh pitches having low viability or is it much higher? Perhaps oxygen is a bit too high, but still seems reasonable to me. A lot of the dissolved content has to due with the stone, temp and length of hose. Oxygen can be toxic to the yeast in high quantities.

                  I'd still suggest a cropping technique where you remove all the early dropped yeast (probably more dead cells, but you can stain and count) then crash for a longer period, then harvest. If you are using a very non flocculant strain it stands to suggest that the healthy cells are still in suspension when you do your harvest. I would take counts/stains of the fermenting beer to watch for cell density changes and viability in the beer throughout the process in addition to the yeast harvest. Then you have an idea if you have healthy yeast in the beer and you just aren't collecting it, or if you are having issues getting healthy yeast to begin with. You could also add yeast nutrients (if you aren't already).

                  The non flocculant strains usually do better with a krausening approach over a crash harvest, in my experience. Especially if you desire cloudiness. 10 days is a long time to store yeast without feeding it sugar and oxygen, especially if harvesting quickly after crash. Try giving a little wort from your other batches when storing for a long time.

                  Comment


                  • #10
                    How do you look at the bud scarring? When I count cells in the hemacytometer, it doesn't seem to be a high enough magnifications (40x lens) to see scarring. Do you look at it with the oil immersion lens? How many bud scars is ideal for a yeast slurry in the higher generations?

                    Thanks!



                    Originally posted by UnFermentable View Post
                    This...Do you use oxygen or air? What rate? Also do you use yeast nutrients? Do you crop the harvest, or just collect all the yeast?

                    Personally I would not pitch a yeast with 60% viability no matter what. You are looking at a large probability of autolysis will all the dead cell mass.

                    IMHO, you can usually get away with fairly low pitch rates if you are providing enough oxygen to the cells. It has been my experience that over pitching is more inclined to cause early stalls in general. Not enough daughter cells are produced causing a great takeoff, but then no younger cells to carry out fermentation in the stress of more alcohol and lower pH. This can also translate to low viability since the majority of cells present have expelled their energy potential earlier in the process. The younger cells would have higher rates of viability and vitality.

                    I would expect to see a low pitch rate due to poor viability have a slow takeoff. If you have the means to cell count, you can also look at the bud scars to see if you are generating a lot of new cells in the process, or if they are limited. That could give you an idea if the above is happening. Each cell may bud up to 20-30 times at peak reproduction, but if you only see a few scars you may not be aerating enough, or possibly over pitching. There is usually a peak cell density reached and the higher pitch rate will cause that to be met before many young daughters are produced.

                    One day of crashing before harvest can present problems too. If crashing very quickly yeast can have a hard time storing energy (glycogen) which is vital for prolonged storage periods. In fact, it can be more essential than viability when factoring lengthy storage. In a perfect world you might step down the temperature consistently over a two day period to signal to the yeast a need to store energy before entering dormancy. While it may not directly improve viability, it will have a huge impact on vitality, and therefore the length of time you can store the yeast.

                    Comment


                    • #11
                      Originally posted by UnFermentable View Post
                      You don't want to count newly budded cells as dead even if they turn blue. There may not be enough metabolism to expel the dye in freshly budded cells. Also you typically don't count an attached bud unless it is at least half the size of the mother cell. Most people use a quick count of the four corners and one center box. Most don't count the cells touching the top line or right side, but do count the bottom and left side.

                      If you are pitching a 60% viable pitch, it would stand to reason you will see 40% dead in your counts. Your initial pitch rates seem within reason. Are your fresh pitches having low viability or is it much higher? Perhaps oxygen is a bit too high, but still seems reasonable to me. A lot of the dissolved content has to due with the stone, temp and length of hose. Oxygen can be toxic to the yeast in high quantities.

                      I'd still suggest a cropping technique where you remove all the early dropped yeast (probably more dead cells, but you can stain and count) then crash for a longer period, then harvest. If you are using a very non flocculant strain it stands to suggest that the healthy cells are still in suspension when you do your harvest. I would take counts/stains of the fermenting beer to watch for cell density changes and viability in the beer throughout the process in addition to the yeast harvest. Then you have an idea if you have healthy yeast in the beer and you just aren't collecting it, or if you are having issues getting healthy yeast to begin with. You could also add yeast nutrients (if you aren't already).

                      The non flocculant strains usually do better with a krausening approach over a crash harvest, in my experience. Especially if you desire cloudiness. 10 days is a long time to store yeast without feeding it sugar and oxygen, especially if harvesting quickly after crash. Try giving a little wort from your other batches when storing for a long time.
                      These are some great tips, thanks for that.

                      Lately Im observing some strange things. Bought two fresh pitches. London Ale and Vermont. Pitched london ale in 26hl and did not finish at all. Stalled at about 1020 (coming from 1040) and slowly went down to 1014. The other pitch (vermont) stalled at 1023 coming from 1038. I aerated the vermont batch with 1.5l/min during the whole 40min knock out because I thought I underaerated the london ale batch. But it still stalled and is creeping down now really slowly. I had another batch which was 5th generation vermont ale and this one stalled at 1030 coming from 1046 but is going down now after I aerated again in the FV.
                      My knock out hose is quite long (10m) but the issue appeared suddenly from one batch to the next. Yesterday I pitched a Porter with the second generation london ale harvested from the 1040 batch. Pitched 40l of thin slurry into 26hl. Ph dropped after 12h and after 24h started bubbling. Lets see if it will stall....I hope not. But I aerated well and pitched a good amount of yeast. A little bit off topic but these are just some observations I made.

                      Matthias

                      Comment

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