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High FG on the last 2 batches of IPA?? 3.8 Plato - should be 2.4 or so

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  • High FG on the last 2 batches of IPA?? 3.8 Plato - should be 2.4 or so

    Hey everyone. I had a problem with the finishing gravities of my last 2 batches of IPA and hoping someone may have a theory as to why.

    Background info - They are batch #9 and #10 of this IPA recipe at the brewery in Costa Rica I'm consulting at right now. I haven't been here too long so still figuring a few things out but this one has me stumped. I've brewed about total 40 batches here in the last 5 months with no real issues, just the usual stuff unitl now.

    5bbl brewhouse/batches

    2 Row Pale 92%
    CaraPils 6%
    Acid Malt 2%

    Mash temp 149-150

    RO water, rebuilt in to mimic typical IPA profile

    Yeast - Batch #9 New pitch 500g Safale 05 (no rehydration), Batch #10 Cone to cone transfer 5th Gen. Safale 05, 6 liters of good slurry (no microscope here)

    Fermentation temp 20C (68F)

    Absolutely nothing out of the ordinary on brewdays, all targets hit

    So here's the problem - Both batches looked typical for first 2-3 days of fermentation and since these FVs don't have sample ports and I have to use the racking arm for zwickel, I tend not to pull samples everyday. By day 4 I start checking gravity and #9 is only at 6 plato. Day 5 5.7P - Day 6 5.6P - Day 7 5.5P, Day 8 5.5P.

    At this point batch #10 is on it's day 2 of fermentation and chugging right along so I pump over about 50liters of krausen hoping to get #9 moving. It doesn't seem to help much and batch #9 just trickles along down to 3.8 plato over 12 days.

    Meanwhile batch #10 follows almost the same pattern, slowing down around day 6 and stops about 4 days later also at exactly 3.8 plato.

    Remember, these are 2 completely different yeast pitches

    Now I've made a variation of this recipe for years at a few different breweries and without fail I get to between 2.2 -2.5 plato in 4-6 days. The past 8 batches of IPA at this brewery have been extremely consistent and without problems. If it had happened on 1 batch I'd chalk it up to yeast health or human error during brewday or poor record keeping or something. But to have both batches act identical just has me baffled. Thankfully they taste OK, not great, a little on the sweet side but not extremely cloying so we should be able to salvage both batches and sell them if we ever get to open again! But for now I just left scratching my head.

    I've calibrated my mash tun probe, used 3 different hydrometers to check samples. No idea?!?!

    Anyone got hunch as to what happened here? Malt health? No "beta enzyme"? I dunno?

    Thanks, stay safe, cheers.


  • #2
    Have you confirmed temp in the FV is actually 68F? Could try bringing them up to 72F to see if they finish out.

    Comment


    • #3
      You have not mentioned wort aeration. You don't need to aerate with fresh dried yeast, but if you are re-using, you will need to do so. If you are aerating, then you might not be adding enough. Also, most big brewers only use the yeast 5 or 6 times before using a fresh culture. So even if you are aerating it might simply be mutating / getting tired and not working as well. Finally, are you adding yeast nutrient - typical around 0.15 to 0.2 ppm zinc as zinc sulphate or zinc chloride.?
      dick

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      • #4
        Dick has great points on aeration and zinc. I tend to prefer zinc heptahydrate and sterile air (as opposed to oxygen).

        My experience having technically supported many US breweries from a large yeast company is 8-10 generations is about average from harvested liquid yeasts. The very refined operations are going about 12-15 generations. Those using dry yeast are more in the 5-6 generation range, presumably because dry tends to be cheaper and allows for more
        economical usage. This (5-6) also tends to be the range for those with in-house propagations. There is no magic number that is “correct”. I have met a few who just “ride the evolutionary rollercoaster” for as many as 100 generations (absolutely NOT recommended). You need to monitor for cell health, counts, flavor profile, total attenuation, and more general details to set your perimeters.

        As far as the issue at hand, you need to pull samples of each troubled beer and run a bench scale ferment on them. Basically Re-dose them with a heavy pitch of new dry or highly active healthy yeast from a known good fermentation. Re-aerate or stir plate if possible. If you experience the same stall or no additional activity, this points to an issue with your wort and not the yeast (probably failure to convert). If fermentation completes, you can look towards the yeast (Temp, pitch rate, viability). Amlyoglucosidase could potentially help if it is a wort based issue.

        Report back and we can suggest further actions.

        Comment


        • #5
          Originally posted by Weehe View Post
          Have you confirmed temp in the FV is actually 68F? Could try bringing them up to 72F to see if they finish out.
          Thanks for the suggestion, I'll do that as soon as the FV's are empty and can pull the probe, but my gut tells me that's not the issue as both batches are in different FVs and no other chilling problems have been seen.

          Comment


          • #6
            Originally posted by dick murton View Post
            You have not mentioned wort aeration. You don't need to aerate with fresh dried yeast, but if you are re-using, you will need to do so. If you are aerating, then you might not be adding enough. Also, most big brewers only use the yeast 5 or 6 times before using a fresh culture. So even if you are aerating it might simply be mutating / getting tired and not working as well. Finally, are you adding yeast nutrient - typical around 0.15 to 0.2 ppm zinc as zinc sulphate or zinc chloride.?
            Thanks Dick

            Yes, aerate repitch yeast at 1.5 LPM to achieve around 6-8ppm, but don't have a DO meter so...….?

            I do not aerate new dry pitch

            Typically run the yeast out 5-6 generations depending on schedule and prior fermentation performance

            No zinc or yeast nutrient. I've been thinking of getting some soon, this should be my "kick in the butt"

            Comment


            • #7
              Originally posted by UnFermentable View Post
              you need to pull samples of each troubled beer and run a bench scale ferment on them. Basically Re-dose them with a heavy pitch of new dry or highly active healthy yeast from a known good fermentation. Re-aerate or stir plate if possible.
              Thanks Unfermentable, basically do a forced fermentation test with a new batch of yeast.

              Both batches have been dry hopped, dosed with Biofine and carbonated at this point. Batch #9 will be packaged today actually. Do you see any harm in pulling a sterile sample at this point and doing the forced ferm test?

              Not really sure when I'll have yeast again since I'm not brewing due to corona virus closure. I might have some 7 gram packets laying around that I could use, I'll look today.

              My malt has been stored at ambient temperature, around 95F during the day, for a couple of months. Could this affect extraction rate? All other gravity samples looked typical, mash sample, preboil, post boil, and OG and ph all looked typical.

              Comment


              • #8
                Simply aerating at a specified rate doesn't mean anything unfortunately - and this comment is not aimed at you specifically, but to all those here who have simply stated in requests for assistance / practices on an aeration rate. Not all the oxygen in that air will dissolve, in fact most of it won't, the amount that dissolves depending on the wort temperature, pressure of the gas, (and thus, crudely, the mass of air being injected), the wort pressure, the size of the gas bubbles once injected, the contact time of those bubbles with the wort, and how long you aerate for, again, affecting the mass of gas injected and available dissolve.

                As unfermentable says about using air, most people (i.e. the yeast strain being used) can get away with using air and achieving saturation - around 8 ppm, depending on temperature and to a lesser extent, wort gravity. But it is difficult, (though not impossible) to achieve higher levels than this when high gravity brewing, or for oxygen hungry yeasts. Using those yeasts though, unless you are brewing high gravity IPA (you don't mention the OG) air should be fine when re-pitching.
                dick

                Comment


                • #9
                  One of the advantages of using air is that you cannot easily achieve over 10ppm of dissolved oxygen in the wort. Bitburger achieves 14ppm or higher with air using a Venturi system, however this is uncommon and is for high gravity wort.

                  Why’s is this 10ppm shelf an advantage? Because yeast does not need over 10ppm of dissolved oxygen at any given time. In fact, once you get above 30ppm you begin to approach toxicity for the yeast. Sterile air allows for less chance of over-aerating.

                  Dick is correct that sometimes yeast requires more oxygen (generally due to more needed cell division on higher gravity beers, but also to influence desired flavor profiles). Oxygen does not want to remain dissolved in wort and will dissipate rather quickly.

                  For this reason, it is advisable to aerate high gravity wort multiple times throughout the initial 24 hours following inoculation (to maintain 8-10ppm DO). This will allow the greatest logarithmic growth and cell health to carry fermentation. Stop aeration well before 48 hours as you want all oxygen to be consumed or scrubbed by the end of fermentation.

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