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Hello, we have been having problems with our house English ale yeast reaching target attenuation. It is reaching approx 73% attenuation but it is not ideal. We propagate our own yeast in our in house lab every 14 generations or so. The last two propagations have been ideal for the first and second generations as it is reaching approx 80% attenuation but after the second gen it struggles to reach our target attenuation and is just getting to approx 73%. So we have looked at acid washing procedure which we would normally only acid wash from third gen onwards,but the last propagation we didn't acid wash on the third gen and we still had the same problem. The lab does a forcing test on every brew so we know the attenuation limit is ok and mash temps are ok. We also add zinc into the wort at collection and also have an inline oxygen supply. We have changed the oxy rate but hasn't made a lot of difference. Any advice would be greatly appreciated.
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I assume this is a new yeast for you. Just because you are adding oxygen, doesn't mean it is all dissolving. If you are actually using air, and not oxygen, then you can achieve only at best 10 ppm, probably closer to 8 ppm DO2. If using pure oxygen, theoretically you can get closer to 30 ppm. Some yeasts definitely need more oxygen than air can supply. One large Yorkshire brewery used to need about 27 ppm oxygen for their ale yeast (so I was informed on one visit). So you need to know how much you are adding - mass flow or flow meter + known pressure to be able to calculate the O2 addition, fine gas bubble formation at injection (sinter or venture system ideally) turbulent flow, mixers and back pressure to get it all in solution.
If you screw up the acid washing it tends to affect that brew, not just subsequent brews, so as you indicate, I doubt that is the reason. Some yeasts simply do go off very quickly - again one I have worked with was virtually useless at fourth generation. If you are using a mixed yeast, you may be preferentially cropping the low attenuation yeast. Check your storage conditions - 3 deg C for 48 hour max ideally, but of course people do keep yeasts for longer, but lose vitality.dick -
Are you top cropping or bottom cropping? Our only choice is to harvest from the cone and we ran into similar challenges with a couple english strains over the last two years. We saw improvements when we:
1) Harvested earlier
2) Only dropped the beer to 55 - 60°F for harvesting vs 35°F
3) Increased our oxygen additions during knockout
4) Pitched at a full 1 million cells/ml/°P, even for session-strength beers
Even with these changes we still only ran the yeast for 6 generations compared to the 10 - 12 generations we normally go with our American yeast strain. Eventually we landed on a strain that seemed to be more conducive to our brewing, harvesting, and overall production schedule. Your results will most likely vary based upon your particular yeast choice.
Cheers,
TomComment
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thanks for both replies, today I have been looking into the oxygen route. Like I said we have an inline stone and deliver approx 5 litres per minute. We don't have anyway of checking if this is being dissolved or its breaking out. The yeast we use has been long standing in the brewery so not a new addition. I have wondered about cropping times as this is done from the top as we have flat bottomed tanks.Comment
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5 litres / minute at what pressure? And into wort at what flow rate. Simply stating a flow rate is totally meaninglessdickComment
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Hello, flow rate of the wort is approx 125 litres per minute. The system we have hasn't changed and worked well previously but for the last three months like I said in my first post that the yeast is struggling to get to its attenuation. I looked back on brew sheet data today and found some brews was only making 68% attenuation. But this is at rack so some residual sugars do remain for secondary fermentation. Thanks.Comment
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and what is the gas pressure?dickComment
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Also not sure of the pressure on the tank. We use food grade o2 from Boc. The tank is opened and we adjust flow rate on the float for litres per minute.Comment
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Its not the tank pressure - what pressure is the line pressure at the point at which you inject it into the wortdickComment
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Hello, again thanks for bearing with me. I will talk to the engineer tomorrow.Comment
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