Liquid yeast pitch rates

[Keruso]

I’m a bit frustrated with liquid yeast. I have recently started to use it, brew number four in the fermenter. All fermentations have struggled, Last brew using WLP051 finished too high at 1.020 I took hydrometer readings on days 11 to 14, it stayed at 1.020 so I kegged it, it wasn’t too sweet but I would prefer if it had dropped lower. Current brew using Omega DIPA yeast is at 1.030 after 12 days and no airlock activity at all. I followed the forum stuck fermentation guide and it’s picked up a bit. I think I’m under pitching. There are a few online pitching calculators which generally agree I need 300 billion cells for 22 litres of 1.075 wort. However there’s dramatically different recommendations for how big a starter is required. Brewunited suggest a 2 litre starter, as does brewersfriend, but on brewuk using the C.White stir plate method, a 2 litre starter is way under what’s needed, only 66% of the necessary yeast, a two stage 3litre starter is needed. This does seem to reflect the problem I’m having, I don’t think a 2 litre starter is enough, irrespective of what some calculators say. I’m going to try a two stage 3 litre starter next time. For comparison I’ve done about 80 brews using dry yeast, two packets each time, not a single stuck fermentation, all hit or exceeded expected FG, all finished in less that 2 weeks. So my instinct is to be conservative and possibly even over build with a 3 litre starter, I just don’t think I’m adding enough yeast. Any advice or experience appreciated.

 

[Brewnaldo]

I would say that the generic, 1 litre 1.040 starter I have treated all of my liquid yeasts to before pitching has ripped through the wort on every occasion except one that finished high, but I suspect poor brewing was to blame for that and not the yeast. I'm no expert on pitch rates by a long way, but as far as effective attenuation goes, I havent had a problem.

That said, 1.065 has been my highest OG so far.

 

[trueblue]

I've used liquid yeast for over 25 years and never had a stuck fermentation. Reading your post I would ask what is your starter regime and what temperature are you fermenting at in comparison to the makers recommendation to start with. Must admit I have not used your strains and have never used an online calculator.

 

[Hanglow]

Are you adding lots of O2 at pitching? You would need to I think to properly ferment a 1.075 beer with most liquid yeasts. Also how are you making your starter? If you pitch a 2l starter at high krausen into a well oxygenated wort it should do fine.

If you don't have O2 one option you could try is to use a yeast that has very low O2 requirements, like chico/wlp001/US05.


Most ales should be at FG in well under a week. I package my ales at 7 days at most now, sometimes less if I can.

 

[Keruso]

Thanks all for your replies, I make the starter following the instructions, clean and sanitize the flask and the stir bar, boil the DME for 10 mins, 200g for a 2 litre starter. Let the yeast pack slowly reach room temperature, sanitize and then pitch, cover the top with sanitized foil, place on the stir plate in the dark for 18-24 hours, then in the fridge to keep for a day or two, pour off some of the liquid, careful not to disturb the settled yeast, on brew day let in slowly come back to pitching temperature and pitch after a thorough mix with a paddle attached to a drill. Then ferment at the suggested temperature inside a STC1000 controlled brew fridge. The yeast is 2 months old so I guess the viable count is around 50%, it has been kept in a fridge. My instinct is there’s not enough yeast using a 2 Litre starter.

 

[peebee]

I ran that starter through a calculator I use ("Homebrew Dad") and it appeared barely enough, based on a very freshly packed (this month) yeast pack and a "standard" ale pitch rate (lager and some continental-type ales will want more). An older pack of yeast and things might struggle.

It's that SG of 1.075 that's the issue. That's pretty strong and will need a lot of yeast to make it work. Consider a two step starter. The calculator was working for me with a six week old pack using 0.7litre first day, 1.2 litre second day (standard 100g DME per litre, SG 1.037). Maybe try sterile cotton-wool to plug the starter flask instead of foil? Many people think a "stirrer" is to keep the starter mixed: That is only part of the story, it's to ensure good gas exchange (CO2 out, oxygen in). 2 litres in a 2 litre flask is cramped. A bigger flask (don't drop it!)? Split between two flasks (needs two stirrers!)? Chill first step, decant, allow to warm, add second step starter (what a faff). A starter is to grow cells: To increase in number, cells must have oxygen.

If the starter is prepared right aerating the wort becomes less of a concern because the calculator has tried to calculate the optimum number of cells to be grown in the starter before pitching. But that's not to say the calculators do much more than roughly guess, so I wouldn't try not aerating, especially in a 1.075 wort.

 

[Braufather]

You could maybe do a lower gravity brew and then pitch onto the yeast cake. You’d defo have enough then.

 

[foxbat]

18-24 hours may not be enough. Go by the yeast not the clock. When it's done all surface bubbles and krausen will have gone and you'll just have a flat looking creamy liquid whirling around.

All of mine get at least 48 hours, sometimes 72 at 20C. It depends on the how the yeast behave and I've never had anything close to a stuck fermentation.

 

[Keruso]

I ran that starter through a calculator I use ("Homebrew Dad") and it appeared barely enough, based on a very freshly packed (this month) yeast pack and a "standard" ale pitch rate (lager and some continental-type ales will want more). An older pack of yeast and things might struggle.

It's that SG of 1.075 that's the issue. That's pretty strong and will need a lot of yeast to make it work. Consider a two step starter. The calculator was working for me with a six week old pack using 0.7litre first day, 1.2 litre second day (standard 100g DME per litre, SG 1.037). Maybe try sterile cotton-wool to plug the starter flask instead of foil? Many people think a "stirrer" is to keep the starter mixed: That is only part of the story, it's to ensure good gas exchange (CO2 out, oxygen in). 2 litres in a 2 litre flask is cramped. A bigger flask (don't drop it!)? Split between two flasks (needs two stirrers!)? Chill first step, decant, allow to warm, add second step starter (what a faff). A starter is to grow cells: To increase in number, cells must have oxygen.

If the starter is prepared right aerating the wort becomes less of a concern because the calculator has tried to calculate the optimum number of cells to be grown in the starter before pitching. But that's not to say the calculators do much more than roughly guess, so I wouldn't try not aerating, especially in a 1.075 wort.

Thanks, I really do find starters a real faff as well, next brew is 1.067, 55% viability due to yeast age, calculator say I need 270b cells, Using 1 litre step 1, then 2 litre step 2 should give 350b cells, I’m going to try 24 then 36 hours, fingers crossed

 

[Ben034]

I’m a bit frustrated with liquid yeast. I have recently started to use it, brew number four in the fermenter. All fermentations have struggled, Last brew using WLP051 finished too high at 1.020 I took hydrometer readings on days 11 to 14, it stayed at 1.020 so I kegged it, it wasn’t too sweet but I would prefer if it had dropped lower. Current brew using Omega DIPA yeast is at 1.030 after 12 days and no airlock activity at all. I followed the forum stuck fermentation guide and it’s picked up a bit. I think I’m under pitching. There are a few online pitching calculators which generally agree I need 300 billion cells for 22 litres of 1.075 wort. However there’s dramatically different recommendations for how big a starter is required. Brewunited suggest a 2 litre starter, as does brewersfriend, but on brewuk using the C.White stir plate method, a 2 litre starter is way under what’s needed, only 66% of the necessary yeast, a two stage 3litre starter is needed. This does seem to reflect the problem I’m having, I don’t think a 2 litre starter is enough, irrespective of what some calculators say. I’m going to try a two stage 3 litre starter next time. For comparison I’ve done about 80 brews using dry yeast, two packets each time, not a single stuck fermentation, all hit or exceeded expected FG, all finished in less that 2 weeks. So my instinct is to be conservative and possibly even over build with a 3 litre starter, I just don’t think I’m adding enough yeast. Any advice or experience appreciated.

Are you sure that it is stuck and hasn't finished? You said you used WLP051 on a 1.075 wort? If you got to 1.020, this work out at 72% apparent attenuation which is right in the middle of the 70-75% advertised range for this yeast. Have you tried a higher attenuating yeast? Or mashed at a lower temperature?