Yeast Overpitch/Underpitch Experiment From a Microbiologist

CornyKegs 728
Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
BBL_Brewer said:
I'm wondering how you are going to take all those gravity readings with only .5 gal of beer to work with. Are you goind to keep dumping it back in? If so, contamination could easily throw off your results. Plus, getting up in the middle of the night to take 8 gravity readings is not on my list of things to do.
Click to expand...

I use a refractometer and take 100 uls samples... :rockin:

Also, having a 4 month waking up every 2 hours gives me an excuse to do something!
 
Hi All,

So the class that I'm teaching is tomorrow and I decided to blind taste the samples myself. My wife blinded them for me.

I failed to pick out the control versus over or under pitch. However, I could tell a difference between over and under. We'll see how the class does tomorrow!!

Jason
 
Also, having a 4 month old waking up every 2 hours gives me an excuse to do something!

Nice multitasking! Eagerly awaiting the results.
 
just got back from the class! i want to give a huge thanks to brooklyn homebrew and jason the microbiologist for his very informative class.

the beginning of the class talked about the physical aspects of yeast cells and how they metabolize sugar into c02 and alcohol. he also brought slides of different types of yeast and we got to see them under a microscope. got to see 1056 budding and some brett, which is really long and rod shaped, unlike the spherical 1056. that part was cool.

he taught us a cool thing about how to check for diacetyl. you need two class, a cold water bath and a hot water bath, a thermo and some aluminum foil. pour some wort (fermented but before bottling) into the glasses and put one into the hot water and one into cold, covering with foil. let sit for 20min. then take the hot sample and put it into the cold water, you want to make them the same temp. take off the foil and smell. the cold is your control, if the hot sample smells buttery, you need more time on the yeast.

he really stressed temp control and aeration. temp differences of 3 degrees in the first few days of fermentation can really change the flavor, so if you don't have temp control, get it!

another interesting thing was mixing yeasts. start off fermentation with one yeast strain and when you get about halfway through, pitch your second strain and you will get something from both, whether it's super attenuation or a flavor. if it's a low gravity brew, just pitch them at the same time. i'm thinking about mixing saison and english yeast for some kind of mutant high attenuating pepper fruit beast.

last thing was the proper way to step up a starter. don't just cold crash and pitch fresh wort onto the starter cake. you get yeast growth from small beginning numbers of yeast so pull 100ml of starter wort and pitch that into the fresh starter wort, cold crashing the first starter and mixing them when done, you'll get vastly more yeast.

i picked out the overpitch brew but mixed up the under and the control. overpitch was very thin, under was bubblegummy and the control was more fruity. i was just glad to get one haha.

thanks again to everyone there. jason if you're reading this, i was the guy up front with the joker hat :D
 
So for a starter are you saying make a 1L starter and take 100mL from the 1L and add that to the 2L and dump the rest?
 
wegz15 said:
So for a starter are you saying make a 1L starter and take 100mL from the 1L and add that to the 2L and dump the rest?
Click to expand...

he said to take 100ml from the first starter and use that to start your second starter. cold crash the rest of the first starter like normal. when the second starter is done, you'll have much more yeast than if you just pitched new wort onto the first starter cake.
 
that 100ml number comes from the assumption that you're making a 1L starter. if you're doing a 2L starter, make it 200ml, he said that you step in up series of 10. so like if i had a 20ml sample, start it in a 200ml starter, than step it to 2L.
 
MrManifesto said:
that 100ml number comes from the assumption that you're making a 1L starter. if you're doing a 2L starter, make it 200ml, he said that you step in up series of 10. so like if i had a 20ml sample, start it in a 200ml starter, than step it to 2L.
Click to expand...

Thank you for that. The description was a little muddled.
 
MrManifesto said:
just got back from the class! i want to give a huge thanks to brooklyn homebrew and jason the microbiologist for his very informative class.

the beginning of the class talked about the physical aspects of yeast cells and how they metabolize sugar into c02 and alcohol. he also brought slides of different types of yeast and we got to see them under a microscope. got to see 1056 budding and some brett, which is really long and rod shaped, unlike the spherical 1056. that part was cool.

he taught us a cool thing about how to check for diacetyl. you need two class, a cold water bath and a hot water bath, a thermo and some aluminum foil. pour some wort (fermented but before bottling) into the glasses and put one into the hot water and one into cold, covering with foil. let sit for 20min. then take the hot sample and put it into the cold water, you want to make them the same temp. take off the foil and smell. the cold is your control, if the hot sample smells buttery, you need more time on the yeast.

he really stressed temp control and aeration. temp differences of 3 degrees in the first few days of fermentation can really change the flavor, so if you don't have temp control, get it!

another interesting thing was mixing yeasts. start off fermentation with one yeast strain and when you get about halfway through, pitch your second strain and you will get something from both, whether it's super attenuation or a flavor. if it's a low gravity brew, just pitch them at the same time. i'm thinking about mixing saison and english yeast for some kind of mutant high attenuating pepper fruit beast.

last thing was the proper way to step up a starter. don't just cold crash and pitch fresh wort onto the starter cake. you get yeast growth from small beginning numbers of yeast so pull 100ml of starter wort and pitch that into the fresh starter wort, cold crashing the first starter and mixing them when done, you'll get vastly more yeast.

i picked out the overpitch brew but mixed up the under and the control. overpitch was very thin, under was bubblegummy and the control was more fruity. i was just glad to get one haha.

thanks again to everyone there. jason if you're reading this, i was the guy up front with the joker hat :D
Click to expand...


Hi Everyone!

The class was great and much fun! Brooklyn Homebrew is a great LHBS and I will be teaching again sometime in February. I will also repeat this experiment because it didn't turn out as well as I expected it to.

First off, some posters and the beginning of this thread mentioned that my lack of oxygen could be a problem. I think that they were right. Another issue: in my blog you see that the fermenting vessels are clear and not covered. I forgot to cover them for about three days of fermentation. The result: light struck. :(

The beers themselves were not great. This includes the control. The control pitch had a strange phenolic bitterness and smelled skunky. However, having said that, there was a difference between the over and under, but subtle. The over-pitch beer was very clean but bland. The under-pitched beer was fruiter but in an unexpected way. Needless to say, most people picked the control to be either the over or under.

Also, the class was unfortunately rushed since I presented a lot of material. The tastings went quickly, and some people did not score on the polling sheets.

I'm glad I presented this time, and the next occasion will be smoother with less material. Whatever experiment I choose the next time I teach the class the students can reflect on it a bit more. I talked alot about esters and fusels and how to control them during brewing, but I'm going to cut back on it and show more "wet lab" stuff so to speak.

I will post the fermentation data on the pitching rate experiment soon on my blog and will post back. Also, I plan on repeating this experiment with a more expressive yeast and will use oxygen. I was thinking maybe a fruity english strain or a hefeweizen yeast. The next time I present will be in Feb. so I will start the experiment next month ;)

As for stepping the starter...

The ideal dilution step for maximum growth in my hands is 1:10. I use a stir bar and stir plate as this is the only way to get maximal yeast growth.

The example I gave in class, and what I routinely do for lagers:

Target: 400 billion yeast cells (I just did this for a bock I'm brewing next week).

1) 1 liter starter - 1.040 + 1 wyeast smack pack
2) grow for 24, no more. This is key. After 24 hours the yeast will still start to go dormant, building up glycogen reserves. Starters should be "split" when the yeast cells are actively replicating. You should go from 100 billion cells to about 180 billion
3) Dilute 1:10 into a new starter and grow for 24 hours. That means 100 mls into another 1 liter starter. This starter will go from 18 billion to another 100 billion.
4) Cold crash the first starter, decant wort.

At this point you have close to 300 billion, but you need more.

6) Do a third starter from the second as in step number 3, grow for 24 hours.
7) Combine starter #2 into #1, cold crash and decant.
8) After the third starter finishes, you should have close to 400 billion. You can then combine all the starters and pitch into beer.

Keep in mind, this only works with a stirred starter. I believe intermittent oxygenation is not good enough, but rather the gas exchange with a stirred starter provides all the O2 for the yeast to grow. You may need multiple flasks, but not necessarily. You can always have another sanitized vessel on hand to collect the starters.

If anyone has any questions, please post em. I'll answer the best I can.

Cheers and happy brewing!!

J
 
the class was very good. my favorite part was the second bit. learning how the yeast actually process and convert sugars was very cool but in my day to day brewing, i don't know how much of a difference it will make, as i'm not to a level where i can control my mash to produce precise levels of certain sugars. the management of off flavors and yeast plating was the best part for me.

also, sorry if it seems i'm stepping on your toes with this thread. i'm just stoked to talk about the new stuff i learned. :mug:
 
MrManifesto said:
also, sorry if it seems i'm stepping on your toes with this thread. i'm just stoked to talk about the new stuff i learned. :mug:
Click to expand...

Dude no worries!! You had some great questions and yes I agree with what you said. Next time I'll demonstrate more practical stuff. I was pressed for time and felt rushed towards the end.

BTW, you should be getting the powerppint file soon from BK homebrew.

J
 
phattysbox said:
Dude no worries!! You had some great questions and yes I agree with what you said. Next time I'll demonstrate more practical stuff. I was pressed for time and felt rushed towards the end.

BTW, you should be getting the powerppint file soon from BK homebrew.

J
Click to expand...

Could this be shared with all of us nonpaying students?
 
phattysbox said:
Dude no worries!! You had some great questions and yes I agree with what you said. Next time I'll demonstrate more practical stuff. I was pressed for time and felt rushed towards the end.

BTW, you should be getting the powerppint file soon from BK homebrew.

J
Click to expand...

got it, just looking at it now. good stuff.
 
logdrum said:
The 100ml used for the second starter is non-crashed slurry, correct?
Click to expand...

Correct.

However, if the starter is cold crashed and decanted then 1/10 of that volume should be used to inoculate the next starter. If that turns out be 140 mls then one would shake the decanted starter to get the flocs to break up and take 14 mls...
 
phattysbox said:
Correct.

However, if the starter is cold crashed and decanted then 1/10 of that volume should be used to inoculate the next starter. If that turns out be 140 mls then one would shake the decanted starter to get the flocs to break up and take 14 mls...
Click to expand...

Got it, thanks. That makes sense. How anal retentive do we need to be about sanitation/sterilization? If I'm using clean, "star-sanned" glassware, is this going to lead to mutation?

-d
 
logdrum said:
Got it, thanks. That makes sense. How anal retentive do we need to be about sanitation/sterilization? If I'm using clean, "star-sanned" glassware, is this going to lead to mutation?

-d
Click to expand...

Contamination will not lead to mutation, only bad beer... ;) Only stressful situations such as no O2 at beginning of fermentation or really high fermentation temps will cause mutations over time.

As for sanitizing, yes you should sanitize make everything clean as possible. Sterilization is best, but you either need a pressure cooker or autoclave for that.

Treat the starter as if it were a beer (for sanitation purposes)

J
 
phattysbox said:
Contamination will not lead to mutation, only bad beer... ;) Only stressful situations such as no O2 at beginning of fermentation or really high fermentation temps will cause mutations over time.

As for sanitizing, yes you should sanitize make everything clean as possible. Sterilization is best, but you either need a pressure cooker or autoclave for that.

Treat the starter as if it were a beer (for sanitation purposes)

J
Click to expand...

Wow, great info, thanks a ton for taking the time to do this & follow up!

-d
 
A couple questions, since I find this topic interresting:

1. A stir bar will certainly keep the yeast in suspension and delay flocculation, but how does it force oxygen into suspension, to be available to the yeast? I had been led to believe the stir bar speed should be adjusted to make a dimple, not a vortex.

2. If you are repeating the experiment with oxygenation, how are you planning to meter the amount of oxygen in suspension? Certainly as a casual brewer, i just shake the P*&^ out of the fermenter after pitching, but as a lab experiment I assume you want eliminate differing oxygenation levels in the starter as a variable.
 
william_shakes_beer said:
A couple questions, since I find this topic interresting:

1. A stir bar will certainly keep the yeast in suspension and delay flocculation, but how does it force oxygen into suspension, to be available to the yeast? I had been led to believe the stir bar speed should be adjusted to make a dimple, not a vortex.

2. If you are repeating the experiment with oxygenation, how are you planning to meter the amount of oxygen in suspension? Certainly as a casual brewer, i just shake the P*&^ out of the fermenter after pitching, but as a lab experiment I assume you want eliminate differing oxygenation levels in the starter as a variable.
Click to expand...

1. The surface area of a moving liquid under constant stirring is huge and gas exchange occurs at a very fast rate. No O2 is needed and tightly covered foil is sufficient. Either a dimple or a vortex - doesn't really matter. A vortex only increases gas exchange at a insignificant marginal rate more than a dimple.

2. A good question. I would have to get a oxygen regulator to monitor my flow rate. Since I don't have one, and funds are not available for one, I'll have to do my best with the oxygen system I have. I'll make sure to keep all samples the same - i.e. same amount of O2.

I think another important variable here is yeast selection. 1056 is not expressive at all and I might see better differences with a characterful english ale yeast.
 
phattysbox said:
1. The surface area of a moving liquid under constant stirring is huge and gas exchange occurs at a very fast rate. No O2 is needed and tightly covered foil is sufficient. Either a dimple or a vortex - doesn't really matter. A vortex only increases gas exchange at a insignificant marginal rate more than a dimple.

2. A good question. I would have to get a oxygen regulator to monitor my flow rate. Since I don't have one, and funds are not available for one, I'll have to do my best with the oxygen system I have. I'll make sure to keep all samples the same - i.e. same amount of O2.

I think another important variable here is yeast selection. 1056 is not expressive at all and I might see better differences with a characterful english ale yeast.
Click to expand...

I have Williams Brewing oxygen aeration system but no oxygen tank (my local HD was out). If you want I can bring my oxygen regulator + wand + aeration stone next time you will do your experiment.

Where in Brooklyn are you? Tried to send you a PM but your mailbox is full.
 
phattysbox said:
1. The surface area of a moving liquid under constant stirring is huge and gas exchange occurs at a very fast rate. No O2 is needed and tightly covered foil is sufficient. Either a dimple or a vortex - doesn't really matter. A vortex only increases gas exchange at a insignificant marginal rate more than a dimple. QUOTE]

OK, I had assumed ( incorrectly, perhaps) that the pre pitch shaking had to be vigorous enough to force the air "into suspension" mechanically. From what you have said, a gentle swirling with a sanitized spoon for the same amount of time as the vigorous shaking would suffice. Have I missed something? Any idea what the effect of liquid temperature is on the o2 absorption rate? For instance, does o2 absorb faster in a warmer liquid?
Click to expand...
 

Similar threads

dmaxweb
Repitching Yeast Cell Count
Replies
5
Views
573
rizziot
R
Kristoffer84
S04 (and others) When is it overpitch with negative consequences?
Replies
12
Views
2K
hotbeer
hotbeer
O
Do I have an infection? Lager Yeast Fermented Warm
Replies
17
Views
2K
rtstrider
rtstrider
B
Danger of overpitching saved yeast?
Replies
1
Views
703
brewbama
brewbama
Climb
Seeking advice on Brettanomyces
Replies
5
Views
666
Climb
Climb
Yakima 300

Latest posts

Back
Top