The Science Behind Blow-Offs & Krausen Size

[Evan!]

Blow-offs and krausen size in general are constantly discussed around here, but I don't think I've ever seen the science behind it really explained. So, those of you who are a little more versed in the world of the biologic, help us out here. Why do some batches blow off or have very large krausen, while others have virtually none? I know some of it has to do with the yeast strain, but why? And why is there variation from one batch to the next with the same strain?

For example, I made a Rochefort 10 clone with the Wyeast Abbey II yeast, fresh from a smack pack with a big starter. It blew off like none other. I then reused that yeast cake for a Stone Vertical Epic clone, fully expecting it to do the same thing again (since yeast cakes have such a high cell count)...but, while the fermentation was vigorous and quick, the krausen never got to be more than 1/2" high. This is with the same yeast.

There seems to be no rhyme or reason behind krausen size. Whenever I'm expecting a blow-off, I don't get one. So, can we get to the meat of the science?

 

[FlyGuy]

I think it has most to do with the recipe. For example, a hefeweizen or wit or oatmeal stout really seem to make a thick, persistent krausen. They have lots of proteins in the mash, which aid in head retention of the beer, but also in 'krausen retention'. That's my guess, anyways -- the factors that lead to good head and head retention are correlated with big krausens (here is a good article on the subject).

 

[RickWG]

Just did a Bavarian Wheat with wyeast 3056 and got my first blowoff. I'd heard that wheats were a bit more vigorous so I've been watching. I also used a blowoff tube. I'm also a scientist so observing is what I do and here's what I noticed....

Upon addition to my carboy from the boil the head was much more pronounced.
The krausen seemed to have much more body to it. Foam, not yeast.
The fermentation activity, while active, wasn't really anymore acitive bubblewise than many others I've seen.

I would think that in this case the large krausen is due to the different properties of the wort and not vigor of the yeast. Proteins, oils, hop oils...etc left in the wort contributed to the retention of the head/krausen and not vigor of yeast.

Case by case basis this is the observation of my "blowoff"

( i guess I was right on with the previous poster just not as quick.)

 

[olllllo]

Case by case basis this is the observation of my "blowoff"

Carboy Scene Investigators.

 

[impatient]

Doesn't really look like this took off very well. I would like to hear more on this subject from those who know??

 

[TheFlatline]

I just had my first blowoff with an irish stout recipe. I'm going to pay attention to the head retention for that batch, to see if there's a correlation.

 

[boxerbrew]

I pitched on a cake recently and rigged a blowoff, as this always is a little hectic and it didn't do anything. I checked about 4 days later by taking the lid off and noticed about 2 inches of krausen so all was well, but I guess nature has it's own agenda and it's own schedule. After all , its like a thunderstorm, sometimes your lawn furniture blows off the deck, and sometimes it doesn't. Nature has it's own ideas.

 

[frolickingmonkey]

I just had my first blowoff with an irish stout recipe. I'm going to pay attention to the head retention for that batch, to see if there's a correlation.

I had my first and only blowoff with a brown porter I brewed about 8 weeks ago, but I wouldn't say that the head retention is equivalent. I'd say it's kind of weak, so in my particular case I don't see a correlation. I'm interested to see the report on your stout, though!

 

[menschmaschine]

This is an interesting topic and probably has a more complex explanation than we'd all like. I'm gonna take a stab at it, but someone like Greg Noonan or George Fix's ghost (may he rest in peace) would probably do best.

-Lager yeasts have a smaller/lower krausen than ale yeasts because they favor anaerobic fermention (ferment closer to the bottom). This leads me to believe that various ale yeast strains require varying degrees of aerobic fermentation... so some strains produce more krausen than others because they ferment closer to the top.

-CO2 production... I'm sure individual yeasts strains produce individual levels of CO2. Those that produce more, have the potential to produce higher krausen.

-Protein composition in the wort will influence krausen formation (more proteins of certain sizes = more krausen.) Possibly other non-sugar compounds in the wort like amino acids, minerals, etc. This could be a big reason... it's why apfelwein has no krausen.

-Specific gravity... higher gravity (more sugars) = more krausen. And possibly, certain types of sugars in higher quantities = more krausen. But along with higher gravity comes more proteins, so maybe it's not the sugars, per se.

-Fermentation temperature... higher fermentation temps = more vigorous fermentation and, therefore, the potential for more krausen.

-Yeast health and viability... happy yeast = more vigorous fermentation = more krausen.

I pulled all that out of my ass, so if it smells like a lager fermentation, that's why.

 

[heinz57]

I pulled all that out of my ass, so if it smells like a lager fermentation, that's why.

What a good quote.

 

[GloHoppa]

Blow-offs and krausen size in general are constantly discussed around here, but I don't think I've ever seen the science behind it really explained. So, those of you who are a little more versed in the world of the biologic, help us out here. Why do some batches blow off or have very large krausen, while others have virtually none? I know some of it has to do with the yeast strain, but why? And why is there variation from one batch to the next with the same strain?

For example, I made a Rochefort 10 clone with the Wyeast Abbey II yeast, fresh from a smack pack with a big starter. It blew off like none other. I then reused that yeast cake for a Stone Vertical Epic clone, fully expecting it to do the same thing again (since yeast cakes have such a high cell count)...but, while the fermentation was vigorous and quick, the krausen never got to be more than 1/2" high. This is with the same yeast.

There seems to be no rhyme or reason behind krausen size. Whenever I'm expecting a blow-off, I don't get one. So, can we get to the meat of the science?

Well could it be that the reason that your Vertical Epic clone didn't explode would be because while the cell count was high, it wasn't as high as you might have thought due to viability? Having had the chance to shadow the brewers at work, they do cell counts to pitch the exact right amount of yeast. They pull a sample and then count the amount of cells with a hemocytometer. They then stain the cells and see how many are still alive. The percentage of viable cells versus the overall count tells them if and how much they should pitch for the batch. With those general principles, its possible that for whatever reason you just didnt have a good viability.

This is me with no science background whatsoever theorizing

 

[Hombru1]

Kind of new here but I would have to say menschmaschine's response is as close as I could get without some real investigation. I am finishing up a MS in microbiology but I have little experience, outside of brewing, with yeasts. I would think the biggest players aside from the strain would be SG (viscosity), and protein levels. When I take a break from my thesis writing I will try to look into it some more.

 

[Champurrado]

I'd just like to know why I found my pantry floor covered in beer foam this morning when I woke up. Never had a blowout before. Airlock was still attached but the foam had burbled out the holes and down the carboy. Replaced airlock with a blowoff hose and it's fermenting mightily.

 

[humann_brewing]

I am currently using WLP002 on a Porter and will recycle it to put a RIS on top of it in a couple of weeks. We will see who blows off the most.

The current one is going to go crazy as it only has a few inches to the top of the carboy as I had a lot more than I expected with my final volume. This is also the first time I have used a blow-off tube as I am sure I will need it.

 

[antsp1]

I am sure it probably has to do with the amount of protein in the wort. It may not be scale directly, and I would assume that lipid production will intensify the foaming mechanics.

Most modern fire fighting foams are protein based, add that to any excess lipids in the mixture, and you have a potential for blowoff.

Ant

 

[FlyGuy]

Although Menschmaschine was a bit off on a couple ideas (I am curious to see if our budding microbiologist will spot them!), I generally agree with his thoughts. Protein concentration, yeast health, and CO2 production are key. Yeast concentration (which largely determines the RATE of CO2 production and krausen formation) and CO2 solubility (affected directly by temperature) are also other critical factors.

I suspect that the big determinants are (1) your recipe, specifically the grainbill (high protein grains and adjuncts are key) and gravity, (2) fermentation conditions, especially temperature, and (3) yeast pitching rates and condition (but not really yeast strain).

 

[maltMonkey]

The only major blow off I've ever had in over 40 batches was a couple weeks ago with a low gravity cream ale, fermenting around 65° with 3 gallons headspace and no starter.

The only thing about this batch that was different from any of the rest was that I used about 15% flaked corn, so I'm chalking it up to that.

 

[menschmaschine]

Although Menschmaschine was a bit off on a couple ideas (I am curious to see if our budding microbiologist will spot them!).

If you don't tell me, how am I going to learn?

Seriously, I have a biology-based science degree, which is why I love the scientific aspects of brewing, but I'm no know-it-all and college was some time ago.

I forgot about the CO2 solubility and temperature relationship... good one!

 

[pjj2ba]

various ale yeast strains require varying degrees of aerobic fermentation...

Let the learning begin! This would make a good wrong answer for a multiple choice question. If I saw this as an answer I could immediately rule it out as it uses two mutually exclusive terms (technically speaking).

We'll see if the budding microbiologist gets this.

Another hint would be an hypothesis of mine that this also relates to which is why underpitching can potentially lead to more yeast derived flavors (often bad), and less alcohol, compared to one pitched at the proper rate and therefore spends less time building up to a good cell density.

 

[Brewsmith]

I'll chime in here. Most of the answers seem to be close, but not entirely complete. I'm going to say it has to do with at least 6 different factors:

Proteins - This is grain bill dependant. The more Wheat, Flaked Barley and other grains high in protein content that you have in the grist, the more is going to end up in the finished beer. These protiens are what contribute to head retention, and big fluffy pillows of foam. During fermentation you have the same activity going on. CO2 bubbles up through the beer, creating the krausen. More protein, more likely for big krausen.

Yeast Strain - Some yeast strains are generally more active than others, while some plod along and you can't rush them. Hefeweizen yeasts, and some English strains are notorious for finishing their job in only a couple days, making the CO2 production faster, pushing more yeast to the top. These fast yeast are also notorious for losing health quickly, while the slower yeast seem to have a longer shelf life. Kinda like James Dean, life fast, die young.

Yeast Flocculation - As yeast ferment they begin to clump together, or flocculate. When they stick together, they form more surface area for CO2 bubbles to carry them to the surface of the beer. As fermentation slows down, the flocs sink faster to the bottom of the vessel. A more powdery yeast should not form as much krausen, but it will also clear slower.

Yeast Health - Heathy yeast is more active than unhealthy yeast. Fresh yeast, making starters, or repitching favors more healthy yeast. Healthy yeast will produce more CO2 faster, hence the bigger krausen.

Temperature - Yeast ferments in the beer, not on top or the bottom, and the whole ale/lager top fermentation/ bottom fermentation thing is a misnomer. Both ales and lagers can form a krausen, and then when both are finished, the yeast settles to the bottom. In a lager, or beers fermented at cooler temperatures, CO2 dissolves easier into solution, so more CO2 is in solution and not coming out the air lock. Also, yeast act more slowly at colder temps, producing less CO2 in a given period of time. This is why lagers can take 48 hours before showing signs of active fermentation, while ales can be done in the same amount of time. For the lager, fermentation may be happening, but the CO2 being produced is staying in solution. Conversly, fermenting warm (over 72 or so) will have those yeast going like gang busters, ripping throught the sugars in no time, again producing CO2 at a rapid rate and creating a big krausen.

Fermentation Vessel Geometry - A taller, narrower fermentation vessel will have less surface area on top than a wider, more shallow fermenter. When all the CO2 is coming out of a much smaller surface area, the resulting krausen will be much taller. Think the Mississippi river compared to a creek. The volume of water flowing on the Mississippi is huge in sheer volume, but the speed is very slow because the river is so wide. In a creek, the speed is high because the channel is so narrow, even though the actual volume of water may be less.

 

[Champurrado]

I'll take Temperature for $100, Alec. Most of my earlier batches were fermented at 68 degrees in a temperature controlled fridge. This is the first batch at "room temperature" of about 71 degrees. I guess that much temperature increase caused my foaming. I also used liquid yeast for the first time (WLP001) instead of nottingham.

 

[babalu87]

I know this.
I think I could put Wyeast 1007 in a bucket of water and get a blow-off

 

[menschmaschine]

This would make a good wrong answer for a multiple choice question. If I saw this as an answer I could immediately rule it out as it uses two mutually exclusive terms (technically speaking).

You're right. I stand corrected. That's why I love science... not a whole lot of room for opinions!

 

[Kaiser]

Brewsmith, nice summary.

Yeast Flocculation - As yeast ferment they begin to clump together, or flocculate. When they stick together, they form more surface area for CO2 bubbles to carry them to the surface of the beer. As fermentation slows down, the flocs sink faster to the bottom of the vessel. A more powdery yeast should not form as much krausen, but it will also clear slower.

I have a comment on that though. Flocculation is something that happens when the yeast runs out of sugars. For flocculating yeasts, the sugars (glucose and maltose) in the wort act as flocculation inhibitors and when they are gone the yeasts will flocculate. The intersting point is that the ale yeasts that were cited to form a very large Kraeusen are also non flocculating yeasts (WY1007, WY3068, basically all German ale and wheat yeasts).

So what makes them float to the top is not so much flocculation but the formation of colonoies which form when the daugther cells don't seperate from the mother cells. In addition to that the cell surface of (at least some) top fermenting yeasts is hydrophobic which promotes the formation of CO2 bubbles on the yeast cells that in turn causes the cells and their colonies to rise.

I started to look into this a little after I had a discussion about this with Jamil Z. He made the general statement that top fermenting yeasts are more flocculant than lager yeasts. While German ale and lager yeasts like WY2206 certainly show the opposite. I wasn't able to convince him that his statement was incorrect. Oh well.

Kai

 

[Brewsmith]

I'm no expert, I was trying to pull all of that out of my head with stuff I've read and heard. It makes sense. I'll I was really trying to say is that yeast is carried by CO2 to the top of the fermenting beer and whether it's flocs, colonies, groups, clumps, posses or whatever, they are more easily taken up to the surface.