Poor efficiency or bad read?

[FatDragon]

The core question first: can AG wort stratify like poorly-mixed extract wort is known to do?

Did an oatmeal porter last night (supposed to be Old Engine Oil Pseudoclone but I didn't have my recipe handy and it was a bit off) and I seem to have gotten rather poor efficiency. I BIAB and normally pull 85-87% mash efficiency, but this time I'm looking at something closer to 62% if my hydro reading was correct.

The recipe:

3kg Pils
.7kg Vienna
.5kg Roasted Barley
.15kg Black Patent
.4kg Unmalted Buckwheat
1kg Flaked Oats (added to the mash whole because of doughball problems last time when I milled them)

60 minutes @ 69C/156F, stirred once after mash-in.

The mash was uneventful, but my draining bucket/pourover sparge took a long, long time and I left the grain wetter than usual because of the viscosity of the oats.

Boil, etc.

Spring has come, and with it warmer ground water. I stopped chilling around 25C because that last few degrees takes a ton of water, so I decided to toss the pail in a fridge for a couple hours instead. A couple hours later it's around 21C and I scoop out a gravity reading off of the top with a sanitized ladle (not my typical procedure but I forgot to get one earlier and didn't do a pre-boil reading either) and sprinkle my S-04 before transferring to the ferm chamber (set to 17C) with a blowoff. I'll admit it was late at this point and I was disheartened to see the hydrometer sitting so low so I didn't look closely enough to see the exact reading, but where I was expecting 22L of wort at somewhere around 16.5p (that's 1.068), I got 23L of wort closer to 11p (1.044).

Now I'll be honest: this was an ill-advised last-minute brewday and I got a number of things wrong, including creating a recipe that was about 10 points higher than I wanted because I was afraid the wort wouldn't have enough diastatic power if I cut the base malt any lower than I did. If this really ends up at 1.044 and gives me a creamy 4-4.5% oatmeal porter, that's A-OK with me. I know that my efficiency probably wasn't 85% like usual because I left more wort in the grains than usual, but did I really lose 25% efficiency on this brew, or was my wort stratified by the time I spooned out the OG sample so I got a tube of diluted wort and I'll just have to measure the ABV with the old "how many before I'm hammered" test?

 

[Cyclman]

If you have a controlled process, I would bet over that time your wort stratified.

 

[FatDragon]

If you have a controlled process, I would bet over that time your wort stratified.

That's generally what I'm hoping. I didn't do anything significantly different from other batches aside from sparging a bit extra to make up for the liquid left in the grain bag, but this is only my second time using such a large percentage of oats in a brew (and first time not milling them to avoid doughballs), so while my process was the same, the results may not be.

 

[brewkinger]

Thermodynamically speaking, ANY fluid will experience thermal stratification as it cools.
Your sample from the top would be less dense than the layers below it.

 

[Qhrumphf]

Now I'm no scientist (at least, no more than a mostly-self-taught-right-minded-but-not-the-most-books-on-the-subject-learned scientist), but my understanding of thermodynamics (as interpreted from folks who ARE scientists) said the exact opposite, over time even if there WAS stratification it would diffuse into consistency. As it's cooling, that may be a different story. But the difference between 21 and 25c isn't enough to explain that difference. That's my thought.

So yeah, it was probably an efficiency issue. I've noticed stratification when reading with a refractometer for pre-boil if I don't stir, which is much like extract. But it's seldom an issue with finished wort.

 

[brewkinger]

It would diffuse into consistency over a period of time, if left in the right environment.
In this case, it's in a fridge where there is active cooling by the process of conduction.
There is also convective cooling occurring within the vessel as warm rises and cool sinks.
His sample from the top of the vessel after removing it from the fridge would have most definitively been of a lesser density.
Had he left it to come to isothermal conditions, it would have become become unstratified.

 

[max384]

I don't think stratification could explain such a large discrepancy in expected OG. However, a last minute brew where a few things went wrong would...

 

[brewkinger]

It was doomed from the start...lol

 

[FatDragon]

I don't think stratification could explain such a large discrepancy in expected OG. However, a last minute brew where a few things went wrong would...

This is probably true, but stratification could explain part of the discrepancy. Nothing really went wrong, it's just that a brew with a kilogram of oats in 5.6 kilograms of total grist doesn't sparge as well as most of my brews but I haven't done this brew enough to know how the difference shakes out. Even if I didn't hit the 1.068 numbers Beersmith gave me, stratification could mean that I ended up higher than the 1.044 my hydro reading gave me.

 

[chickypad]

Thermodynamically speaking, ANY fluid will experience thermal stratification as it cools.
Your sample from the top would be less dense than the layers below it.

Bear with me because I'm not a scientist, but you are talking about the difference in density due to temp stratification, right? But we correct for temp when taking gravity readings. Are you guys actually saying that the sugars in a uniform wort (as one would expect to have at the end of a 60 min boil) diffuse toward the bottom of the pot as it cools so that there is a big enough difference in sugar concentration to explain a 1.068 to 1.044 reading??

 

[Qhrumphf]

Bear with me because I'm not a scientist, but you are talking about the difference in density due to temp stratification, right? But we correct for temp when taking gravity readings. Are you guys actually saying that the sugars in a uniform wort (as one would expect to have at the end of a 60 min boil) diffuse toward the bottom of the pot as it cools so that there is a big enough difference in sugar concentration to explain a 1.068 to 1.044 reading??

That's the gist.

However, I sincerely doubt that if the wort was 25C coming out of the kettle, and dumped into the fermenter and chilled to 20C, that it's going to cause anywhere near the stratification to cause that. I would expect it to be negligible and immeasurable. The difference between 20C and 90C would be a completely different story.

I don't think stratification is the issue here. I'm guessing it was either a mechanical problem (ie hydrometer stuck to the side of the vial, but I'm guessing that's not it), or it was just a low efficiency problem. Stratification is chasing ghosts as far as I'm concerned.

 

[brewkinger]

I'm not sure if the overall range of 1.044 to 1.068 could all be explained due to stratification.
In my original response, I was mainly addressing that it is very possible to have stratification in this sceario.
Especially in a fridge where there is active cooling processes at work.

I will agree that post boil the wort is very homogeneous, but that changes as it starts to cool naturally and even more so if we force the energy transfer.

 

[chickypad]

I guess my question is what is meant by stratification - I thought we were talking about temp stratification, as in the wort on top is warmer so it's less dense. But it sounds like we are talking stratification of sugars, that somehow they diffuse toward the bottom of the kettle as it's sitting there cooling. That doesn't sound like anything I've ever heard of the way sugar solutions behave. Again, sorry if I am using terms incorrectly and it's been a long time since my science classes.

 

[brewkinger]

Both are occurring simultaneously. The warmer less dense wort has fewer sugars versus the lower layers that are more dense and cool.
They are not diffusing to the bottom, as that occurs across a membrane. They are simply sinking to the bottom because they are cooler and more dense. They contain more sugar. The warmer layers (and a single degree of difference in temp is plenty ) rise up and take sugars with them.
The key here is that the conductive cooling is occurring at the bottom for the most part. Faster if it is in a glass carboy and slower in a plastic bucket. So the entire thing cools from the bottom up. There is constantly a large upper layer that is still warmer and therefore the more dense solution is at the bottom.
I can remember in fluid dynamics lab many yrs ago watching the behavior of fluids like hydraulic oil under pressure and temperature. It was fascinating to observe the way that they behaved
I specifically remember an experiment that involved cooling a fluid in a freezer and we tested using glass, steel, plastic and ceramic vessels.
The test chamber had numerous probes that could be adjusted and there were sometimes 5 to 7 degree fluctuations per foot and the upper layers were often very different in composition from the lower layers.

 

[FatDragon]

I guess my question is what is meant by stratification - I thought we were talking about temp stratification, as in the wort on top is warmer so it's less dense. But it sounds like we are talking stratification of sugars, that somehow they diffuse toward the bottom of the kettle as it's sitting there cooling. That doesn't sound like anything I've ever heard of the way sugar solutions behave. Again, sorry if I am using terms incorrectly and it's been a long time since my science classes.

I suppose it's possible that I really did get 61% efficiency, then. This is my second time doing this brew, though a bit different this time around. My first go was 4kg Vienna, 1kg flaked oats ground to flour in a blender (massive doughballs!), 300g Roasted Barley, 100g Black Patent, and 300g raw buckwheat (ground in the Corona mill with the grain) and while I don't have my notes, I believe I got 80%+ efficiency. This time was 3kg Pils, 700g Vienna, 1kg unground flaked oats, 500g Roasted Barley, 150g Black Patent, 400g ground buckwheat. Is it possible that part of the difference could be due to diastatic power (4kg diastatic malt to 1.7kg non-diastatic in the first run, 3.7kg to 2.05kg second time around) or that leaving the flaked oats (not instant oatmeal style) whole may have prevented their conversion in a 60 minute mash?

 

[chickypad]

Both are occurring simultaneously. The warmer less dense wort has fewer sugars versus the lower layers that are more dense and cool.
They are not diffusing to the bottom, as that occurs across a membrane. They are simply sinking to the bottom because they are cooler and more dense. They contain more sugar. The warmer layers (and a single degree of difference in temp is plenty ) rise up and take sugars with them.

I'm sorry if you have to explain this to me like I'm a 4th grader, but I'm still not getting it. I understand that warmer wort is less dense. If the sample in my hydrometer reads 1.060 at 60 degrees, then I heat it to 100* it will read about 1.053, it's less dense. But the sugar content has not changed. If I cool it back to 60* it will read 1.060 again. You're saying the warmer wort rises up, taking it's sugar with it, but the overall sugar content has not changed right? If you cool the sample properly, the SG reading will be accurate. In other words, this warmer wort has not lost sugars to the cooler wort, it's just less dense due to temp. Or am I totally missing the boat?

 

[Qhrumphf]

I'm sorry if you have to explain this to me like I'm a 4th grader, but I'm still not getting it. I understand that warmer wort is less dense. If the sample in my hydrometer reads 1.060 at 60 degrees, then I heat it to 100* it will read about 1.053, it's less dense. But the sugar content has not changed. If I cool it back to 60* it will read 1.060 again. You're saying the warmer wort rises up, taking it's sugar with it, but the overall sugar content has not changed right? If you cool the sample properly, the SG reading will be accurate. In other words, this warmer wort has not lost sugars to the cooler wort, it's just less dense due to temp. Or am I totally missing the boat?

The issue is the potential lack of a representative sample. If you grab a truly representative sample and chill, it doesn't matter, but if more sugars are at the bottom and you grab the top, yada yada same problem as extract with the actual sugars right but the reading is innacurate. Again at this level and temperature gradient I sincerely doubt the difference is at all significant.

 

[FatDragon]

The issue is the potential lack of a representative sample. If you grab a truly representative sample and chill, it doesn't matter, but if more sugars are at the bottom and you grab the top, yada yada same problem as extract with the actual sugars right but the reading is innacurate. Again at this level and temperature gradient I sincerely doubt the difference is at all significant.

Right. The sample, which I'm embarrassed to admit is still sitting on top of my fermentation chamber with the hydrometer floating in it, is reading roughly 11.2p, or something like 1.043. There is no definitive representative sample nor is there a way to get one as the S-04 took off as it is prone to do and has been bubbling through the 8mm blowoff tube at a bubble a minute for at least 36 hours now.

In the short term, it'll make beer and it'll probably be pretty tasty in spite of any screw-ups. In the long term, it's a lost step in the process of trying to develop and dial this in as a house recipe, but the solution for that is to make more beer, so I'm okay with the setback.

 

[jrcrilly]

I'll just have to measure the ABV with the old "how many before I'm hammered" test?

You can do better than that, plus you can verify whether your sample was representative of the wort. Just test the fermented beer with both a hydrometer and a refractometer. The difference will permit you to derive a reasonable approximation of both og and abv. You can use the third calculator on this page: http://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[FatDragon]

You can do better than that, plus you can verify whether your sample was representative of the wort. Just test the fermented beer with both a hydrometer and a refractometer. The difference will permit you to derive a reasonable approximation of both og and abv. You can use the third calculator on this page: http://www.northernbrewer.com/learn/resources/refractometer-calculator/

If I had a refractometer, I wouldn't have this problem in the first place since I would be able to take quick pre-boil and OG samples without worrying about chilling the wort sample . . .

. . . for which reason this might be a perfect time to buy a refractometer. Get the numbers on this brew and improve my data collection for future brews. Good idea, sir!

Better try the "how many before I'm hammered" test as a control sample anyway. All in the name of scientific progress, of course.

 

[brewkinger]

I understand that warmer wort is less dense. If the sample in my hydrometer reads 1.060 at 60 degrees, then I heat it to 100* it will read about 1.053, it's less dense. But the sugar content has not changed. If I cool it back to 60* it will read 1.060 again. You're saying the warmer wort rises up, taking it's sugar with it, but the overall sugar content has not changed right? If you cool the sample properly, the SG reading will be accurate. In other words, this warmer wort has not lost sugars to the cooler wort, it's just less dense due to temp. Or am I totally missing the boat?

You aren't missing the boat, you are spot on in both instances.
Your confusion comes from the fact that each of the scenarios above are independent of each other.
Your hydro sample example above demonstrates that the difference in readings is due to calibration and inaccuracy of the instrument being used to test the sample.
Same amount of sugar but reading changes because of the tool.

In the OP, the issue is more defined.
As this hot liquid cools naturally, different thermal layers form due to temperature and density. As it continues to cool and homogenize, it would become uniform.
But if you could take a sample from the top and the bottom AFTER STRATIFICATION BUT before COMPLETE cooling and then cool BOTH SAMPLES to the same temp of 68 degrees and test, you would find more sugars in the bottom sample.

And I have to concur with Qhrumpf, it probably wouldn't be the entire cause of the problem, but I am sure of the stratification.

 

[chickypad]

But if you could take a sample from the top and the bottom before cooling and then cool it to the same temp of 68 degrees and test, you would find more sugars in the bottom sample.

This is the part of the process I don't understand. It starts as a homogenous wort post boil, how are more sugars transferred to the bottom of the kettle during cooling? I've just never heard of anyone talk about errors on all grain batches from taking samples off the top or the bottom of the kettle with partial cooling. But maybe I should stop derailing the thread. Hope you get it figured out OP.

 

[brewkinger]

After reading my last post, I realized there was an error which I fixed.

I think someone mentioned it above but I think to ALL the threads and posts (usually in the beginners forum) where people are asking about OG discrepancies and we tell them to RDWHAHB and then we ask them if they stirred well after topping off and taking their sample.

It is a basic physical principle that occurs anytime that there is fluids with varying temps.

 

[doug293cz]

After reading my last post, I realized there was an error which I fixed.

I think someone mentioned it above but I think to ALL the threads and posts (usually in the beginners forum) where people are asking about OG discrepancies and we tell them to RDWHAHB and then we ask them if they stirred well after topping off and taking their sample.

It is a basic physical principle that occurs anytime that there is fluids with varying temps.

The problems with SG measurements after top up is that you added water (with zero sugar) to a sugar solution. This is initially an inhomogeneous mixture, typically with low SG near the top and high SG near the bottom. It has nothing to do with temperature gradients. If the mixture is thoroughly mixed, and then subjected to thermal gradients, the weight % sugar in a sample from any point in the vessel will be the same. The SG might be different point to point, but the ratio of sugar to water will be constant. Temperature gradients won't cause concentration stratification.

Think of a black and tan (a thing of beauty if poured correctly.) Now, stir it up well. I challenge anyone to get the layers to separate back to their original separation (even partially) by cooling, heating, or any other process.



I'm with @chickypad on this one.

Brew on

 

[brewkinger]

The problems with SG measurements after top up is that you added water (with zero sugar) to a sugar solution. This is initially an inhomogeneous mixture, typically with low SG near the top and high SG near the bottom. It has nothing to do with temperature gradients. If the mixture is thoroughly mixed, and then subjected to thermal gradients, the weight % sugar in a sample from any point in the vessel will be the same. The SG might be different point to point, but the ratio of sugar to water will be constant. Temperature gradients won't cause concentration stratification.

Think of a black and tan (a thing of beauty if poured correctly.) Now, stir it up well. I challenge anyone to get the layers to separate back to their original separation (even partially) by cooling, heating, or any other process.

View attachment 344592

I'm with @chickypad on this one.

Brew on

While the black and tan is indeed a thing of beauty, it is a bad analogy of the discussion that we are having.
That density stratification is created with BEER and once mixed up would not separate back into its components.
It is not an equal comparison.

I stand by my beliefs, WORT will stratify
Whether it is for thermal or density (or both) reasons.

I offer up THIS thread as proof. The very knowledgeable scientist Martin Brungard himself chimes in on this.

I am with Martin on this one.

 

[doug293cz]

While the black and tan is indeed a thing of beauty, it is a bad analogy of the discussion that we are having.
That density stratification is created with BEER and once mixed up would not separate back into its components.
It is not an equal comparison.

I stand by my beliefs, WORT will stratify
Whether it is for thermal or density (or both) reasons.

I offer up THIS thread as proof. The very knowledgeable scientist Martin Brungard himself chimes in on this.

I am with Martin on this one.

From the thread you linked:

"I just opened up a pint jar of canned wort. Tested the bottom, tested the top, shook it up and tested the middle, waited an hour and tested the top again. All gave me identical numbers."(https://www.homebrewtalk.com/showpost.php?p=3903693&postcount=12.)​

I think what Martin may be observing is an effect due to trub settling out in the BK post-boil/whirlpool. The stuff that settles rapidly obviously has a higher density than the wort, and a sample containing such material would have a higher SG.

Brew on

 

[brewkinger]

From the thread you linked:

"I just opened up a pint jar of canned wort. Tested the bottom, tested the top, shook it up and tested the middle, waited an hour and tested the top again. All gave me identical numbers."(https://www.homebrewtalk.com/showpost.php?p=3903693&postcount=12.)​

I think what Martin may be observing is an effect due to trub settling out in the BK post-boil/whirlpool. The stuff that settles rapidly obviously has a higher density than the wort, and a sample containing such material would have a higher SG.

Brew on

A pint jar of wort would be pretty much homogenous due to it's small volume. A sample from the top is also a sample from the bottom, lets face it we are only talking about 4 or 5 inches at most.
Plus it is already cooled and come to an internal ambient temperature so there is no more thermal stratification.
5 or 10 gallons of wort is much different due to the volume in a bucket or carboy that allows it to occupy 3 to 4 times that distance from top to bottom.
Again, not a equivalent comparison between a pint of fluid and 5 gallons.

On the second topic, a hydrometer and/or refractometer measure a density of DISSOLVED components in a solution (in our case sugar).
The protein coagulants and trub are not dissolved into solution, therefore they have absolutely no effect on the gravity of the wort.

Trust me when I say that it is a basic (although complex) physical property of a fluid.
I must also reiterate that this could potentially be PART of the problem that the OP had. It could very well be attributed to one or more additional portions of his process.

 

[doug293cz]

A pint jar of wort would be pretty much homogenous due to it's small volume. A sample from the top is also a sample from the bottom, lets face it we are only talking about 4 or 5 inches at most.
Plus it is already cooled and come to an internal ambient temperature so there is no more thermal stratification.
5 or 10 gallons of wort is much different due to the volume in a bucket or carboy that allows it to occupy 3 to 4 times that distance from top to bottom.
Again, not a equivalent comparison between a pint of fluid and 5 gallons.

5.5 gal in my BK is only 6-5/8" deep. Not that much more vertical height than a pint jar. I can't see there being huge differences in behavior due to the extra depth.

On the second topic, a hydrometer and/or refractometer measure a density of DISSOLVED components in a solution (in our case sugar).
The protein coagulants and trub are not dissolved into solution, therefore they have absolutely no effect on the gravity of the wort.

I'm aware of the debate on whether or not suspended particulates affect hydrometer readings. I don't remember seeing any conclusive proof one way or the other. I ordered some fumed silica (silicon dioxide nano particles) in order to run an experiment. The particles are small enough that they will stay suspended in water for relatively long periods of time if a proper deflocculant is used. Should have some results this weekend.

Trust me when I say that it is a basic (although complex) physical property of a fluid.
I must also reiterate that this could potentially be PART of the problem that the OP had. It could very well be attributed to one or more additional portions of his process.

I'd be more inclined to trust you if you posted some references that describe experiments showing that homogeneous solutions can spontaneously generate solute concentration gradients due to temperature gradients or gravity (for solution depths of less than one foot.)

Brew on

 

[brewkinger]

5.5 gal in my BK is only 6-5/8" deep. Not that much more vertical height than a pint jar. I can't see there being huge differences in behavior due to the extra depth.

I'd be more inclined to trust you if you posted some references that describe experiments showing that homogeneous solutions can spontaneously generate solute concentration gradients due to temperature gradients or gravity (for solution depths of less than one foot.)

Brew on

On point #1: I am not disagreeing with you, but again an example of how if you pack it into a smaller layer, the stratification will be minimal.

If it has a chance to spread out, the thermal gradients can and will form.
If you put any vessel into a fridge like the OP did, you exacerbate the process and it cools even faster due to cooling from below due to conduction and from all sides due to conduction and convection.
There is even a component that pressure plays a role in this process as the mass of the upper layers push down on the liquid and add to the gradient.

Even the slightest of temp change from layer to layer is enough for the density gradient to be present.

As to point #2:
I stated early on that my education on this subject was long ago at an engineering university.
If I had the textbooks from back then and my lecture notes I would provide them.
But memory is strong and I distinctly remember learning fluid dynamics and specific concepts and equations and rules and laws.
I remember learning that sugar water like sap is considered a miscible liquid involving a suspension of something dissolved up into water. Oceanic salinity and oxygenation were a focus of this.
But the thermal stratification concept is sound and out there for research.
Google "thermal stratification in fluids "
I just did and came across many articles, most of which apply to manufacturing and such but the science is right there.
There is an entire sub category called fluid dynamics to explain how and why fluids behave the way that they do.

It didn't interest me 24 yrs ago and it interests me only slightly more now because I wanted to try and help explain something in an OP.

But that's all it was... trying to help.

I must say that it hurt my brain to try and recall this stuff today. I saw terms like Maxwell model and stuff and started having flashbacks.

 

[FatDragon]

5.5 gal in my BK is only 6-5/8" deep. Not that much more vertical height than a pint jar. I can't see there being huge differences in behavior due to the extra depth.

In this case it was more like 6 gallons in a 6.5 gallon ale pail, probably somewhere around 16-18 inches deep, if that makes a difference.