Lower than expected OG

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.

kgranger

Small Wave Brewing
HBT Supporter
Joined
Apr 10, 2013
Messages
295
Reaction score
43
Location
Baltimore
Hoping I can get some help troubleshooting an issue with my efficiency. I having brewed on this system in a while, so I am still working out some kinks.
3 vessel E-HERMS system, I use Brewer's Friend for calculations, just brewed a saison and my OG is lower than expected. According to the software, I was hitting all of my numbers spot on, including the pre-boil gravity of 1.044 in 7 gal of wort, and I took a couple measurements just to be sure. I use a steam condenser, so my boil off is pretty low, but according to the software boiling for 90 minutes should get me down to 6 gal, with a gravity of 1.051. 90 min later I am exactly at 6 gal, but after cooling and taking a measurement, OG is 1.042. Boiling longer would bring this down, but I am just confused as to why after 90 minutes of boiling and reduction of wort, I end up with a gravity lower than the pre-boil. I measured with two different hydrometers, and a refractometer, all show the same number in both pre-boil and post. Thoughts?

Here's the recipe:

Boil Time: 90 min
Batch Size: 5.5 gallons (fermentor volume)
Boil Size: 7.01 gallons
Boil Gravity: 1.044
Efficiency: 76% (brew house)

Hop Utilization Multiplier: 1

STATS:
Original Gravity: 1.051
Final Gravity: 1.004
ABV (standard): 6.2%
IBU (rager): 36.23
SRM (morey): 3.26
Mash pH: 5.66

FERMENTABLES:
7 lb - Belgian Pilsner Malt (70%)
3 lb - Spelt Malt (30%)

HOPS:
0.85 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 60 min, IBU: 19.62
1.15 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 30 min, IBU: 14.74
0.5 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 5 min, IBU: 1.87

OTHER INGREDIENTS:
6 g - Gypsum, Time: 60 min, Type: Water Agt, Use: Mash

YEAST:
Fermentis / Safale - Belgian Saison Ale Yeast BE-134
 
As you surmise, it's impossible for those numbers to be correct. A*B must equal C*D.

Are you sure the full volume of wort was thoroughly mixed just before collection?

Also, all your volumes and gravities are corrected for temperature?
 
As you surmise, it's impossible for those numbers to be correct. A*B must equal C*D.

Are you sure the full volume of wort was thoroughly mixed just before collection?

Also, all your volumes and gravities are corrected for temperature?
Temp was corrected. Pre boil was taken from kettles bottom port after a good amount of stirring and settling. Post boil taken from the fermentor after at least 15 min sitting idle.
 
Only gallon gradations? And you hit the marks at 7 and 6 exactly?

My guess is sample collection. Just pitched? Pull another sample from the fermenter? Giving it a good stir won't harm anything.
 
Let's look at your grist. There may lie the key to the unexpected low gravity (OG).
Spelt is a small kernel, similar to wheat, and smaller than barley.
Where did you get the malt, was it milled? Or did you mill it, if so, at what gap width?

Original Gravity: 1.051
I'd get that same gravity, on my system, BH efficiency set to 75%.
 
It doesn't actually matter what the ingredients were, or even what the mash temperature profile was, if 7 gallons of pre-boil wort have a higher SG than the resulting 6 gallons of post-boil wort...

Cheers!
 
[...] boiling for 90 minutes should get me down to 6 gal, with a gravity of 1.051. 90 min later I am exactly at 6 gal, but after cooling and taking a measurement, OG is 1.042.
Did your chiller perhaps leak water into the kettle? That would explain not hitting your FG. But you would have a larger volume in the kettle than 6 gallons.
 
There's something wrong with this picture. Boiling down wort increases gravity. Multiple measuring devices confirmed the "wrong" numbers. So there's an incorrect assumption hiding.

Pre-boil volume was measured in the kettle. If final volume was measured in the fermenter as OP suggests, then it may well be they don't measure equally.

Too, at least some wort was left behind, further bollixing the supposed equality of A*B and C*D as @DBhomebrew succinctly put it.

I recommend that, in the future, @kgranger should measure post-boil volume for this purpose in the kettle, just as pre-boil volume. This will yield a decent accuracy in measuring lauter efficiency. Fermenter volume gets us closer to brew house efficiency.

I guess I'm seeing multiple sources of volume measurement error, even if we accept the gravity measurements. BUT we can't. Either there was stratification in one or both samples, or the final wort was somehow diluted to reverse the inevitable concentrating effect of the boil.
 
Temp was corrected. Pre boil was taken from kettles bottom port after a good amount of stirring and settling. Post boil taken from the fermentor after at least 15 min sitting idle.
What do you consider a "good amount of stirring"? Your symptoms, pre-boil SG higher than post-boil SG, are characteristic of incompletely mixed wort. As you collect wort, and sparge, the highest SG wort enters the BK first, and the lowest last, leaving you with high SG wort low in the BK, and lower SG wort near the top of the BK. It takes much more aggressive stirring than most people think to actually homogenize all of the wort when it starts out stratified.

Brew on :mug:
 
Another thought... about sampling methods.

Using a refractometer to keep track of gravity readings throughout brew day is fast and efficient. But you can't simply take a hot drop of wort out of the kettle and place it on the prism. The reading will be badly skewed due to evaporation of the hot wort.
To get a more accurate reading, a (hot) sample should be taken and quickly cooled to room temps, without allowing for (much) evaporation. One of those plastic bulb pipettes can suck some up a sample, then placed bulb-end down into a beaker with cold water. Dry the outside of the pipette, then shake or invert it to homogenize the sample before putting a drop onto the refractometer prism.

Or take some hot wort out of the kettle with a metal measuring cup and immediately chill it in on ice. There may be some evaporation, so the sample should be large enough, say 1/8-1/4 cup. The deeper the cup and smaller the surface and quicker the chill, the less evap.
 
But you can't simply take a hot drop of wort out of the kettle and place it on the prism. The reading will be badly skewed due to evaporation of the hot wort.
If your refractometer has a clear cover for the prism, drop the wort onto the prism and immediately close the cover onto it. My refractometer readings taken at the boil, then again at fermentation temps correspond nearly exactly the same and the fermentation temp reading matches the hydrometer reading.
 
What do you consider a "good amount of stirring"?
Full amount of wort was in the kettle, coming up to boil temp. The wort at this point should be nearly fully mixed, but I gave it several swirls with a paddle, letting it rest before filling my hydrometer cylinder. There's no way this wasn't mixed enough, unless something about the ingredients caused some sort of serious weight difference between parts of the wort. I let the sample cool to 68 as this is my hydrometers calibration temp. Did this twice just to confirm, then used a refractometer just as a third reading.

I recommend that, in the future, @kgranger should measure post-boil volume for this purpose in the kettle, just as pre-boil volume. This will yield a decent accuracy in measuring lauter efficiency. Fermenter volume gets us closer to brew house efficiency.
I'm doing this exactly. Volume measuring isn't really the issue here, my kettles and fermentor are all marked from the factory. I measured 7 gal exactly pre-boil, just about 6 gal post boil before chilling shrinkage. With tubing and chiller losses, 5.5 in the conical. And these were all the predicted volumes from brewer's friend, taking into account my system that I added as an equipment profile.

I will admit that maybe something happened during my gravity readings, I guess this is what I want to troubleshoot the most, as I am aware the science of boiling wort can't just suddenly be reversed. I've been taking samples for years with hydrometers and refractometers, and know that temperature of the wort, clarity, and ensuring everything is mixed fully, but something went wrong this time, just not sure what it was. Best thing to do would brew up something simple and take readings of everything, I just want to make sure I'm doing everything right.
 
I don't think it's the real problem here, but if you're using the gallon gradations on the side of your vessels, you're not taking very good volumetric data. And you correct those for temp? You're miles away from "exactly" anything.

Can you take a current gravity reading? I think your post-boil is most suspect. Exact or not, the pre-boil volume and gravity plus the post-boil volume are all as expected. It's the post-boil gravity that is so far out of whack. You can confirm with a new sample.
 
I don't think it's the real problem here, but if you're using the gallon gradations on the side of your vessels, you're not taking very good volumetric data.
I agree it isn't 100% accurate, but for the sake of a 5 gal home-brew I don't think it's a huge deal to be .1 gal off. As you say, I don't think this is the problem unless I was off by a quarter gallon or more.
Can you take a current gravity reading?
Fermentation underway, hydrometer sample at 68, currently at 1.039. Unless the yeast absolutely crushed it overnight, I'd say a SG of 1.042 sounds right to me.

I'm leaning more on pre-boil measurements being incorrect. I took it as the temp was ramping up to boil, so probably around 205 or so. With hot break and such, should I be taking the measurements before beginning to heat, or does it not matter? Just to reiterate, the sample was cooled to 68 before actually measuring.
 
It's all guesswork now, eh?

You'll be able to find your actual OG later on. There's a calculator in which you can input current hydrometer reading and not-corrected current Brix reading. It'll spit out the OG. @bracconiere, got a link?
 
With hot break and such, should I be taking the measurements before beginning to heat, or does it not matter?

I pull a pre-boil sample just as it's coming to a boil. First, my BIAB bag will definitely have finished draining. Second, at 212° I know the volumetric temp correction is an easy 4% and my spreadsheet has that figure imbedded in its formulae. Third, the wort is pretty well mixed due to convection currents.

I used to take multiple samples and multiple readings of each of those. Multiple samples right when the bag finished draining @ ~180. Multiple samples right at the top of the boil. Over a few batches I found the readings right at boil to be much more regular and in agreement.

Same thing post-boil. Right at flameout gives me better (more consistent) readings than after chilling.
 
Let's say a .1G tolerance in reading the volume on the side of the kettle. "7 gallons" is anywhere between 6.9 and 7.1G.

Corrected for temp, that's a range of 6.62-6.83G. Not quite 7 gallons exactly.
 
7*44=308
6*42=252
Loss of 56 points.

If it were me, I"d presume I misread 1.052 as 1.042. Or the paper slipped. But you measured 3 times, and with refractometer which doesn't have a slippery paper scale. I'm kinda stumped.
 
7*44=308
6*42=252
Loss of 56 points.

If it were me, I"d presume I misread 1.052 as 1.042. Or the paper slipped. But you measured 3 times, and with refractometer which doesn't have a slippery paper scale. I'm kinda stumped.

That's why I think it's sample collection, not a mistake in gravity reading of the sample. Three different tools might agree with each other, but are they agreeing on what is in itself a mistake?

I like the possibility of a transposition mistake, but OP is probably correct in thinking it didn't go from 1052 down to 1039 in ~18hrs.
 
Hoping I can get some help troubleshooting an issue with my efficiency. I having brewed on this system in a while, so I am still working out some kinks.
3 vessel E-HERMS system, I use Brewer's Friend for calculations, just brewed a saison and my OG is lower than expected. According to the software, I was hitting all of my numbers spot on, including the pre-boil gravity of 1.044 in 7 gal of wort, and I took a couple measurements just to be sure. I use a steam condenser, so my boil off is pretty low, but according to the software boiling for 90 minutes should get me down to 6 gal, with a gravity of 1.051. 90 min later I am exactly at 6 gal, but after cooling and taking a measurement, OG is 1.042. Boiling longer would bring this down, but I am just confused as to why after 90 minutes of boiling and reduction of wort, I end up with a gravity lower than the pre-boil. I measured with two different hydrometers, and a refractometer, all show the same number in both pre-boil and post. Thoughts?

Here's the recipe:

Boil Time: 90 min
Batch Size: 5.5 gallons (fermentor volume)
Boil Size: 7.01 gallons
Boil Gravity: 1.044
Efficiency: 76% (brew house)

Hop Utilization Multiplier: 1

STATS:
Original Gravity: 1.051
Final Gravity: 1.004
ABV (standard): 6.2%
IBU (rager): 36.23
SRM (morey): 3.26
Mash pH: 5.66

FERMENTABLES:
7 lb - Belgian Pilsner Malt (70%)
3 lb - Spelt Malt (30%)

HOPS:
0.85 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 60 min, IBU: 19.62
1.15 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 30 min, IBU: 14.74
0.5 oz - Styrian Goldings, Type: Pellet, AA: 5.5, Use: Boil for 5 min, IBU: 1.87

OTHER INGREDIENTS:
6 g - Gypsum, Time: 60 min, Type: Water Agt, Use: Mash

YEAST:
Fermentis / Safale - Belgian Saison Ale Yeast BE-134
I got a gravity reading of 1.052 for a 5 gallon batch as well. I threw in some amylase to help after 60 minutes, but it was too late.
 
The problem arises with a measurement somewhere either volume or SG what went in is neither here nor there if your per boil SG and volume are correct the post boil volume and SG must agree providing you have lost nothing other than evaporation. You must remember that if you took the volume of the pre boil at high temperature say 70C then there is circa 2-3 % wort shrinkage if the post boil was taken after before chilling so there will be some increase in SG but the volume will have reduced by the same 2-3%. I have never heard of anybody losing sugars during boiling it just cannot happen... unless there is a boil over. Long story short you have made an error in a measurement somewhere be it volume or SG after sparging.
 
Last edited:
I disagree. I took three readings, one after mash, after sparge, after boil. Boil was different, but I didn't take a reading until temperature was about 62F or 63F. the rest I also had to wait before using the hydrometer.
 
I got a gravity reading of 1.052 for a 5 gallon batch as well. I threw in some amylase to help after 60 minutes, but it was too late.

I disagree. I took three readings, one after mash, after sparge, after boil. Boil was different, but I didn't take a reading until temperature was about 62F or 63F. the rest I also had to wait before using the hydrometer.
I can't tell from the context of the thread what point you are trying to make. Can you provide a bit more information?

Brew on :mug:
 
*The rest I had to wait before using hydrometer.

That would have given me an incorrect reading. As in the temperature would, I believe, affected the gravity reading.
 
I disagree. I took three readings, one after mash, after sparge, after boil. Boil was different, but I didn't take a reading until temperature was about 62F or 63F. the rest I also had to wait before using the hydrometer.
You cannot lose sugar during the boiling phase if it was there before the boil started it will be there after it has finished Sooooo you have made an error in either a gravity reading or a volume reading or both.
 
I'm not suggesting that I lost sugar during boiling. I'm suggesting that efficiency is lower because the strike temp is 5 degrees lower. 150 degrees is a low mash temperature for saccharification efficiency. Which is why I would recommend anyone recreating this recipe to mash at 155 fahrenheit to get a better extraction rate, therefore a better gravity reading.
 
150 degrees is a low mash temperature for saccharification efficiency. Which is why I would recommend anyone recreating this recipe to mash at 155 fahrenheit to get a better extraction rate, therefore a better gravity reading.

You should be able to get virtually 100% conversion efficiency, and whatever lauter efficiency is dictated by your equipment and process, at either temperature. IOW, mashing at 150F instead of 155F, won't, in and of itself, cause a hit to mash efficiency. But it will affect fermentability.
 
You should be able to get virtually 100% conversion efficiency, and whatever lauter efficiency is dictated by your equipment and process, at either temperature. IOW, mashing at 150F instead of 155F, won't, in and of itself, cause a hit to mash efficiency. But it will affect fermentability.

Explain IOW. I wonder why there was a documentation of a higher OG at 150F. Something was off from OP, right off the bat. The addition of tannins is all I can think of in terms of affecting fermentability. Steeping my grain for longer will be my next stab at this recipe; not that I care for higher alcohol (I do). Thermal equalibrium makes the temperature go towards ambient levels, which was 62F that day. Explain to me how it would affect fermentability.
 
Explain IOW. I wonder why there was a documentation of a higher OG at 150F. Something was off from OP, right off the bat. The addition of tannins is all I can think of in terms of affecting fermentability. Steeping my grain for longer will be my next stab at this recipe; not that I care for higher alcohol (I do). Thermal equalibrium makes the temperature go towards ambient levels, which was 62F that day. Explain to me how it would affect fermentability.
What's your question? I can't figure it out from the word salad you wrote.

If you want to know how to diagnose mash efficiency issues (typically lower than expected OG) I suggest you read the following post. If there is something in there you don't understand then ask detailed questions ("I don't understand, please explain" is not a useful request for help.)

OP's issue was an OG measurement that was lower than their pre-boil SG measurement. This is physically impossible. If you have measurements like this, your measurements are in error. It's that simple. Before you can diagnose efficiency problems, you have to fix your measurement problems. If the data is bad, you can't use it for problem solving.

Brew on :mug:
 
Last edited:
I don't know what IOW means. He's not making it clear Doug293cz. I have 12# grain to 4 gallons strike water, with 1 sparge water additions.

After overlooking your post Doug293cz, it says that my lauter efficiency is lower overall.

If you are suggesting that I made an error, I would say that I was precise and accurate to the best of my abilities brewing a batch of beer.

Thanks for the input.
 
"IOW" = In Other Words

As @VikeMan implied "conversion" does not necessarily imply a degree of fermentable wort. In theory one could have the same recipe result in a highly fermentable wort or a dreadfully poorly fermentable wort, both with the same degree of "conversion", but with the percentage of dextrins resulting from radically divergent mash temperature profiles making the difference...

Cheers!
 
Explain to me how it would affect fermentability.

Each of the enzymes involved in breaking down starches has a characteristic temperature at which it's most efficient, i.e. where it's able to work fast in comparison to the rate at which it denatures. And, each enzyme works (cuts) at different parts of carbohydrate structures. The result is that the mix of various fully fermentable sugars, partially fermentable sugars, and unfermentable dextrins in the wort depends on the mash temperature (among other things).

For the two temperatures in your example, 150F will, all else being equal, produce a wort that is more fermentable than 155F.

That said, both mashes, if properly executed, will result in the same mash efficiency, i.e. with virtually all of the starches converted to sugars and dextrins, and with the same amount of total carbs (sugars+dextrins) making it into the boil kettle.
 
"IOW" = In Other Words

As @VikeMan implied "conversion" does not necessarily imply a degree of fermentable wort. In theory one could have the same recipe result in a highly fermentable wort or a dreadfully poorly fermentable wort, both with the same degree of "conversion", but with the percentage of dextrins resulting from radically divergent mash temperature profiles making the difference...

Cheers!
That's what it means, thanks a lot!

I did not know that about fermentable wort, thanks for bringing that to my attention.

So its not the temperature of the wort, but the quality of the grain basically. The consistency, or quality of carbohydrates matters for the saccarification to be matched.
 
I have found this thread confusing in the extreme! o_O 🤣
It seems simple enough pre boil and post boil SG x volume did not match two possibilities errors were made in estimating wort volumes or gravities or some wort was lost somewhere ... there are no other ways of explaining this ... what has the mashing got to do with anything ??? That happened before the vols and gravities were estimated o_O
 
So its not the temperature of the wort, but the quality of the grain basically.

In regard to the total amount of sugars and dextrins that can be produced, yes, it's the types and quantities of grains that matter, because they determine the amount of starches available to convert.
 
Using a refractometer to keep track of gravity readings throughout brew day is fast and efficient. But you can't simply take a hot drop of wort out of the kettle and place it on the prism. The reading will be badly skewed due to evaporation of the hot wort.
This is an excellent point. That might explain why my hot samples always have a higher gravity than expected. Thanks, I've never realized that
 
Back
Top