Help me with my gravity readings

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hio3791

hio3791

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Although I've been brewing for a long time and I've dialed everything down I cannot seem to get reliable preboil and postboil gravity readings.

First, the obvious, yes, my hydrometer is calibrated and yes, my thermometers are calibrated and yes, I can take very accurate volume measurements.

I take the preboil readings by taking a cup of boiling wort. It's been stirred since I take the sample after the hot break. I chill the sample in the freezer until it reaches around 60F. I also note the volume at the time I took the sample.

I take the postboil after I recirculate thru my plate chiller and the wort has been brought down to pitch temp so it's thoroughly mixed since I recirculate for the last 15 min of the boil plus however long it takes to chill.

The volumes between both readings differ by approximately a gallon, depending on boil length, boil strength, evaporation, etc.

I started taking pictures of both readings because I thought I was losing my mind.

I brewed an APA tonight. Both readings were taken at 63F., 13gal pre and 11.5gal post.

Pre
View attachment 1467517467074.jpg

Post
View attachment 1467517453549.jpg
 
How vigorously were you boiling and what are using to boil? How are you calibrating your hydrometer? This doesn't make sense at all! I don't think it's scientifically possible to not gain any points during a boil...
 
I might be a noob, but in my opinion, your hydrometer flask is too full, and it looks like (could be an optical illusion) your hydrometer is touching the side of the flask. If none of this matters, please disregard. Actually, please let me know it's of no importance so I can stop worrying about it myself. :)
 
As Sherlock Holmes said; once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.

The hydrometer is touching the bottom of the flask.
 
Sammy86 said:
How vigorously were you boiling and what are using to boil? How are you calibrating your hydrometer? This doesn't make sense at all! I don't think it's scientifically possible to not gain any points during a boil...
Click to expand...

I calibrate it with tap water at 60F. Here's a picture of the boil. I have a 5500 ULWD (eKettle).

View attachment 1467545978421.jpg
 
ScrapRoomBrewer said:
I might be a noob, but in my opinion, your hydrometer flask is too full, and it looks like (could be an optical illusion) your hydrometer is touching the side of the flask. If none of this matters, please disregard. Actually, please let me know it's of no importance so I can stop worrying about it myself. :)
Click to expand...

That's actually an interesting thought. I'm pretty sure the hydrometer isn't touching the flask but I can't rule it out definitively.
 
btbnl said:
As Sherlock Holmes said; once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.

The hydrometer is touching the bottom of the flask.
Click to expand...

That's one of my all-time favorite quotes!

I've wonder if it's possible for a hydrometer to be calibrated, with water at 60F, but off at higher gravities. Could this particular hydrometer be inaccurate at other gravities? If so, then both readings are inaccurate and I have no idea what's the SG of this wort! Worse yet, I can't rely on any past reading! But is this speculation possible?

My friend thinks the hydrometer is alien and that I should get a refractometer. Probably the only thing left to do!
 
hio3791 said:
That's one of my all-time favorite quotes!

I've wonder if it's possible for a hydrometer to be calibrated, with water at 60F, but off at higher gravities. Could this particular hydrometer be inaccurate at other gravities? If so, then both readings are inaccurate and I have no idea what's the SG of this wort! Worse yet, I can't rely on any past reading! But is this speculation possible?

My friend thinks the hydrometer is alien and that I should get a refractometer. Probably the only thing left to do!
Click to expand...


Since the whole concept of a hydrometer is just a weight with air and lines I don't think so? It's not a digital thing like a thermometer where the computer can be screwy
 
Are you sure you got the right pictures? The last one which should be post boil looks lighter than the one that is pre-boil. It may just be the light the pictures were taken in. Or two pictures from slightly different angles of the same sample???


If it is not a picture problem, there is an error somewhere, what it is I can't tell.
Also, if you started with 13 gallons and boiled off to 11.5 gallons it is impossible for the gravity to NOT rise.ble

Try another gravity reading. Preferably before fermentation starts.
 
ok silly question, maybe. but what is the difference between a hydrometer and a refractometer?
 
Out of curiosity, why do you take the sample after the hot break? I know you said you stir it up, so I'm guessing that's not the source of the problem. It just never occurred to me to take the pre-boil sample that far along in the process.
 
the hydrometer has to be bottoming out in the test jar.
& I too recommend checking pbg (pre-boil gravity). I usually pull a sample as soon as I have combined 1st & 2nd runnings, quickly chill the sample & measure gravity. I usually have this done before my wort even comes to a boil.
 
kh54s10 said:
Are you sure you got the right pictures? The last one which should be post boil looks lighter than the one that is pre-boil. It may just be the light the pictures were taken in. Or two pictures from slightly different angles of the same sample???


If it is not a picture problem, there is an error somewhere, what it is I can't tell.
Also, if you started with 13 gallons and boiled off to 11.5 gallons it is impossible for the gravity to NOT rise.ble

Try another gravity reading. Preferably before fermentation starts.
Click to expand...

The pictures are the right ones but each taken from slightly different angles. The light source was behind me and in the first picture I was blocking the light source so it makes the sample look darker.

I agree with what you're saying. It's impossible to have identical readings so where's my problem? I can't figure it out.
 
ScrapRoomBrewer said:
Out of curiosity, why do you take the sample after the hot break? I know you said you stir it up, so I'm guessing that's not the source of the problem. It just never occurred to me to take the pre-boil sample that far along in the process.
Click to expand...

No specific reason actually. Maybe because I saw a guy do it that way when I was starting out.
 
meatcleaver said:
the hydrometer has to be bottoming out in the test jar.
& I too recommend checking pbg (pre-boil gravity). I usually pull a sample as soon as I have combined 1st & 2nd runnings, quickly chill the sample & measure gravity. I usually have this done before my wort even comes to a boil.
Click to expand...

I'll try this next time and I'll make sure the hydrometer isn't touching the flask.

The question is, which reading is right? I'm assuming both are wrong. The OG for this recipe was 1.054. If I take the first reading and extrapolate the SG, it comes out to 1.052 which puts me close to the expected. But if the second reading is the right one, then I missed the targeted gravity by quite a bit.

Now I question all previous gravity readings so how confident can I be of my brewhouse efficiency?
 
You could always make up an extract solution, so that you'd know exactly what the gravity should be, and use that as a cross-check of your measurement process.
 
You may want a taller graduated cylinder for gravity readings with hydrometer too, but there is a calculator on brewers friend. Com for measuring beer (fg) with a hydrometer if you decide to completely forget about the hydrometer.
 
hio3791 said:
No specific reason actually. Maybe because I saw a guy do it that way when I was starting out.
Click to expand...


I am always amazed by how much of my (and apparently other's) brew day is controlled by this sort of thing.

I'd love to see you try a sample before it hits boil, as well as after, although I really doubt it'll matter much.

Also, when you checked its calibration in the tap water, the results were at or around 1.000? Or were they off much?
 
ScrapRoomBrewer said:
I am always amazed by how much of my (and apparently other's) brew day is controlled by this sort of thing.

I'd love to see you try a sample before it hits boil, as well as after, although I really doubt it'll matter much.

Also, when you checked its calibration in the tap water, the results were at or around 1.000? Or were they off much?
Click to expand...


Weird thing is that even if it was completely uncalibrated, it still shouldn't give the same number. All I can think is that it's touching the bottom
 
ThatVideoKid said:
Weird thing is that even if it was completely uncalibrated, it still shouldn't give the same number. All I can think is that it's touching the bottom
Click to expand...

If it was resting on bottom, it would read high - your post boil reading is low.
Maybe it's touching the side of the flask and hanging up, but that really doesn't seem likely. I just don't know.
 
My experience as an analytical chemist hydrometers are only relatively accurate to ±0.001-0.002 SG depending on the brand and your perception.

I'm guessing in your instructions it said that your hydrometer is calibrated rated at 63°F? If so awesome temperature is standardized but it looks like you may have overfilled your testing vessel. Next time try leaving enough space as to not encroach on the rim as it seems like hydrostatic pressure may be messing with the accuracy of your readings and a true meniscus.
 
RevKev said:
Next time try leaving enough space as to not encroach on the rim as it seems like hydrostatic pressure may be messing with the accuracy of your readings and a true meniscus.
Click to expand...


A) WOOT!

B) Who doesn't love the word "meniscus"?!?
 
You really need to take a pre-boil reading before you add any heat to your wort. It is basically after you have your 1st and 2nd runnings out of your mash tun and you have stirred them together, then take your pre-boil readings. After you are done boiling your wort and turned the heat off, go ahead and take your post boil reading.

To me it almost looks like the pictures are flip flopped, as the second one is lighter and less concentrated than the first picture.
 
Less than a week later, the beer is finished. I took 2 readings: one with the jar partially filled and one filled to the rim. The hydrometer reads the same in both instances. For both readings, I submerged the hydrometer and gave it a good spin. I made certain that it wasn't touching or resting against the jar.

View attachment 1468065080613.jpg
 
Hard to see but here's a pic with 70F water, after correcting for temp, the hydrometer reads 1.000.

View attachment 1468068324280.jpg

So what the heck is going on with my pre and post boil readings? The pictures at top of thread were taking over an hour apart as I did a 90 min boil. The only thing plausible is that this hydrometer is inaccurate at some SG range.

Planning to pick up a refractometer in time for next brew.
 
hio3791 said:
Hard to see but here's a pic with 70F water, after correcting for temp, the hydrometer reads 1.000.

View attachment 361415

So what the heck is going on with my pre and post boil readings? The pictures at top of thread were taking over an hour apart as I did a 90 min boil. The only thing plausible is that this hydrometer is inaccurate at some SG range.

Planning to pick up a refractometer in time for next brew.
Click to expand...

Refractometer is smart, as long as it's calibrated with distilled water instead of tap water.

General rule all hydrometers are standardized yet not all standardized hydrometers are calibrated.

I'll attach a link to NISTs overview of hydrometer calibration but unless you paid 80$ for a hydrometer you are likely to receive results greater than ±0.001SG in the order of two or more magnitudes. A calibration report should note where and by how much the instrument varies so you can correct usually in several spots.

http://www.nist.gov/calibrations/upload/sp250-78.pdf
 

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