So what's the gravity?

Discussion in 'General Brewing Discussions' started by Donoroto, Jan 9, 2021.

  1. Donoroto

    Donoroto Well-Known Member

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    As an engineer, I thrive on data. So until now I have relied upon my hydrometer, refractometer and Tilt to deliver the Specific Gravity readings on which I rely.

    When I first received my hydrometer - it was a gift - I checked in some water and it read 1.000, as expected. Or, at least I think I did...

    After a few brews, I spent <$20 on The Amazon and got a cheap refractometer. It, too read 1.000 with water; of this I am sure.

    A few brews after that, I splurged on a Tilt. The idea of monitoring a fermentation in real time, as opposed to periodic 8 oz samples, was very seductive. Indeed, watching the fermentation is almost the highlight of my day, when something is fermenting. The Tilt reads 1.000 or 0.999 in water from the tap.

    The problem is none of them ever agree. I get three different answers every single time, and this is very frustrating to me. Last brew, the OG was 1.059 on the hydrometer, 1.058 on the refractometer, and 1.057 on the tilt. No, not a big difference, but...

    FG for that beer was 1.022 on the hydrometer and 1.011 on the tilt. Waugh! What to believe? (Oh, and all are at 60-65 F, I do check the temperature).

    Checking the hydrometer, I got what you see in the photo (1.004 to my eyes) in tap water at 60 F. (It is a 60 F hydrometer). How can this be? Do I just have a cheap instrument, and simply need to spend more to buy a better one? I checked for bubbles in the water, found none. I have half a mind to visit the FLHBS and compare all of their stock to mine. I also wouldn't mind spending $40 on a good hydrometer, but the one I have is a USA-made BSG, I'd expect it to be spot on. Even though it was maybe $10.

    /Rant

    What I plan to do is get some distilled water and create two different sucrose solutions and check the calibration at all three points of all three instruments. Create correction tables for each, and use them every time. But I am open to other suggestions.

    Does anyone have a story of similar experiences? Perhaps with an action plan?
    hydro.jpg Or am I just too worried about 8 thousandths of a gravity point?
     
  2. SabreSteve

    SabreSteve Well-Known Member

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    I believe there's a hyrometer offset option on your equipment profile. Just record your offset there, plug the readings in as you see them and let Brewer's Friend make the correction for you
     
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  3. Herm_brews

    Herm_brews Well-Known Member

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    Maybe check your thermometer - are you using a digital, or analog? If both analog and digital, do they agree?
     
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  4. Group W

    Group W Well-Known Member

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    They are all very sensitive to temperature. Calibrating with distilled water is best.

    I use a refractometer on OG and use the hydrometer on FG. The Tilt is not very reliable for absolute values. It can get a chunk of yeast or hop trub stuck to it and give a false reading. The tilt is a good tool for visualizing the rate of gravity change.
     
  5. thunderwagn

    thunderwagn Well-Known Member

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    I learned a long time ago to pick -one- and be done. Same goes with thermometers and even brewing software. You'll drive yourself senselessly mad. That said, your 3 readings are so close, I wouldn't bat an eye.

    But I'm not an engineer. I'm a tradesman. So I spend my days making things work that engineers designed with data :D
     
  6. Trialben

    Trialben Well-Known Member

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    My thoughts in the hydrometer I rekon that slieve inside moves. I only use hydrometer havnt got around to refractometer which I recon would be cool on brew day for quick gravity reading just to know your on track when mashing.

    I'd buy another hydrometer I had one that's .002 points in water that's a back up now in case I break my other one.
    Good luck
     
  7. Daniel Parshley

    Daniel Parshley Active Member

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    I use a hydrometer and refractometer (BRIX) and do get variable readings, but most are within the variability of the math equations. We are not making very precise measurements. Add to this the alcohol will throw off the BRIX reading a bit, too. You are getting about the same range of readings as I get but it does not bug me so bad that I have a compelling desire to spend $10,000 for super precise lab quality equipment. I spent around $30-40 for two hydrometers and a refractometer and I figure I get what I paid for in data on my brew.
     
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  8. Donoroto

    Donoroto Well-Known Member

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    I should clarify: not a big problem in the grand scheme of things. But I think of Anheuser-Busch and want to have their level of process control. On my budget, of course. Like any engineer.

    But yeah, I guess I need to live in the technical world. Like @Daniel Parshley wrote, close enough is all you need.

    Even though the ABV is somewhere between 5 and 6%, does it really matter? No. It does taste good though...
     
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  9. Donoroto

    Donoroto Well-Known Member

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    I have three, two analog and one digital, they agree to a degree or two. I'm not sure even 10 F off would matter so much to a hydrometer or refractometer. Maybe one gravity point?

    However, I could probably go on a similar rant about thermometers. The three of them are close but they don't always agree, particularly at high temperatures. And don't get me started on the temperature display on the Brewzilla. So just amplify it a little more and I'm in the same place as my specific gravity readings. So what I said above still applies here I guess.
     
  10. Group W

    Group W Well-Known Member

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    I count at least 7 temp gauges in my brew room and would never want to know how different they all are.

    When my pickup was under warranty took it in for a free oil change and told the young man as he was airing the tires to make sure they were above spec or the TPMS light would trip. He said “no problem, I have this nice digital pressure gauge.” I just smiled.:)
     
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  11. Daniel Parshley

    Daniel Parshley Active Member

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    Speaking of
    I was told Anheuser-Busch brews a bit above the target ABV and then adds a bit water to hit the target ABV. I have done the same when adding priming sugar. Usually I can get within 0.10% ABV, IF, and a big if, I have measured my fermentables and water carefully during the brew. I'm amazed how predictive the recipe calculator is on Brewers Friend and it is usually within 0.20% of final ABV. I enjoy playing with all my brew toys and trying to hit a specific ABV.
     
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  12. Hawkbox

    Hawkbox Well-Known Member

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    Same, I use one and trust it. Otherwise I'll be here all day.
     
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  13. Nosybear

    Nosybear Well-Known Member

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    There's an old saying: A man with two watches never knows the time.... Basically at our scale, pick ONE gauge and go with it. You can calibrate a thermometer's freezing point by measuring the temperature of an ice water bath, otherwise, you're dependent on the thermometer's linearity. You can and should calibrate a pH meter every use. You can calibrate a refractometer or hydrometer using distilled water at 60 degrees. Once you've calibrated your instruments, use them. Every measuring instrument has its own accuracy and precision and generally, as stated above, you get what you pay for. I can take three readings of the same sample with my refractometer, even calibrated, and get differing measurements just due to any residual water in the eye dropper.
     
  14. Hawkbox

    Hawkbox Well-Known Member

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    Yeah unless my first reading is wildly out from what I expect I just run with it.
     
  15. BOB357

    BOB357 Well-Known Member

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    I use a lab grade spirit thermometer to check all of my thermometers occasionally, or when I suspect a calibration problem. I use a floating dairy thermometer in the mash and a quick read digital for everything else. Oops. I do monitor mash temperature swings with a dial thermometer via a hole in the lid of my Digiboil, but rely on the dairy thermometer for actual temperature. I'm also checking my various cooking thermometers periodically.
     

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