Author Topic: Hydrometer vs. Refractometer  (Read 4215 times)

Offline ambiorix

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Hydrometer vs. Refractometer
« on: December 04, 2009, 07:18:49 AM »
I'm going to be brewing my first AG batch soon and wanted to know which is the best way to check for starch conversion at the end of the mash, a hydrometer or a refractometer? I've got a small hydrometer that can remain in the mash tun. The guy at the HB shop recommended it, and it certainly sounded better than the iodine test. I have a refractometer as well, but didn't know if that would be more accurate.

Thanks!

Offline bluesman

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Re: Hydrometer vs. Refractometer
« Reply #1 on: December 04, 2009, 07:46:04 AM »
I use a refractometer for measuring the sugar in the mash and wort at pre-boil and flame out. It's quick and easy. You will need a hydrometer to measure your FG because the conversion is a little tricky with a refratometer.
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Offline a10t2

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Re: Hydrometer vs. Refractometer
« Reply #2 on: December 04, 2009, 08:02:01 AM »
Neither a hydrometer nor a refractometer will check for conversion. They can only tell you how much you've extracted. To determine whether or not you have conversion, you need to check that the dissolved solids are sugar and not starches. The cheap 'n' easiest way to do it that I know of is an iodine test.
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Offline theDarkSide

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Re: Hydrometer vs. Refractometer
« Reply #3 on: December 04, 2009, 08:06:39 AM »
I use a refractometer for measuring the sugar in the mash and wort at pre-boil and flame out. It's quick and easy. You will need a hydrometer to measure your FG because the conversion is a little tricky with a refratometer.

Morebeer.com has a spreadsheet that will do this conversion for you, as does most of the brewing software.  I love my refractometer and can't live without it.

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Re: Hydrometer vs. Refractometer
« Reply #4 on: December 04, 2009, 08:10:56 AM »
FWIW I kept track of FG with a hydrometer and a refractometer for five batches. The mean difference between that correlation and a hydrometer reading was 2.4 points and the maximum was 7. I'll use a refractometer to determine when I've reached FG, but not what the FG actually is.
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Offline blatz

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Re: Hydrometer vs. Refractometer
« Reply #5 on: December 04, 2009, 08:38:10 AM »
FWIW I kept track of FG with a hydrometer and a refractometer for five batches. The mean difference between that correlation and a hydrometer reading was 2.4 points and the maximum was 7. I'll use a refractometer to determine when I've reached FG, but not what the FG actually is.

but I've done the same thing over a slightly larger sample size - I think I'm up to 12 batches thusfar, and the FG via hydrometer and refracto after conversion calculation have never been more than 2 points apart and 7 of the samples were clap i-dentical (My Cousin Vinny reference). so why do I continue to compare the two, you might ask?  I like to drink the sample  :-[
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Re: Hydrometer vs. Refractometer
« Reply #6 on: December 04, 2009, 09:29:59 AM »
the FG via hydrometer and refracto after conversion calculation have never been more than 2 points apart and 7 of the samples were clap i-dentical

That's pretty bizarre. The only thing I can think of that might be a factor is that the beers I checked were pretty highly attenuated - IIRC there were all over 80% and the one with the 7 point discrepancy was over 90%. My suspicion is that the correlation was developed using recipes that were all around 75% apparent attenuation, and so it implicitly assumes an alcohol:sugar ratio consistent with that kind of attenuation.

Once I get back to brewing I'm going to start keeping track of both readings again and then maybe we could combine datasets to try to figure it out.
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Offline blatz

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Re: Hydrometer vs. Refractometer
« Reply #7 on: December 04, 2009, 09:34:29 AM »
that's an interesting theory - and actually, all the beers I have done lately are between 73-76% AA, so maybe you're not too far off the mark!
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Offline bluesman

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Re: Hydrometer vs. Refractometer
« Reply #8 on: December 04, 2009, 09:50:48 AM »
I am assuming you have estimated your total starting gravity. Knowing your total gravity estimate and measuring your sugar using a refractometer will enable you to determine your mash efficiency. That would be the easiest and most accurate way to determine your mash conversion.
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Offline denny

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Re: Hydrometer vs. Refractometer
« Reply #9 on: December 04, 2009, 10:06:46 AM »
I'm going to be brewing my first AG batch soon and wanted to know which is the best way to check for starch conversion at the end of the mash, a hydrometer or a refractometer? I've got a small hydrometer that can remain in the mash tun. The guy at the HB shop recommended it, and it certainly sounded better than the iodine test. I have a refractometer as well, but didn't know if that would be more accurate.

Thanks!

You've got a misconception here, as was noted.  Neither of those will tell you about conversion, and you certainly don't want to leave a hydrometer in your mash tun!  You really don't need to worry about conversion....if you mash anywhere from 148-165 degrees for 60 min. or more, you will have conversion.
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Offline bluesman

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Re: Hydrometer vs. Refractometer
« Reply #10 on: December 04, 2009, 10:57:29 AM »
I'm going to be brewing my first AG batch soon and wanted to know which is the best way to check for starch conversion at the end of the mash, a hydrometer or a refractometer? I've got a small hydrometer that can remain in the mash tun. The guy at the HB shop recommended it, and it certainly sounded better than the iodine test. I have a refractometer as well, but didn't know if that would be more accurate.

Thanks!

You've got a misconception here, as was noted.  Neither of those will tell you about conversion, and you certainly don't want to leave a hydrometer in your mash tun!  You really don't need to worry about conversion....if you mash anywhere from 148-165 degrees for 60 min. or more, you will have conversion.

If you read in Palmer's book the section on mashing you'll see that one can determine the mash conversion of starch to sugar based on the grist ratio using a hydrometer.

"extraction efficiency is determined by measuring the amount of sugar extracted from the grain after lautering and comparing it to the theoretical maximum yield. In an optimum mash, all the available starch is converted to sugar. This amount varies depending on the malt, but it is generally 35-ish points per pound per gallon for a 2 row barley base malt. This means that if 1 pound of this malt is crushed and mashed in 1 gallon of water, the wort would have a specific gravity of 1.035. Most brewers would get something closer to 1.031. This difference represents an extraction efficiency of 88%, and the difference could be attributed to poor conversion in the mash, but it can often be explained by lautering inefficiency."

As Palmer has stated one can determine the lautering efficiency which is relative to the actual conversion of sugar in the mash. I find using a refractometer is easier to use than a hydrometer because you only use a few drops of liquor and it's faster. Good Luck.  8)

Ron Price

Offline denny

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Re: Hydrometer vs. Refractometer
« Reply #11 on: December 04, 2009, 10:58:56 AM »
Yeah, I thought about that point of view, but I'm not sure I agree.
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Offline ambiorix

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Re: Hydrometer vs. Refractometer
« Reply #12 on: December 04, 2009, 12:49:14 PM »
I'm going to be brewing my first AG batch soon and wanted to know which is the best way to check for starch conversion at the end of the mash, a hydrometer or a refractometer? I've got a small hydrometer that can remain in the mash tun. The guy at the HB shop recommended it, and it certainly sounded better than the iodine test. I have a refractometer as well, but didn't know if that would be more accurate.

Thanks!

You've got a misconception here, as was noted.  Neither of those will tell you about conversion, and you certainly don't want to leave a hydrometer in your mash tun!  You really don't need to worry about conversion....if you mash anywhere from 148-165 degrees for 60 min. or more, you will have conversion.

I appreciate all of the information and have an additional question. When I'm sparging and measuring the gravity, do I take the hydrometer measurement in the mash (in the sparge water) or do I set aside a wort sample that I've run off to drop the hydrometer in?

Offline blatz

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Re: Hydrometer vs. Refractometer
« Reply #13 on: December 04, 2009, 12:51:12 PM »
When I'm sparging and measuring the gravity, do I take the hydrometer measurement in the mash (in the sparge water) or do I set aside a wort sample that I've run off to drop the hydrometer in?

that.

but I'm not sure what information you're going to get out of that reading, other than what sugars you've left behind, which is inevitable (and why we can partigyle).
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Offline denny

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Re: Hydrometer vs. Refractometer
« Reply #14 on: December 04, 2009, 12:51:54 PM »
Assuming you're fly sparging, you'd set aside a sample long enough to cool before taking a reading.  If you're batch sparging, there's no real reason to worry about your sparge gravity.  IME, it will be fine unless you really get carried away batch sparging!
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