Refractometers and final gravity

[Katman]

Hi all
I got a refractometer a couple of weeks ago and have been using it to check the OG of a few brews now. I really like it and find it much easier to see than a hydrometer. However I was reading a home brewing book yesterday that seemed to said refractometers are pretty much useless for brewing especially for measuring FG because the alcohol content will throw off the reading and I was wondering if there was any truth to that.

 

[homebrewfinds]

That used to be true, but not anymore. There are calculators that help will help you figure this. My favorite is Sean Terrill's... http://seanterrill.com/2012/01/06/refractometer-calculator/

 

[Qhrumphf]

People swear by the calculators and they do seem to be quite accurate. I personally prefer a good old narrow range hydrometer.

As long as you're comfortable with a calculated indirect measurement, there's nothing wrong with it.

 

[balrog]

I always measure FG with "finish" hyrdrometer (only goes to 1.040 max, giving easier to read expanded scale), but the refractometer seems to be fairly good over recent batches

 

[wallyLOZ]

I started out using a refractometer, but got a hydrometer after all of the online talk about accuracy. Compared the two over several batches, and couldn't see much difference. I'm back to he refractometer. I've used other calculators, but keep going back to the one on Northern Brewers website.

 

[Katman]

Thanks for the replies everyone. Somehow I missed out on the fact that you have to use a calculator to measure the FG. I did a few test last night to compare my hydrometer and refractometer and using the calculator and they seem to give me about the same readings now (close enough for me anyway). Thanks again

 

[Silver_Is_Money]

The refractometer research of Petr Novotny has far eclipsed that of Sean Terrill, and a Novtny based FG calculator will give far more accurate refractometer based FG readings.

 

[Big Monk]

The refractometer research of Petr Novotny has far eclipsed that of Sean Terrill, and a Novtny based FG calculator will give far more accurate refractometer based FG readings.

Only way to know that is to have the data to back it up. Do you have data on your batches to back up a claim for Novotny's calcs?

My data says Terrill Cubic is the most accurate for my batches. It's very easy to put together a tracking sheet for all 4 correlations in excel for comparison.

 

[Silver_Is_Money]

Only way to know that is to have the data to back it up. Do you have data on your batches to back up a claim for Novotny's calcs?

My data says Terrill Cubic is the most accurate for my batches. It's very easy to put together a tracking sheet for all 4 correlations in excel for comparison.

I'm going primarily on Novotny's own work and comparison data. I have made my own spreadsheet utilizing Novotny's quadratic method (wherein, just as for Terrill he offers a more simple linear method as well), though admittedly I have only done a scant few actual checks of my own. As I recall, forum member @dmtaylor has actually done extensive comparisons and it is he who initially inspired me to make the switch. I'm hoping he will chime in here with comment.

Nvotony's article on his refractometer research into beer FG's is published in Zymurgy's July/August 2017 issue. I just noticed that Brewer's Friend has switched their online calculator over to one of Novotny's formulas.

PM me and I will email you a copy of my Novotny quadratic method based calculator.

 

[Big Monk]

I'm going primarily on Novotny's own work and comparison data. I have made my own spreadsheet utilizing Novotny's quadratic method (wherein, just as for Terrill he offers a more simple linear method as well), though admittedly I have only done a scant few actual checks of my own. As I recall, forum member @dmtaylor has actually done extensive comparisons and it is he who initially inspired me to make the switch. I'm hoping he will chime in here with comment.

Nvotony's article on his refractometer research into beer FG's is published in Zymurgy's July/August 2017 issue. I just noticed that Brewer's Friend has switched their online calculator over to one of Novotny's formulas.

PM me and I will email you a copy of my Novotny quadratic method based calculator.

I have my own. I'm just saying that my own batches show Terrill cubic as closer.

 

[Silver_Is_Money]

I've gotten spoiled. On my last two batches i didn't even break out a hydrometer.

 

[balrog]

I can't not measure with finishing hydrometer, regular hydrometer, refactometer

(The first step is to admit you have a problem)

 

[Big Monk]

I've gotten spoiled. On my last two batches i didn't even break out a hydrometer.

I've just incorporated a calculation into my volume tracking scheme that accounts for number of, and size of, my hydrometer readings. That way I have the extra fermenter volume so I still hit my numbers.

I'm not against the refractometer for brewday but I feel more comfortable with a hydrometer for fermentation readings.

 

[dmtaylor]

So far I've got 9 batches with good OG & FG data where I calibrated each instrument every single time it was used. Arguably, 9 data points isn't enough to draw final conclusions and remains work-in-progress. But what I can say is that Novotny is showing to consistently read within 0.001 of a hydrometer (actually 0.0008), whereas Terrill is good to about 0.002. On the graph below, goal is to be right on the light yellow diagonal line -- whoever comes closest is most accurate.

Is Terrill's set of equations good? Sure they are. Is Novotny better? My recommendation is to use your own data and draw your own conclusions. Both come really really close on almost every batch, close enough that for most people it really doesn't much matter which one is better than the other.

Furthermore I should mention that Mr. Sean Terrill and I have discussed and kinda sorta maybe almost can agree that his equation might be better suited where FG ends up being less than about 1.014, whereas Novotny is better above that point, and almost every bit as good as Terrill below that point. Reference:

https://www.reddit.com/r/Homebrewing/comments/bs3af9/sean_terrills_website_issues/

Happy calibrating, calculating, and comparing!

 

[Big Monk]

Furthermore I should mention that Mr. Sean Terrill and I have discussed and kinda sorta maybe almost can agree that his equation might be better suited where FG ends up being less than about 1.014, whereas Novotny is better above that point, and almost every bit as good as Terrill below that point.

Which explains why they seem to align with my batches more.

 

[dmtaylor]

Which explains why they seem to align with my batches more.

BINGO! Now let's all everybody gather round and sing Kumbaya!