Refractometer question

[ayoungrad]

What is the basis of a brewhouse correction factor?

For my hydrometers (I have one high grav and one more accurate low grav) I use temperature correction and calibration correction only.

 

[br1dge]

I love my refractometer. As everyone else has said it cuts down on the waste and lets me take more measurements very quickly. Its nice to have a hydrometer around every once in a while but I would definitely recommend using a refractometer if you dont currently.

 

[BeerIsDelicious]

I have an app in review by apple at the moment called RefracTool, that will do the work of the spreadsheets linked to in this thread -- check for it in a week or so. I originally made it just for myself, but it's helped me greatly so I decided to spruce it up a bit and release it to the masses.

 

[vanwolfhausen]

I calibrated mine 3 times and is always 5points lower than my hydrometer.

 

[HairyDogBrewing]

What is the basis of a brewhouse correction factor?

One Brix is 4 gravity points - for sucrose.
The refractometer is off a little bit for wort, so there is a small correction factor.
So if you take OG with both hydro and refract you'll see what correction is needed and put that number in BeerSmith's refractometer tool.

I think Yooper helped to develop this, so maybe she can explain it better than I can.

 

[williamnave]

I'm planning on using both at first. How far off was the refractometer? Inherently it seems that the correction would be accurate. Which correction did you use?

5-10 points. My experience was a little limited, but I was steered towards my current methodology by very experienced brewers whose opinion I value.

I found that I could take readings up to a point with a refractometer, and then they would spike when alcohol content got too high.

i.e. OG 1.065

2 days later 1.052

4 days later 1.038

6 days later 1.024

8 days later 1.041

Now, unless there's some serious funny business going on, sugar didn't immaculately conceive itself in my fermenter. I experienced this across quite a few brews, each time taking brix readings, plugging them into BeerSmith, and getting SG out. As I came to understand it, when the alcy content reaches a certain point, the refractometer gets a little unpredictable. Even the most perfect model designed by a MIT hit squad wouldn't be as reliable as floating a hydrometer in it. I now leave my beers in primary for a month or more, and take a FG reading prior to kegging just to make sure all went well.
:fro:

 

[jkarp]

I'm planning on using both at first. How far off was the refractometer? Inherently it seems that the correction would be accurate. Which correction did you use?

Doesn't matter. Refractometers measure brix - a measure of the sugar content of an aqueous solution. After yeast convert the sugars to alcohols, which have entirely different refractive properties, brix refractometers are as effective at determining gravity as sundials. Yes, people have tried to formulate "corrections" for alcohol. Yes, they all suck as anyone who's done side-by-side tests know. Still, refractometers are great for pre-fermentation measurements.

 

[el_kirk]

Yes.
Yes.

 

[a10t2]

A couple things:

The refractometers that have SG scales (at least all the ones I'm aware of) aren't correct. The manufacturer(s?) used the "multiply by four" rule instead of actually putting in a conversion.

They're calibrated for sucrose solutions, but wort is primarily maltose. Typically you convert by dividing by 1.04 - so a reading of 20°Bx means the SG is actually about 19.2°Bx (1.079).

After fermentation starts, the alcohol in solution will result in an artificially high SG reading. You can try to compensate using an empirical correlation. There are two that I know of: one is included in ProMash, BeerSmith, the MoreBeer spreadsheet, etc. I recently developed the other. Everyone I know of who's tried both has found the standard correlation to be less accurate.

http://seanterrill.com/2011/04/07/refractometer-fg-results/

 

[Octavius]

... I recently developed the other...

Many thanks for posting - it looks interesting reading. Can you tell me where the magic number 1.04 originally came from? Or provide a web link, wherein I may educate myself.

Cheers!

 

[ayoungrad]

A couple things:

The refractometers that have SG scales (at least all the ones I'm aware of) aren't correct. The manufacturer(s?) used the "multiply by four" rule instead of actually putting in a conversion.

They're calibrated for sucrose solutions, but wort is primarily maltose. Typically you convert by dividing by 1.04 - so a reading of 20°Bx means the SG is actually about 19.2°Bx (1.079).

After fermentation starts, the alcohol in solution will result in an artificially high SG reading. You can try to compensate using an empirical correlation. There are two that I know of: one is included in ProMash, BeerSmith, the MoreBeer spreadsheet, etc. I recently developed the other. Everyone I know of who's tried both has found the standard correlation to be less accurate.

http://seanterrill.com/2011/04/07/refractometer-fg-results/

Awesome. Thanks for the link. I'll definitely be incorporating that into my spreadsheet.

 

[HairyDogBrewing]

One Brix is 4 gravity points - for sucrose.
The refractometer is off a little bit for wort, so there is a small correction factor.
So if you take OG with both hydro and refract you'll see what correction is needed and put that number in BeerSmith's refractometer tool.

I think Yooper helped to develop this, so maybe she can explain it better than I can.

Follow up:
In BeerSmith it's called "Wort Calibration Value".
For instance, if the refract reads 15.0 Brix and the hydro reads 1.059 (after temperature correction); then the WCV would be 1.04.

 

[a10t2]

Can you tell me where the magic number 1.04 originally came from?

I don't know who would have been the first person to point it out, but the concept of a wort correction factor is pretty well established: http://www.byo.com/stories/projects-and-equipment/article/indices/29-equipment/1343-refractometers

Whether or not it will turn out to be 1.04 for your worts is something you can only determine by taking measurements. 1.04 is just a reasonable average.

 

[bgruis]

Absolutley Yes...great investment

 

[Octavius]

Sean,
Thanks for the link re: the wort correction factor.
Cheers!