Finally got a refractometer......I think it is broke!!

[JOHN51277]

Ok.....Rewind 6 years to when i got my first brew equipment, which included a triple scale hydrometer. I still have it and still use it. Well....I decided to check out a refractometer, and bought one from a well known retailer. I got it about 2 weeks ago and calibrated it to "ZERO" with distilled water. I then went to transfer my honey hibiscus wit and robust porter to keg after a few weeks in secondary, and checked the gravity of both.

These readings were WAY off! I took gravity readings 2 weeks prior before leaving for vacation and my porter was at 1.011 on my hydrometer, and now it read 1.032! It can't be, so I took enough to float the hydrometer again and it had hit 1.008 on there. Which is more in line as to where it should be.

The wit was the same way, and was about 0.020 points off.

Am I doing something wrong, or is this thing posessed???

 

[bob1852]

refractometers are only good for pre-fermentation calcs (without conversion formulas).

The alcohol screws up the reading.

 

[JOHN51277]

refractometers are only good for pre-fermentation calcs (without conversion formulas).

The alcohol screws up the reading.

I feel like a dumb***, In all the years, I have never known that! Ya learn something new every day! Well, I am glad I didnt try to explain that to the guys who sold it to me. Can we delete this thread now? Thanks!!

 

[Reelale]

But, there are spreadsheets that can do the conversions for you for FG. I don't know how accurate they are, but a lot of people say they are spot on with hydrometer readings. There are links here if you do a search.

 

[malkore]

I use my refractometer just for brew day efficiency/pitching OG values.

I still drop a hydro in my bucket before I start racking to secondary/keg.

I am just lazy and don't wanna use a spreadsheet/calculator on the refract. FG reading.

 

[Yooper]

Beersmith has a tool for the correction formula. It seems to work ok, but I still use my hydrometer to get FG, and refractometer for preboil SG, and for the OG.

 

[NoNothing]

Correct me if Im wrong, but dont Hydro's give inaccurate readings with alcohol in the mixture as well?

They're still just measuring the SG of the solution and with added alcohol, the SG will drop as the alcohol has a lower SG than water (0.787). So they'll need a calculation to be adjusted post fermentation as well since you're not just measuring sugar and water anymore.

Then again, its early and Im only halfway through my coffee, but Im pretty sure Im accurate, I'd be happy to be wrong.

 

[Reelale]

Kinda, but all the sugars that made the OG higher than water are now alcohols which makes the FG lower (relatively). And since alcohol is less dense than water, the gravity decreases with the amount of alcohol.

 

[NoNothing]

Kinda, but all the sugars that made the OG higher than water are now alcohols which makes the FG lower (relatively). And since alcohol is less dense than water, the gravity decreases with the amount of alcohol.

Right, but we're still getting a greater change than just the sugars missing with the addition of alcohol. So wouldn't the hydrometer reading be off by as much as the refractometer? And calculations would still need to be done?

 

[Reelale]

Since it's not an absolute value, I think it's the change (delta) from OG to FG that the hydrometer is measuring. Without an OG, FG is a meaningless number. It could be reading anything that affects the gravity of water, above or below.

 

[NoNothing]

Since it's not an absolute value, I think it's the change (delta) from OG to FG that the hydrometer is measuring. Without an OG, FG is a meaningless number. It could be reading anything that affects the gravity of water, above or below.

Right, I understand that.

I just thought that the hydro would be off by as much as the refractometer was and both need adjustment for final gravity because of the alcohol in the solution.

 

[Catt22]

Correct me if Im wrong, but dont Hydro's give inaccurate readings with alcohol in the mixture as well?

They're still just measuring the SG of the solution and with added alcohol, the SG will drop as the alcohol has a lower SG than water (0.787). So they'll need a calculation to be adjusted post fermentation as well since you're not just measuring sugar and water anymore.

Then again, its early and Im only halfway through my coffee, but Im pretty sure Im accurate, I'd be happy to be wrong.

Yes, you are technically correct, however, we home brewers typically use the uncorrected FG reading. This uncorrected reading can be used to calculate the apparent degree of fermentation which is simply the ratio of the final hydrometer reading to the OG reading. This gives us a rough idea of the attenuation or IOW, how well the beer fermented out. Most times a 75% drop is considered pretty good. ie, from an OG of 1.080 down to a 1.020 etc.

Using brewing software makes the conversions a snap and will also provide you with the ABV or ABW and the real degree of fermentation.

Most often, we are just checking to see when the beer has finished out or why it is stuck once again at 1.020.

 

[BlindLemonLars]

Morebeer offers a good spreadsheet for calculating SG during and after fermentation, and it works quite well. (I have Beersmith as well, but I prefer the spreadsheet for this task.) It's available on this page, along with a video tutorial.

http://morebeer.com/learn_vids/vids_refract

 

[NoNothing]

Yes, you are technically correct, however, we home brewers typically use the uncorrected FG reading. This uncorrected reading can be used to calculate the apparent degree of fermentation which is simply the ratio of the final hydrometer reading to the OG reading. This gives us a rough idea of the attenuation or IOW, how well the beer fermented out. Most times a 75% drop is considered pretty good. ie, from an OG of 1.080 down to a 1.020 etc.

Using brewing software makes the conversions a snap and will also provide you with the ABV or ABW and the real degree of fermentation.

Most often, we are just checking to see when the beer has finished out or why it is stuck once again at 1.020.

Awesome, I thought I may have been thinking about it wrong all these years haha.

The issue usually only comes up when its a switch to a refractometer from a hydrometer, where I always assumed the conversion was needed for both.

Thanks

 

[Reelale]

^^^ What he said. And also, refractometers are measuring an absolute value, brix. So they need to be calibrated based on a known gravity, and conversion factors applied. Hydrometers are calibrated too, but since they are just measuring the delta between OG and FG, no conversion needed. This is making my head spin a little....

 

[NoNothing]

^^^ What he said. And also, refractometers are measuring an absolute value, brix. So they need to be calibrated based on a known gravity, and conversion factors applied. Hydrometers are calibrated too, but since they are just measuring the delta between OG and FG, no conversion needed. This is making my head spin a little....

Mine too, just trying to make sure I know the right thing, lol.

Sorry if I confused anyone

 

[JOHN51277]

Im still confused!

 

[Catt22]

Im still confused!

About what?

Here's a re-cap of what everyone is trying to say. Maybe this will help.

1. You can use a refractometer to measure your gravity anytime before the wort begins to ferment. ie before you pitch the yeast. You will still need to use either a formula or some brewing software to accurately convert Brix to SG, but simply multiplying Brix X 4 is a good approximation and that's what many of us do. You can also google up tables that you can print out that will list the correlation.
2. You can take both hydrometer and refractometer readings after fermentation has begun and plug those numbers into formulas in order to determine your OG if you forgot to measure it before the start of fermentation. Some brewing software will have a utility to do the calculation for you.
3. A refractometer reading after fermentation has started will be of no use unless you also take a hydrometer reading at the same time. This is due to the presence of alcohol in the wort which skews the reading.
4. A hydrometer reading taken after fermentation has begun will also be erroneous due to the presence of alcohol in the wort, however, consecutive readings which do not vary over several days is an indication that the fermentation is complete. This same reading can provide you with the apparent degree of fermentation if you divide the FG by the OG points, subtract the result from 1 and multiply by 100 to get a percentage. ie, for an OG of 1.080 and FG of 1.020 it would be: 1-(20/80)X100 or 75% ADF (Apparent Degree of Fermentation). It is called apparent because it is not the real degree of fermentation, but it is still useful as a rough approximation of how well the wort finished out.

So, use your refractometer while sparging to check the runoff gravity in order to avoid oversparging. Use it again at the beginning of the boil to help predict your gravity at the end of the boil. Taken during the boil, if the gravity is not where you want it to be, you can dilute the wort to lower the gravity or you can add malt extract to increase it. You can also boil the wort longer and concentrate it more, but then you may not have the final volume desired. The beauty of the refractometer is that you can take readings quickly using only a few drops of wort. You also don't have to wait for the sample to cool as you would need to do when using a hydrometer. I like to take a hydrometer sample at the end of the boil as a cross check against my refractometer. They usually agree within a point or so and this is then my official OG of record. After that, I just take hydrometer readings at the end of the ferment to see how well the wort finished out. I routinely allow a full two weeks for the beer to ferment in the primary, and normally this is plenty of time for it to finish out with maybe an occasional exception for a very high gravity beer.

 

[Sawdustguy]

You also don't have to wait for the sample to cool as you would need to do when using a hydrometer.

Catt,

Is that really true? The instructions that came with my refractometer say to let the sample cool for about 10 seconds. Maybe it's because a sample that small cools very quickly. Granted the pipet sample size will not take nearly as long as you would have to wait for a theif of wort to cool for a hygrometer reading.

 

[lazybean]

A refractometer and a Hydromiter measure two different things.

A refractometer measures a ratio of the speed of light in a vacuum relative to that speed through a given medium. ours use a scale of Brix which is based on a sucrose solution. the refraction of light through alcohol is so different then pure sucrose, we have to use a correction chart to compensate for it.

A Hydrometer measures Specific Gravity, that is, the ratio of the density of the liquid to the density of water. So there is no compensation needed, since it is directly measuring the SG.

What is different is using the OG and FG to calculate the ABV, since the wort is never converted 100%, or even 100% to alcohol.

Hope it helps, i did a lot of reading on Wikipedia when i first got my refractometer trying to understand how the dang thing worked.

 

[Catt22]

Catt,

Is that really true? The instructions that came with my refractometer say to let the sample cool for about 10 seconds. Maybe it's because a sample that small cools very quickly. Granted the pipet sample size will not take nearly as long as you would have to wait for a theif of wort to cool for a hygrometer reading.

Well, I see no need to let the sample cool when using a refractometer. I figure that the few drops on the face plate will nearly instantly cool to the temperature of the instrument and that would be about how long it takes me to raise it up to eye level and peer through it. As I mentioned, I typically take both a hydrometer reading and a refractometer reading at the end of the boil as a cross check and they usually agree withing a point or so. I do have to wait for the hydrometer sample to cool completely to room temp in order for it to read right without using a temperature correction factor. Boiling wort is supposed to be about 4% less dense than room temperature wort. It shrinks about that much as it cools down. So, in theory, the wort would be less dense at very high temperatures, but I can't see it remaining that way but for a few seconds once it hits that face plate. You could easily verify this for yourself. Take a reading as fast as you can and take another with using the 10 second or longer waiting period. My guess is they will be the same. The trouble with that is that sometimes you will get a slight variance with consecutive readings due to stratification of the wort, suspended hop, trub and break material in the sample and such. I usually take several reading with the refractometer and keep sampling until I get a couple to agree closely. I usually take multiple samples and volume measurments during the boil (often just to kill some time), and I use this in attempt to predict my OG. By the time I actually get there at the end of the boil, I'm usually very close to my predicted gravity.

 

[Catt22]

A refractometer and a Hydromiter measure two different things.

A refractometer measures a ratio of the speed of light in a vacuum relative to that speed through a given medium. ours use a scale of Brix which is based on a sucrose solution. the refraction of light through alcohol is so different then pure sucrose, we have to use a correction chart to compensate for it.

A Hydrometer measures Specific Gravity, that is, the ratio of the density of the liquid to the density of water. So there is no compensation needed, since it is directly measuring the SG.

What is different is using the OG and FG to calculate the ABV, since the wort is never converted 100%, or even 100% to alcohol.

Hope it helps, i did a lot of reading on Wikipedia when i first got my refractometer trying to understand how the dang thing worked.

Well, sort of yeah, but a refractometer doesn't measure the speed of light though anything. Basically what a refractometer does is refract the light through a prism and project it onto a translucent plate with graduations calibrated to a percent sucrose scale. IOW, it measures the gravity indirectly, not that there's anything wrong with that. A hydrometer works on a displacement principle. Liquids of higher density will float the boat higher and the boat in this case is the hydrometer. The side of the "boat" is hopefully calibrated with a scale corresponding to the density of the liquid. The hydrometer doesn't care what the makeup of the liquid is and it can't know. That's where us talking apes come in handy. We've devised a way to correlate the density of the mostly sugar water with the gravity reading. We brewers typically assume that what we are taking the measurement of is mostly sugary wort with some minor amounts of other gunk mixed in. It's good to keep in mind that the ancients made beer without the benefit of thermometers, hydrometers or refractometers, but I would also bet that more often than not, it was pretty much swill. Still, some crummy beer is better than no beer at all I suppose. I've been there for sure.

 

[mattd2]

Well, sort of yeah, but a refractometer doesn't measure the speed of light though anything. Basically what a refractometer does is refract the light through a prism and project it onto a translucent plate with graduations calibrated to a percent sucrose scale. IOW, it measures the gravity indirectly, not that there's anything wrong with that.

Not that I have a refractometer but as I understand it a refractomer works by light shining through the sample at various angles, depending on the what is in the sample at a certain angle the light will stop traveling completly through the sample and refract (or is it reflect?) back, which is seen as the dark line in the eyepiece. Light will travel and refract through alcohol different to water and this is why the measurment is out of wack when taken after fermentation. Someone tell me if I don't know what I'm talking about though:cross:

 

[Catt22]

Not that I have a refractometer but as I understand it a refractomer works by light shining through the sample at various angles, depending on the what is in the sample at a certain angle the light will stop traveling completly through the sample and refract (or is it reflect?) back, which is seen as the dark line in the eyepiece. Light will travel and refract through alcohol different to water and this is why the measurment is out of wack when taken after fermentation. Someone tell me if I don't know what I'm talking about though:cross:

I think your explanation is probably closer than mine was. It makes sense that there is a cutoff of some kind in the instrument which creates the sharp delineation line that we read. There's also a prism in there of some kind, but I'm not sure if it is used simply as a mirror or if it does something else too. I used to think it was just magic of some kind, but now I know better.

 

[mattd2]

I think your explanation is probably closer than mine was. It makes sense that there is a cutoff of some kind in the instrument which creates the sharp delineation line that we read. There's also a prism in there of some kind, but I'm not sure if it is used simply as a mirror or if it does something else too. I used to think it was just magic of some kind, but now I know better.

Yeah as I said I don't own one (would like to one day) so i don't know all the inner works. Sometimes I think it would be easier to explain everything with "it's magic", so far this works well with my 3 year old but I don't know how long that will last