refractometer

O.K finally got tired of filling the beeker. Decided to get a refractometer.
Cool toy but general knowledge says you can't use it to measure final gravity, only original gravity.

Then I read this obscure article that says you CAN use a refractometer to measure F.G. One catch, the conversion math is far to complicated for mere mortal man. I'll need to buy this CD (that aslo does alot if crap I'll never need) to do it for me.

I've decided to throw myself on the mercy of the court, appeal to the god(s)
of refractometery / specific gravity and seek this elusive knowledge (without paying through the nose for it). Does anyone possess this gravity grail and can ya send me a copy of it?

ROAD MUTANT said:

O.K finally got tired of filling the beeker. Decided to get a refractometer.
Cool toy but general knowledge says you can't use it to measure final gravity, only original gravity.

Then I read this obscure article that says you CAN use a refractometer to measure F.G. One catch, the conversion math is far to complicated for mere mortal man. I'll need to buy this CD (that aslo does alot if crap I'll never need) to do it for me.

I've decided to throw myself on the mercy of the court, appeal to the god(s)
of refractometery / specific gravity and seek this elusive knowledge (without paying through the nose for it). Does anyone possess this gravity grail and can ya send me a copy of it?

Click to expand...

damn i was thining of buying one but...now...i do remeber using one in my observational astronomy class and i remeber just looking through it, and the star would be broken into different wavelenthgs.i dont recall doing the math though...

ROAD MUTANT said:

O.K finally got tired of filling the beeker. Decided to get a refractometer.
Cool toy but general knowledge says you can't use it to measure final gravity, only original gravity.

Click to expand...

That doesn't make any since to me...SG is SG. If it will measure SG before fermenting, then it will measure it after fermentation too. Can you post some of this "general knowledge" so we can debunk it?

Yeah, I'm pretty sure they just measure SG as long as your SG is within range of your refractometer. What they won't tell you is abv (no more than a hydrometer)...you still have to do a relatively simple calculation.

I've been thinking of getting one of the el cheapo China jobbie refractometers of ebay for $15-20...anybody have any experience with those? Worth it? Apparently they have temperature compensation...

I was looking into getting one as well, but after further consideration, just worth filling the beeker.....They don't measure FG from what I can tell, but if you have ProMash software, that does convert it for you with pretty much ease. But is it worth the $60 or more for them, still not sure it is worth it. Still thinking it through more......

You can't measure FG with it, because they are calibrated to measure the amount of sugar dissolved in "pure" water. The alcohol throws the values off. You can adjust the numbers if you know the OG, but it's messy.

El Pistolero said:

That doesn't make any since to me...SG is SG. If it will measure SG before fermenting, then it will measure it after fermentation too. Can you post some of this "general knowledge" so we can debunk it?

Click to expand...

A refractometer doesn't measure S.G. It measures the refractive index of a solution. (i.e. the amount a beam of light is bent when passing through the solution.) In the case of an unfermented wort, the dissolved sugars are about the only thing that affects the refractive index and the S.G, so it's easy to estimate the S.G.
As David_42 said, after fermentation there are still some dissolved sugars, but also alcohol and CO2 that affect the refractive index.. You can do it, but you need to eliminate the CO2 by putting a sample in a blender, or pouring back and forward between two containers, and then apply some fairly complicated formulae.

This as an oversimplification of what acrually happens.

See http://byo.com/feature/1132.html for more detailed information

-a.

This is very cool...from the BYO article ajf linked to:

To calculate your correction value, measure the specific gravity with your refractometer. Then chill a sample of your wort and measure the gravity with a hydrometer.

Click to expand...

So you buy a refractometer so you don't have to use your hydrometer, but you still have to have a hydrometer to calibrate your refractometer...for each batch?

El Pistole said:

This is very cool...from the BYO article AF linked to:

So you buy a refractometer so you don't have to use your hydrometer, but you still have to have a hydrometer to calibrate your refractometer...for each batch?

Click to expand...

The calibration is only necessary to make very small corrections. I (and I suspect most home brewers) don't bother.

The advantages are:
One drop sampling size.
No temperature compensation. (The thermal mass of one drop is so small it can be ignored, and most instruments have built in temperature compensation.) - You can take a drop from the boil and check within a few points in a couple of seconds.
More accurate than a cheap hydrometer if you have poor eyesight.
They don't roll off the counter and smash into thousands of pieces when they hit the floor.
Great for doing what they are designed to do (measuring the sucrose content of fruit).

The disadvantages are:
Not as accurate as a good hydrometer (With good eyesight.)
Good for OG, but not very good once fermenting has started
More expensive.
The one drop sample size is useless for tasting.

-a

ajf said:

The disadvantages are:
Not as accurate as a good hydrometer (With good eyesight.)
Good for OG, but not very good once fermenting has started
More expensive.
The one drop sample size is useless for tasting.

Click to expand...

That's what I read too. So it pretty much go to the bottom of the need-to-have list. I'd be more interested in a PH meter now. But they are even more expensive and require some maintenance. And the probes wear out too.

Kai

ajf said:

The disadvantages are:
Not as accurate as a good hydrometer (With good eyesight.)
Good for OG, but not very good once fermenting has started
More expensive.
The one drop sample size is useless for tasting.

-a

Click to expand...

I've toyed with the idea (since hydrometers are about $20 here). I can just imagine myself licking the refractometer clean.

I have a refractometer and have used it tons. I love it. I measure through fermentation and while I had to learn adjustments and know I am not gett completely accurate readings, it easily gets me in the ball park which is all I am looking for. It is however simply another brew toy.

I have one that I borrowed from a friend of mine and I use it all thru the mash to check my runnings. I think it is an awesome tool and am planning on getting one of my own soon. You can get one on e-bay for under $50.

Ivan Lendl said:

damn i was thining of buying one but...now...i do remeber using one in my observational astronomy class and i remeber just looking through it, and the star would be broken into different wavelenthgs.i dont recall doing the math though...

Click to expand...

That is not a refractometer that is diffraction grading or a prisim.

ajf said:

A refractometer doesn't measure S.G. It measures the refractive index of a solution. (i.e. the amount a beam of light is bent when passing through the solution.)
-a.

Click to expand...

Which is known as the specific gravity of a solution.

Refractometers are most useful for AG brewers, as you can easily do realtime testing of the sparge runoff. One drop cools off immediately and minimizes the wort loss. This lets you know when you've gotten most of the sugars out and can stop. Even if you batch sparge, it can tell you if a third or fourth sparge is worth doing.

If you grow your own apples, or harvest the wild blackberry, a refractometer will tell you when the sugar has peaked in the fruit. Elk and deer seem to just know when the apples are ripe, the trick is to pick the day before the elk strip the trees.

Hydrometers are best for monitoring the ferment.

Originally Posted by ajf
A refractometer doesn't measure S.G. It measures the refractive index of a solution. (i.e. the amount a beam of light is bent when passing through the solution.)

AHammer16 said:

Which is known as the specific gravity of a solution.

Click to expand...

From http://www.robinwood.com/Catalog/Technical/Gen3DTuts/Gen3DPages/RefractionIndexList.html
We can get the refractive index (RI) of water as 1.33283 (at 20 degrees C)
We can also get (from the same source) the refractive index of a 30% sugar solution as 1.38.
From this we can deduce that dissolving sugar in water increases the RI.

If we check http://www.simetric.co.uk/si_liquids.htm
we can see that adding sugar to water also increases the SG.

So now we add some yeast to a sugary solution and allow it to ferment producing ethyl alcohol, and producing ethyl alcohol.

The elimination of the sugar will reduce both the SG and the RI.
But the generation of ethyl alcohol will reduce the SG, but increase the RI.
(Alcohol has a lower SG than water, but a higher RI.)

This clearly shows that the RI and SG are two completely separate properties

-a.

AHammer16 said:

Which is known as the specific gravity of a solution.

Click to expand...

ajf said:

This clearly shows that the RI and SG are two completely separate properties

Click to expand...

Gawd I love a good physics phight.

You are of course, both right. The refractive index and specific gravity are two different things, but in a solution where H2O is the sole liquid one is trivially derived from the other. :rockin:

Ok, so does anyone here actually use a Refractometer to find OG, FG & %ABV? I'm guessing no.... but I could be wrong....

I was a machinist in my younger days and used these alot for checking the water to coolant concentrations. There are several different types so be careful in bargin hunting.

A word to the wise, make sure you know what scale or range you need. If you buy one check the scale. By scale, I mean if you want to measure 0-10% brix, don't buy one 0-50%. It won't be very accurate, you will have to round or guess between lines.

If you can test it with wort do so. Some are really hard to see. You have to look for the refraction line to line up with a scale some times the line is very faint or really fuzzy especially with a cloudy liquid. If you wear glasses definately test it first. Especially one with bi-focals. The better ones are all glass and have good lenses for focusing

If you drop $60 on one and the scale is wrong or you can't read it you'll be PO'd. A $60 dollar one is cheap, I have bought some over $250. I wouldn't spend that much for one unless you did this for a living.

Just my thoughts... never used it in brewing. Also used it to check water in canned corn... at Delmonte.

Basics:

http://www.coleparmer.com/techinfo/techinfo.asp?openlist=D,E,C&htmlfile=Refractometers.htm&Title=Search

For those who are serious.... there is a wine on listed out of many.
http://www.coleparmer.com/catalog/Product_Index.asp?search=refractometers

The wine one..
http://www.coleparmer.com/catalog/product_index.asp?cls=21374&Request=category