Spectrophotometry

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jim_reaper1066

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I have always tracked my beer and wine fermentation using a hydrometer, however I want to take more precise measurements and not drop a few hundred bucks on a refractometer. Does anyone know if a spectrophotometer can be used to track the progression of fermentation in either beer/wine/mead? And if such nm wavelengths can be related back to sugar content? i.e. S.G.? I realize that several different measurements would have to be taken, OD660 nm for yeast cell turbidity, and possibly a spectral scan of different volumes of dissolved sugars in water to establish a background OD. Has anyone ever heard of something along these lines. Im considering taking small volume samples of my next batch of mead to track spectrophotomerically in the lab, it might be a fun experiment to track Hydrometer readings vs. Yeast cell turbidity vs. sugar absorbance.
 
A decent refractometer can cost about 30 bucks, and not much more for shipping. Many of us got ours at the 2 sales that Austin Homebrew did late last year. IIRC it was 26 bucks plus 6 for shipping.

You must already have access to a spectrophotometer, since they run around $23500.00, and that's considerably more than even 100 bucks for a refractometer.
 
I have been out of school for a long time - but don't spectrophotometers suck at quantification - they are mainly used for identifying the presence or absence of a molecule - No?

I have a refractometer that I got off ebay - made in China, works like a charm.
 
A properly calibrated lab-grade spec is very accurate and can certainly be used for quantifying compounds. It is just a question of using the right tool for the job though.
 
Not aware of a spectrophotometric method of determining extract. In commercial breweries, gas chromatography is used, or increasingly specialized instruments. If you have a gas chromatograph, see the methods of the ASBC.

A spectrophotometer can certainly be had less for $24,000. Thats kinda like saying cars cost $100,000.
 
Thanks for the heads up on the cheap austin homebrew refractometers. The only price experience i had was with scientific ones from companies like fisher and sigma, which are a bit overpriced id say.

The use of a spec was really only one of curiosity. I work in a microbiology lab doing research on the bacterial equivalent of the Ehrlich pathway, which is responsible for fusel alcohol production in yeast. I do lots of bacterial growth curves with a nice fully robotic ($ 60,000+) spec, and know the same is done with yeast. Both organisms have well defined lag, logarithmic, and stationary phases of growth so I though it would be fun to track my yeast growth. The ultimate combination of a science nerd and homebrew freak.
 
A spec. won't do the job, most sugars refract light, but they don't absorb it. If one is doing HPLC of sugars you need to have an RI detector (refractive index) not a UV spectrophotometer - which is good for compounds with aromatic (ie double bond containing) rings.
 
Hydrometers do a good job. For measuring worts while brewing, most craft brewers use hydrometers that are designed for a narrow gravity range of thes beers they brew. This gives them more precise readings. Many home brewers use a refractometer due to smaller sample size. With a refractometer you are converting Brix to SG so I would not think this would necessarily be a more precise measurement over the hydrometer. One way of measuring SG, Plato or Brix that is more precise is with a density measurement like used in an Anton Paar instrument. This takes a sample of wort and determines the gravity, Plato or Brix. On finished beer a more complex model can determine many things such as OG, FG, apparent extract, ABV, ABW, etc. But, depending on the model these instruments can run anywhere from $4000 - 50,000.


Dr Malt
 
So we want an instrument that will very precisely measure SG in the beer (not wine) range and we want to take a minimal sample - say max 0.5 ml; to avoid waste of a small batch, minimize temperature problems and reduce instrumentation needed while doing a sample.

Ideally this would also be cheap.

I think the answer would be a hydrometer but calibrated in a range from around zero to whatever the density of of high gravity wort would be BUT it would be made to measure a DILUTION of wort.

IE. Take 0.5 ml of sample and mix into 200ml of pure water (this would elimiate problems with cooling the sample - just use the right temp of dilution water). The hydrometer would be calibrated to measure only in this dilute range.
 
I wouldn't go with a dilution, I'd simply make a thinner sample tube, maybe like those hydrometers for measuring antifreeze.

AK4121.jpg


You could calibrate the tube for each of the balls (sink/float) to get big divisions, and then interpolate values between depending on how much the partuicular ball floats.

My current hydrometer works fine for me.
 
Hydrometers do a good job. For measuring worts while brewing, most craft brewers use hydrometers that are designed for a narrow gravity range of thes beers they brew.

And I have found these to read within 0.1 °P of the much more sophisticated digital densitometers.
Many home brewers use a refractometer due to smaller sample size. With a refractometer you are converting Brix to SG so I would not think this would necessarily be a more precise measurement over the hydrometer.

There are many pitfalls in using refractometers. They often read very close to what a hydrometer does but sometimes they are off by 1 or more Bx. Problem is that you don't know if the sample you are measuring is one of those that is off by a country mile or one that is more nominal.

One way of measuring SG, Plato or Brix that is more precise is with a density measurement like used in an Anton Paar instrument. This takes a sample of wort and determines the gravity, Plato or Brix. On finished beer a more complex model can determine many things such as OG, FG, apparent extract, ABV, ABW, etc. But, depending on the model these instruments can run anywhere from $4000 - 50,000.

The DMA 5000 M is around $22K and will measure all those parameters (though the ABW and ABV measurements are done on distillate and the TE measurement of the residue from the distillation). Add the Alcolyzer module, an automatic sampler and the gas module and now you have a $50 - $60K investment but there is no need for distillation. A great savings in time (if you have the extra $40K.

The DMA 35 is a handheld instrument that uses the same physics but is much less expensive ($2K? - the rep asked if he could come pitch these to my home brew club!) and less accurate (three decimal places rather than the 5-1/2 in the DMA 5000).

A decent spec can be had for a couple thou and they have many uses in the brewery lab
- Water analysis
- Beer bitterness (UV)
- Hops alpha and beta acids (UV)
- Beer color
- Diacetyl
- FAN
- Alcohol (at very low levels)
- Lactic Acid
...

but alas, not extract or sugars.
 
While you're spending the cash, why not invest in a good UV-vis and an NMR? :)
 
I did see data once from a spectrophotometer that gave the quantity of the individual sugars which was interesting; of course the RDF could be calculated from that. This same reference also showed that regardless of the RDF, the ratio of the different sugars relative to one another was the same. Specifically, glucose, fructose, sucrose, maltose, and maltotriose.

Curious, why would you want to do this considering the complexity, cost, time to set up/run samples?
 
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