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Old 02-02-2010, 03:17 PM   #1
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Default Spectrophotometry

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.

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Old 02-02-2010, 03:22 PM   #2
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A decent refractometer can be had for less than a hundred with shipping.

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Old 02-02-2010, 03:37 PM   #3
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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.

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Old 02-02-2010, 03:40 PM   #4
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+1 on the refractometer

http://www.austinhomebrew.com/produc...oducts_id=1014

If you wait, he might even put it on sale again...

I'm not sure how easy it would be to measure sugar spectrophotometrically. Maybe measure alcohol concentration with alcohol dehydrogenase...

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Old 02-02-2010, 03:48 PM   #5
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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.

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Old 02-02-2010, 03:50 PM   #6
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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.

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Old 02-02-2010, 03:50 PM   #7
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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.

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Old 02-02-2010, 05:45 PM   #8
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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.

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Old 02-03-2010, 06:25 PM   #9
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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.

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Old 02-05-2010, 07:07 PM   #10
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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.


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