Activated carbon and sulfite and RS testing?

Joe Sallustio wrote "My reds almost always come up as 0.3 or .0.4 RS and they sure seem dry. I was wondering if the color or phenol in red may affect Clinitest."

Interesting point Joe. I haven't tested for RS with Clinitest but some of my wine club friends do. If Clinitest is specific for glucose and we are testing wine containing at least some intact sucrose there may be a problem. I've been playing around with a diabetic Glucometer Elite tester as an alternative to Clinitest (some wine club members make sparkling wines and are especially concerned with RS). The method I've been using calls for acid treatment of the wine sample to hydrolyze sucrose to glucose and fructose. The meter then reads glucose and I multiply the answer by a factor to arrive at RS. You would think that sucrose in wine would hydrolyze to glucose and fructose due to the low pH. But, I get very different RS results with and without the acid treatment. You might look into this as part of the problem you've been having with Clinitest.

Bill Frazier Olathe, Kansas USA

Hey Bill, Joe,

Clinitest isn't specific for glucose--it'll detect any reducing sugars (including 5 membered ones, I think). But not sucrose.

The problem with using a diabetic's meter to test RS is that it won't work. Depending on your yeasts, it can be the case that the yeast will eat all of the glucose and leave all the fructose. You can have (I've had it!) a wine with 1% fructose and NO glucose (had to feed it glucose to get it going again) which will test as absolutely dry with a diabetic's meter.

Dave, diabetic for 40 years now and wish>Joe Sallustio wrote "My reds almost always come up as 0.3 or .0.4 RS and

-- Dave

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Thanks for the info. Dave. Do you know if the remaining fructose can be fermented which would have an effect on the bottle pressure of a sparkling wine? If fructose is the end of the line the Glucometer still might be worth using to test for residule fermentable sugar.

Bill Frazier Olathe, Kansas USA

Hey Bill,

My understanding is that yeast CAN metabolize fructose, but prefer gluocse. My fermentation stuck at 1% fructose, and wouldn't go again until I added glucose.

But I don't know if you can count on that.

Dave

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I have had a really hard time running ripper on dark reds. Diluting with distilled water helps some. The best solution is to do the aspiration method or just send it to a lab.

You're probably measuring non-fermentable sugars. They typically fall in that range.

Tom S

Hi Joe,

I've had similar experiences with Clinitest on reds. My big reds have never read less than 0.3% RS by this method. Last year I was troubled by this and submitted a similar question to this NG. Search for 'Clinitest on dry reds' if interested in reading the responses but the consensus was similar to what I read here - non-fermentable sugars are detected by the assay.

I have not seen any publications that suggest anthocyanins affect the Clinitest but anthocyanins are often glycosylated. Is it unreasonable to think the sugar moiety has a role in inflating the results? I don't know.

I no longer worry about RS if it comes in at 0.3% as long as everything else looks and tastes right. I've tested several high end commercial California cabs and they, too, are often as high as 0.4%. The 2001 Plumpjack came in at 0.4% and that was a mighty fine wine!

RD

Fructose is fully metabolizable. The major metabolic pathway for sugar is called glycolysis. Normally an enzyme called glucokinase uses glucose into glucose 6 phosphate, which is then turned into fructose 6 phosphate.. There is another less specific enzyme (hexokinase) that can utilize several 6 carbon sugars, including fructose and make fructose 6 phosphate.

The problem with clintest I believe is that it tests for REDUCING sugars. That is it uses the reduction of copper to affect a color change. The problem with wine is that there are many things that can reduce the copper. Sulfite is a reducing agent for instance....so are the anthocyanins in red wine.

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Very interesting post Droopy. Thank you. Could you provide a reference for "anthocyanins being a reducing agent for copper?" Lum Del Mar, California, USA

I do not know of any specific research. I was speaking of more general chemistry knowledge (I use a copper reduction assay all the time to determine protein content in samples, and there are a lot of interfering substances).

I did look around and found an ACS article on standardized methods to determine levels of "antioxidant phenolics" which anthocyanins are. they describe a copper reduction assay in it.

I have not read it to determine if it is a probable problem in using the clintest with reds though....but to me at least it seems very liekly.

sorry for the double, but here is a very old article that has reference (page 6) to sulfites affecting the clinitest (Benedict's reagent) reaction.

Thanks much Droopy. Lum

Thanks all. I did try activated carbon on a sample prior to using clinitest, it has no effect at the level I used.

Joe