Results of Acid and SO2 testing of Must

[TNFISHRMAN]

I have a Batch of Concord Grape Scratch wine that I pitched the yeast in this morning. I had a couple of questions about the Acid Test and So2 test results, both of which were done after the sugar addition and before I had pitched the yeast. Just for info. sake the SG was 1.104 and Ph was 3.13 . The Vinoferm acid test showed 8.4 grams/ L. I cut the must 50/50 and used 4.2 ml of Indicator to give me a total of 8.4. Next I used the LD Carlson acid test kit andI came up with .65%. How do the two correlate are they anywhere close to the same results? I use a calibrated ph meter for indicating when I had reached a neutral point of 7 also.


The I tested the must for free SO2 with the vinoferm kit. I added a total of 20ml to get the color change. Which should have been 200 if I understand the kit correctly. I only added 6 campden tablets to 6 gallons of must. Could this be right??? Thanks for any help.

 

[Bert]

Some good questions there INFISHRMAN .And I don't have any answers, but did you run the tests more than once??? Some books say to run test more than once and look at an average. Unless one number is way out of wack.

 

[masta]

Not sure why you came up with such different results but testing acid by titration you should be using a pH of 8.2 for your end point. I would stick with the results from the LD Carlson acid test kit as this test seems to be the standard.


[url]http://www.finevinewines.com//Wiz/forum/forum_posts.asp?TID= 314&PN=1[/url]


Seeing the color change with the SO2 testing on a dark colored wine is difficult. A few things could have caused your high reading.


Not getting a good stir when testing....I do mine in a 50 ml beaker on a stir plate


If you just put the must together it takes some time before roughly half the added SO2 becomes bound to certain compounds in the juice.

 

[Joseph1]

Lynn,


The Vinoferm reading is 8.4 g/L, the L.D. Carlson reading of 0.65% is 6.5 g/L. Scott is correct in that if you are using the pH meter to determine the end point, 8.2 should be used rather than 7.0. This would result in more sodium hydroxide being added and the results of the two tests would be closer. Can't help with the Vinoferm SO2 tests.


There are a number of variables involved that can affect the results: freshness of buffer solutions to calibrate the pH meter and the freshness of the sodium hydroxide. Both have a limited shelf life.

 

[TNFISHRMAN]

Thanks for the replies, Lynn

 

[Hal Maulden]

Lynn,


I'm not familar with the Vinoferm kits but here is a couple of things to think about.


Anytime you use Iodine for any type of testing it should be kept in a dark bottle with zero light. And, it should be standardized very often. The weaker the solution the more it is vunerable to oxidation and light. I am working on sources to get a cheap(er) iodine, and a source for thiosulfate (used to standardize iodine). When I get these sources nailed down, I will work with Masta to post a workable procedure for SO2.


Acid - when you used the LD carlson kit, why did you not use the Phenolthalien(sp) indicator? It's much easier than a pH meter.





Hal

 

[bilbo-in-maine]

When I get these sources nailed down, I will work with Masta to
post a workable procedure for SO2.

Just speaking for myself, Hal, that's good to hear. You are right in saying
that the Accuvin test kit is expensive, even though it works well. If you
cook up a rig that is cheaper I'd like to hear about it.

Bill

 

[Waldo]

Me too

 

[peterCooper]

Is the problem one of calibrating or of inconsistent readings or differences
in procedure producing different results?

 

[Hal Maulden]

Peter,


Each procedure, just like any measuring equipment, has a level of error. Lot's of time this error is in the design quality, like a thermometer. Other times, its a combination of many things, including human error. In the case of SO2 it's a combination of: Chemical degradation, inherint error in the procedure itself, and the human error. If you look at any procedure or equipment, most of them give an accuracy at +/- some number. These ranges are also determined in a lab environment by a chemist or some trained professional under the best of situation. Therefore. sometimes the variation we see comes from the accuracy. Companies like Accuvin, has worked to take much of this error out by making the test simpler and less prone to error. In most cases this cost money to do.


I hope this answers your question.





Hal

 

[TNFISHRMAN]

I tried to reply the other day when I had more time and had just finished typing when the cable went out and I lost the post. I'll try to recap the answers to some of the questions that were mentioned and I have a couple.


The tests were repeated in some cases three times so I know the results of what I was getting was right. I also cut the must 50/50 for all the test with water to make seeing the color change easier.


I only used the PH meter with Vinoferm Acidometer kit. I didn't trust the litmus paper. The PH meter was Calibrated with fresh buffer solution 4 then 10 and checked at 7 everything was in calibration with the meter. I did use 7 for my neutraliazation point for the Vinoferm Acidometer. Was this right or should it have been 8.2 also?


I did use the phenolthaelin solution with the LD Carlson kit. Also, all indicating solutions are kept in the dark and were fresh. Some were less than a month old.


I am curious about where I cut the must 50/50 when I did the So2 test. How would this affect the outcome of the results?


Thanks for the help on this thus far. The batch is fermenting well and looks good so far. Lynn