Re: checking acid levels

"Dar V" wrote "I was wondering what test kits you think are the best, and any other tidbits of helpful info would be greatly appreciated. Thanks in advance.

Darlene - I like the kit I use. Go to

and check out their Deluxe Acid Testing Kit. You might not need everything that comes with the kit so you can buy various components. Be sure to get the buret with the teflon stopcock...makes it easier to add single drops of NaOH solution as you get near the titration end point (I got cheap years ago and didn't get the stopcock...always regretted it).

You will need a pH meter to do proper acid titrations. I bought mine from Omega. A friend in our wine club just bought a meter from Morebeer.com.

Bill Frazier Olathe, Kansas

Dar,

I would agree with William using a pH meter. I bought a nice pH meter from a chemical supply house for $80. It reads to the hundredths place and accurate to .1. Plus you can measure the actual pH of the wine. Bonus. There is a procedure to follow for titrating when the pH meter goes to 8.2, it is the point where your NaOH used is the TA of your wine. Or if you will, the point where the color change takes place. I have a written procedure I will see if I can find and post it.

Lee

I currently use a pH meter to check my t.t.a. also. But the blue solution bottle says to take the reading when the pH = 7.0. I never questioned it because I thought that 7.0 was the neutral reading.

Should I be taking the reading at 8.2, and if so "Why"?

Thanks, Gus Calandrino

I used one of the cheapo kits you get at any wine supply for years. The work adequately with whites and adequately with reds with a pH meter. Last year I got one of the deluxe kits from PI and I love it. But you can certainly use one of the cheap kits if you are not sure about spending the extra money. Then when you get up to 10-15 batches a year totaling 90-100 gals., you might want to get more serious. (But you don't have to.)

Ray

are

Hi Gus,

You should indeed be titrating to a pH of around 8.2. This is because as you titrate your wine with NaOH you are creating salts of weak acids, namely Sodium Tartrate and Sodium Malate. These salts, since they were formed by the reaction of a weak acid and a strong base, are themselves weakly basic and provide a endpoint pH above 7.0, typically about 8.2. If you want to be more precise, you can make a plot of pH vs. mL NaOH as you titrate. The endpoint of the titration can be taken as the inflection point of the resulting curve. From my own experience, and countless others I assume, 8.2 is a pretty good number to shoot for.

CHEERS!

Aaron

The only real reason titration is done to pH 8.2 is that the conventional endpoint for titration is to look for color change using phenolphthalein as an indicator solution, which happens at pH 8.2. pH

7.0 would probably make more sense but TA is defined that way, at least in the US. As a purely practical matter, you probably won't observe a huge difference between using pH 7.0 and 8.2 as an endpoint; since pH is a logarithmic scale, it takes roughly 10x more NaOH to get you from pH 3 to 4 than it does from 4 to 5, ten times more from 4 to 5 than 5 to 6 and so forth. In other words, it will take the vast majority of the NaOH you add during titration to get you from pH 3.5 to 7.0 and a tiny amount to go from 7.0 to 8.2, probably not enough to significantly affect your titration result.

- Mark W.