Testing for total acidity

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Testing for total acidity

Postby 2007Shelby » Thu May 31, 2007 1:03 pm

Hi,

New to the forum, so I apologize if I am bringing up a topic that's been addressed before.

Anyway, I have a small backyard vineyard on the east coast, and am looking for a more accurate way to test for total acidity. I've found this to be a problem not only with reds, but just a general PITA when approaching harvest, trying to track acidity in making a harvest decision.

I've been looking at two products offered by More Wine!...the first one is the MT150: Advanced Titration Kit for Total Acidity, and the MT682: Automatic Total Acidity Titrator. Obviously one is much more expensive than the other, but taking cost out of the equation, does anyone have experience with either of these pieces of equipment, and if so, care to share an opinion?

My main question is how much of a sample does either unit require to conduct the test? Are we talking a few ML, or something appreciably larger?

Any help or opinions would be greatly appreciated!

Thx,

Ron
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Postby tristan » Mon Jun 04, 2007 2:38 pm

Ron - Here is the basic breakdown between the two products:

The MT150 is basically just an easier, more accurate way of delivering the Sodium Hydroxide (NaOH) used in a standard Acid Test Kit to neuralize the acid in the grape and determine how much was there. This item replaces the syringe included in the Acid Test Kit with self-zeroing buret. The testing procedure itself remains the same - add the NaOH to your 5mL wine sample until the correct color change or pH change is observed. You can make a standard acid test much easier and more accurate simply by using a pH meter to determine the endpoint of the test rather than trying to judge it by a color change. This is especially true for red wines. You can check out this paper for more information about acid testing with a standard Acid Test Kit.

The MT682 Hanna Titrator is a great machine and is very fast to work with. It basically operates on the same testing protocol that the basic Acid Test Kit works on, determining the endpoint of the test based on pH. Instead of you looking at a syringe or a buret to determine how much NaOH reagent was necessary to neutralize the acid in your sample, the machine calculates how much was used based on the flow rate of the built-in pump. Overall, the machine is very easy to use and very accurate - great for somebody with no science background or with some misgivings about their ability with the standard testing method. Whether or not this is worth $600 to you is really a value judgement for you to make, not something that we can determine for you.

So here's a little blow by blow for the two systems:

MT150 / Standard Acid Test Kit
    5mL wine sample
    Approx 5-10min per test
    Approx $0.50 reagent cost per test
MT682 Hanna Titrator
    2mL wine sample
    Approx 2-3min per test
    Approx $1.50 reagent cost per test

Hope this helps!
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Postby StuBrew » Mon Jun 11, 2007 8:50 pm

I realize I'm coming to this topic late, but here is my $0.02

For harvest decisions, I would rely on taste first and brix second. Unless you are making commercial wine in a place like Oregon which forbids acid addition, any acid deficiency can be made post-harvest. Chew the skins, look at the seeds (then chew them), and decide if you like the flavors and if they are developing in the right direction. Once you like the flavors/tannins, pick the grapes and adjust the acidity later.

When you decide to adjust the acidity, make a few additions at increasing levels to a small sample and decide which level tastes best, then add that level. Disregard the TA. If you have the ability to measure the pH, try to addjust to the lowest pH that tastes "balanced", assuming ML has finished (ML struggles at pH < 3.8 unless you've got some fancy strain like Chr Hansen CH 35 which takes low pHs.)

The tartness of a wine is related to the TA, but also is affected by the RS, alcohol and buffering factors (K+ primarily.) Most importantly, there is not one right or wrong TA, just what tastes right. I hate to see money spent on useless analysis that could buy a few nice bottles of wine or beer.
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