Titratable Acidity: A Better Way?

A man, his contraption, and a different way

I learned of a different way to test for titratable acidity, the other day. At the last meeting of the Puget Sound Amatuer Wine and Beer Makers club, Don Proctor demonstrated this method using an odd looking device. He used ordinary baking soda (sodium bicarbonate) to neutralize the acid in a test sample. The important thing about this chemical reaction is that it gives off carbon dioxide (CO2) in direct proportion to the amount of acid neutralized. Now his device didn’t look so odd. The stoppers, tubing, glass cylinders, and green liquid were used to measure the amount of CO2, and if you know how much wine was in your sample and how much CO2 was produced, you can find the acidity of your sample.

The difference is in what you measure

This method, and conventional titration, both aim to measure the amount of acid by neutralizing it with a base. In a titration, you add a carefully measured amount of base until all the acid is neutralized. It’s important that you add just enough base to neutralize all the acid – no more and no less – because you determine the amount of acid in the sample from the amount of base that you add. Because you have to measure the base so precisely, it’s best to add it in liquid form. That means you need to have a solution of base at a precise concentration. Now, this is easy to find, but it’s expensive and it has a short shelf life.

Why the new way is better

You need to neutralize all the acid in Mr Proctor’s method too, but you don’t need to know how much base it took to do that. That means you don’t need to determine the end point (no pH meter) and you can use cheap, shelf stable baking soda instead of expensive perishable sodium hydroxide. That’s a big plus, as I found out the last time I ran out of chemicals. I’m going to have to get one of these contraptions!

Update 9/8/2008: A picture is worth a thousand words

If you’re having trouble visualizing it, take a look at this photo.

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