Why test pH?

pH is most important for the following reasons:

- The lower the pH, the more stable the wine will be. At higher pH the wine is more at risk for microbial spoilage (bacteria and fungus have a harder time surviving in a more acidic environment).

- When adding sulphite, higher pH requires a higher amount in order to protect it.

I never test, but only because I don't have the equipment and don't want to shell out for it, but it is definitely a good idea to test if you have the means.

Also, if your pH gets to low your yeast will not grow.

When it hits the low 3's and fermentation will not start that is an indication that it is too low.

And remember that pH is a logarithmic scale. So a pH of 3 is 10 times more acidic than a pH of 4. Those 0.1 and 0.2 changes in pH can have a big effect.

Also, wine needs some acidity to taste right, otherwise its insipid -- like a glass of koolaid with a shot of vodka added.

I don't know about the low pH and having a hard time starting, I make mead and the pH is in the mid 2's. I would not call it a violent fermentation but it does go. Mead is wierd in regards to acid though, it gets much lower as it ferments. Maybe mine really are not that low initially and I never bothered to check. I will next batch though.

Joe

Well, you also have the case where some acids are stronger than others. You can have a fairly low TA and a low pH if the acids are fairly strong (malic acid has a pKa of 3.4, citric 3.1 and tartaric of 2.98, pKa is the pH when half of the acid is deprotonated so it is a measure of the acids strength)

Acetic acid has a pKa of 4.76. So the higher the pKa the stronger the acid is, because more of the H ions will be in solution at that pH. It is kind of hard to get your mind around. It is kind of opposite of what you would think.

But the thing is, the total amount of acid put into the must also affects yeast activity. You can get a low pH with a small amount of somethign like malic acid. Which is common in meads (low tartaric acid content as opposed to wines).

Another reason that pH affects yeast activity is that it disrupts their metabolic rate (it is hard to do the chemical reactions if the pH is not just right). But that does not mean that it will not go on at all.

"Acetic acid has a pKa of 4.76. So the higher the pKa the stronger the

acid is, because more of the H ions will be in solution at that pH. It

is kind of hard to get your mind around. It is kind of opposite of what you would think. "

Ok, so I got that backwards. The lower the pKa the stronger the acid. It has been a while since i had my organic and biochem. Maybe I have been drinking too much homemade wine.

pH is one of those finer points of making wine that an armature can ignore but an advanced armature may become evangelistic about. If you are primarily making wine that will be drunk up in 2 years, you can generally avoid the issue.

If you want to lay down some wines for 5 or 10 years, pH can be very important and you should consider learning about it and putting out the $100+ for a good tester.

Ray