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When to harvest: pH vs TA

In all of my research, everything tells me that to harvest grapes at a pH of > 3.5 is inviting spoilage or microbe growth. The recommended pH of a wine for reds is around 3.5. Microbes thrive in a pH > 4.0. And the optimum pH for bacterial multiplication is 4.2-4.5.

From the time grapes are harvested until they are wine, the pH is constantly influenced. Maceration/pressing will usually increase the pH .05-.2 units, because o fthe potassium contained in teh skins. Fermentation will increase pH around .1 units (for grapes). MLF you can expect .1 to .3 units of pH increase. Cold stabilization will also increase the pH (if the pH is > 3.5 to begin with).

So everything will do nothing but increase pH. The only way to reduce it is to add acid, mostly in the form of tartaric acid. For every .5 to 1g/l acid will drop the pH .1 units. So unless you are planning to add a substantial amount of acid, the pH will not move much down, but will continually move up.

That is why I have been picking my grapes at a much lower pH value and adjust for acidity.

Now, that said, I did receive a batch of grapes today from Roger in Salado. He donated 80 lbs of Cynthania grapes. These have a pH of 3.9, and the TA was .65 g/l. This is the highest pH I have worked with yet. The reason these grapes were harvested this way is to allow the maximum hang time possible before the grapes spoil.

What will be nice about this batch of grapes, is I can test the difference between grapes that are low pH but high acid, and a batch that are low acid but high pH and see which wine will taste better.

My best guess, is that in the short term, the pH 4.0 grapes will make a wine that will last 1-2 years in the bottle, but the pH 3.5 wine will outshine it after a few years in the cellar.

There is no doubt that the lower pH has a more vibrant color. But the high acidity might prove too much to overcome.

If you have any thoughts on this matter, please post them in the comments.

These were comments recovered before the crash:

Rick

Jeff, I picked about 175lbs of Norton this morning and crushed this afternoon. The TA came in at 1.1 (not nearly as high as last year). I’m wondering if the malo will drop it by the .4% needed? I have approximately 16 gallons of must and I am wanting to know how much if any calcium carbonate I would need to add in order to have a better chance of getting to the .7% target. Any help would be appreciated as a fellow Norton fan!

Jeff

My TA was exactly where yours is this year, it came in at 1.1. Malo from everything I can find about the subject, will lower that TA on average about .1 to .2. Sometimes more sometimes less.. sometimes a lot less. It all depends on the grapes. This is the first real Norton harvest I have had, and so I am at a very experimental stage right now. I’m just trying a few things and hoping for the best. I read that the CaCO3 should not be used to reduce the acid by more than .4.

This is what I used as a reference to lower my acidity (Taken from http://winemaking.jackkeller.net/acid.asp):

Calcium carbonate reacts preferentially with tartaric rather than malic acid, so one should not try to reduce acidity more than 0.3 to 0.4% through its use. A dose of 2.5 grams per gallon of wine lowers TA about 0.1%. After its use, the wine should be bulk aged at least 6 months to allow calcium malate, a byproduct of calcium carbonate use, to precipitate from the wine. The wine should then be cold stabilized to ensure tartrate crystals do not precipitate out after bottling.

Now, I was told to separate 25% of the wine into a separate container, and add ALL of the CaCO3 into that 1/4 container. Let it bubble, when it stops bubbling, add it back into the main container. This will let the calcium carbonate reduce the acid more evenly (tartaric, and malic) instead of reducing mostly tartaric. This is to help balancing later on (but since you are going to do a malo fermentation also, it might not matter). The measurements, are also must dependent, so you cannot always expect a .1 % drop for every 2.5g per gallon, but it is a good rough estimate. I added enough to reduce the acid by .2%, and it only lowered it by 1.8%.

Keep in mind too, that the malo will further reduce the acid, and also cold stabilization will further reduce the acid. By how much? I will let you know this winter.. :) At any rate, I chose to play it safe, and if I still need further acid reduction, I will add a little more in the spring. I am told that after fermentation, you can still use CaCO3 to reduce the acid, but they only recommend by .1% to avoid any off flavors (chalky, mineral) in the finished wine.

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