Does wine acidity change during aging

Wine acidity does not change much during aging, if at all (minor fluctuations might occur of +/- .05 pH). The only other factor during aging that could affect acidity would be a spoilage organism leading to excessive Volatile Acidity and acetic acid production (e.g. the wine turning to vinegar).

However, it is important to note that the perception of acidity of a wine can change as it ages because astringency (e.g. tannins) and acidity have a tendency to amplify each other in terms of perceived acidity/astringency. Therefore, higher tannins can make a wine taste more acidic (or vice-versa). As the wine ages and tannins soften, complex, and eventually precipitate out of a wine, the perceived acidity might become lower and leading the wine to taste 'softer'.

While cold stabilization can have an affect on wine TA / pH, it is usually quite minimal unless the wine is very high or low in TA / pH. Common professional practice with overly acidic wine is to adjust pH with KHCO3 (Potassium bicarbonate). However, this is only good for minor adjustments. Too much KHCO3 can lead to a wine tasting soapy or even salty.

There are actually two things about the grapes. They can taste unripe (a green taste), and they can taste ripe but won't be sweet yet. I made several wines from my own grown and harvested grapes.

If you make wine from grapes which still taste unripe, you will get this taste in your wine. If you make wine from ripe, but not yet completely sweet grapes, you can make a nice wine from them.

The acidity comes from the cream of tartar acids. If you cold stabilize your wine, these will drop out of solution and the taste will improve. Take a month or six before you bottle them.

There are of course other tricks to deacidify wine, but I haven't used them. I haven't even measured the acidity with 'blue lye' (?) (sorry don't know the translation). Just press my grapes, ferment, rack into DJ's and keep a month or six in a cold place before bottling them.