First question, why do we add acid?
To achieve balance in a wine where tannin, alcohol, and, flavour are in harmony. The amount of acid can be too high making the wine sour or too low giving it a flat, lifeless mouthfeel.
Higher acids to tend to make fruit appear fresher and colour brighter. For the wine geek, you can check out the chemistry behind this in the video in the article “Just How Does Sulphur Affect Wine? + A Pro Tip for Buying Old Wine”.
The amount of acid in the wine is related to the pH, however, many chemicals in the wine impact (buffer) how direct that relationship is.
The pH impacts microbial stability, a low pH creates a less friendly environment for bad bugs to grow. It also makes any Sulphur added more effective and able to kill bugs.
Technically, many winemakers target a pH of less than 3.65 in a finished red wine.
That covers balance and microbial stability.
What about the ability to age and stay fresh?
Well, the lower the pH and the higher the acid the fresher the wine will stay.
To answer your Barossa question acid will be added to most wines.
The article referred to above explores this in detail with a white wine experiment I conducted over 20 years with wine bottled at 2 different Sulphur levels.
Typically warmer climates need to addmore acid than cooler climates, some cooler climates need acid removed!
Within a region, different vineyards as a result of their management, vine age, wine balance, yield, will give different pH and acid profiles.
Older vines with lower yields and better balance generally have better pH and acid profiles.
If a vineyard has been loaded with potassium this can dramatically reduce acid levels in a wine as the potassium will encourage the formation of crystals with tartaric acid that will then fall out of solution.
As a winemaker, you then have to decide what type and more importantly when to add acid. In Australia, there are a number of different acids that can be legally added to wine.
For reds it’s normal to add tartaric acid.
For whites it’s common to use tartaric acid, and, less so to use citric acid, lactic acid and malic acid.
The trick is to know the style of wine you want to make and get everything under control early. There is a fair range of pH and acid levels that will be technically correct giving you room to move.
Wine is a chemical soup that changes dramatically during fermentation, the longer you wait the harder it is to get it under control as the multiple chemical equilibriums start to move against you.
So in general, if needed, I’d hit it hard and early. The earlier you sort it, the better the integration of the acid, and, end texture of the wine. If you add a large amount of acid late in the winemaking process, that acid will not integrate as well, and, will give the acid a hard texture in your mouth.
Hope that helps! Short, but, very complicated question!
Making wine with real personality and intrigue, wine that says DRINK ME, is not easy. Understanding the ‘rules’, and, having the numbers from the lab, allows you to break them, and, push the boundaries, with the confidence that you’re less likely to bugger it up. The greatest sin a wine can make is to be boring!
There are too many acids in wine to cover them all here. Some are present in the grapes and juice, others are produced by yeast or bacteria, some are converted from one acid to another by bugs.
Finally, there are heaps that can be legally added, all of them have different perceived intensity and impacts on aroma and flavour as well as well as strength ie the ability to change the pH of the wine.