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Can you explain the terms "residual sugar," "brix," "total acidity" and "pH" as they relate to wine?

Can you explain the terms "residual sugar," "brix," "total acidity" and "pH" as they relate to wine?

"Paul, I joined the club to learn about wines and enjoy thoroughly the wines you have sent. The information is great and educational and I like the way it leans toward the humanist side rather than the technical side. Some of the bottles you have sent to me, however, list interesting information of which I don't understand. Please explain. Residual sugar, Brix, Total acidity, pH, Alcohol."
– T.R., Laguna Beach, CA

Thank-you very much for your supportive comments and enthusiasm! Yes, we do tend to stay away from technical jargon, as it can be quite confusing at times. But in the interest of clearing up these matters for you, we'll define some of the terms commonly found on wine labels.

Residual Sugar (often abbreviated "R.S.") is the amount of natural grape sugar remaining in the wine at the end of fermentation (the process, which is conducted by yeast, of converting sugar into alcohol). 1% R.S. is barely perceptible to most people, while 2.5% to 4% tastes fairly fruity. A wine containing 6% R.S. and above is a sweet wine.

Brix (pronounced "bricks") is a term describing the percentage of sugar in the grape juice at the time of harvest. A high Brix (well above 20 degrees) yields a wine, depending upon when fermentation ceases, which will be either high in alcohol content or high in residual sugar. If fermentation is stopped before all the grape sugar has been converted into alcohol, there will be a certain degree of residual sugar, as above, with low to moderate alcohol content in the finished wine. If the wine ferments out dry, the alcohol will be higher, with but a trace of residual sugar.

Total Acidity describes the amount of fruit acids remaining in the wine after the vinification (the wine-making process). A wine with low acidity will taste "flat" whereas one with too high an acid level will be unpleasantly tart. Acceptable levels are generally from about .6% to just over 1%. Proper acid content not only gives the wine its "zing", but also figures majorly in its ageing potential.

pH also refers to the wine's acidity. Some acids are simply more acidic than others. Water with a completely neutral acidity rates a 7 on the pH scale. The lower the pH rating, the higher the acidic character of the substance in question. Wines generally run in the 3.20 to 3.70 range. Wines with a high pH (low acid) are more subject to spoilage and generally will not age as well as those with a low pH (high acid). A wine lacking in acid will taste dull.

Alcohol (stated as a percentage of the wine's volume) spans from 7% - 10% (German wines), to 11% - 13.5% (table wines), to 17% - 20% (fortified wines). Sound wines contain the above elements in proper balance with each other. That can easily be discovered in the lab, but the bottom line is, "Hey, how does it taste?"