Monitoring Acids and pH in Winemaking Mike Miller The Reluctant Chemist

5.0 g H2SO4/L = 7.5 g tartaric acid/L TA Conversions % TA to g/L: multiply by 10 0.7 % TA = 7 g/L meq/L to g/L: divide by 13.33 100 meq/L = 7.5 g/L g H2SO4/L to g tartaric/L: multiply by 1.5 5.0 g H2SO4/L = 7.5 g tartaric acid/L

Why are pH and TA important? pH ~ sourness pH and TA ~ astringency High pH = less red, more brown High pH = reduced capacity to mature High pH = more ionized components, more oxidation High pH = poor bentonite fining; greater protein instability High pH = greater susceptibility of bacterial growth pH + TA balance sugar + alcohol + glycerol

The major winemaking acids Tartaric Malic Citric L-Lactic Succinic

What are the optimum levels? pH: red @ 3.3 – 3.6 white @ 3.1 – 3.4 TA: red @ 6 – 8 g/L white @ 7 – 9 g/L

How can I increase TA levels? Add tartaric acid Add DL-malic acid Add L-malic acid Add L-lactic acid Add citric acid Add fumaric acid Add sorbic acid

How can I decrease acidity levels? Maloalcoholic fermentation Deacidify with calcium carbonate Deacidify with potassium bicarbonate Treat with Acidex (takes two steps) Conduct MLF Blend Stabilize Ameliorate

How do I adjust pH? Ion exchange Sulfuric acid?

What about those acids I don’t want? D-Lactic acid Acetic acid

And that other acid? Sulfurous acid, a.k.a. SO2

SO2 Chemistry SO2 + H2O = HSO3-1 + H+

How can I best control pH, Acids, and Acidity? Monitor

Wine and winemaking problems Name of Problem Flaw Fault Caused by faulty Winemaking Presence of reduced sulfur compounds (e.g., H2S) 20% 80% Presence of acetaldehyde 5% 95% 100% MLF in bottled wine 40% 60% Yeast Fermentation in bottled wine 50% Presence of ethyl acetate 10% Inadequate settling of white juice Presence of tyrene (T.C.A. = corkiness) 0% Presence of 2,3-ethoxy-3,4-hexadiene (geranium) 90% Presence of volatile acidity – acetic acid Presence of diacetyl Brettanomyces contamination Additive overuse (SO2, sorbate,etc.)

When should I monitor? Harvest monitoring Upon receipt After primary fermentation After malolactic fermentation After any process Periodically