monitoring acids and ph in winemaking mike miller the reluctant chemist

Monitoring Acids and pH in Winemaking

Mike MillerThe Reluctant Chemist

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% 20%

Presence of acetaldehyde 5% 95% 100%

MLF in bottled wine 40% 60% 80%

Yeast Fermentation in bottled wine 50% 50% 100%

Presence of ethyl acetate 5% 95% 10%

Inadequate settling of white juice 80% 20% 100%

Presence of tyrene (T.C.A. = corkiness) 20% 80% 0%

Presence of 2,3-ethoxy-3,4-hexadiene (geranium) 5% 95% 90%

Presence of volatile acidity – acetic acid 80% 20% 80%

Presence of diacetyl 90% 10% 50%

Brettanomyces contamination 80% 20% 0%

Additive overuse (SO2, sorbate,etc.) 90% 10% 100%

When should I monitor?

• Harvest monitoring• Upon receipt• After primary fermentation• After malolactic fermentation• After any process• Periodically