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The Chemistry of Winemaking April 9, 2013 Debbie Knutzon, Synapse Wines

The Chemistry of Winemaking April 9, 2013 Debbie Knutzon, Synapse Wines. Basic Wine Chemistry Analyses. pH Titratable Acidity Free and Total SO 2 Volatile Acidity % Alcohol Malolactic Fermentation Assessment. pH -log [H + ]. Normal levels in wine white: 3.1 – 3.6 red: 3.3 - 3.9.

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The Chemistry of Winemaking April 9, 2013 Debbie Knutzon, Synapse Wines

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  1. The Chemistry of WinemakingApril 9, 2013Debbie Knutzon, Synapse Wines

  2. Basic Wine Chemistry Analyses • pH • Titratable Acidity • Free and Total SO2 • Volatile Acidity • % Alcohol • Malolactic Fermentation Assessment

  3. pH-log [H+]

  4. Normal levels in winewhite: 3.1 – 3.6red: 3.3 - 3.9

  5. Why measure pH? • pH affects: • Effectiveness of SO2 • Rate of browning • Microbiological growth • Related to TA but not directly • Effect on color

  6. Titratable Acidity (TA) • Measurement is an acid-base titration that represents the total amount of available protons from all the acids in the wine • Expressed as grams tartaric acid per 100 ml (or per liter) • Not a direct correlation with pH due to buffering capacity of the grape/wine

  7. TA • TA has a big impact on flavor /perception of wine • “Typical” range: 5-8 g/L • Higher end: wine tastes sharp or tart but will age more gracefully • Lower end: wine tastes dull, flabby and will not age well

  8. Measuring TA • Titrate a known amount of wine (degassed) with 0.1N NaOH to a known endpoint. By measuring the amount of base (NaOH) added, the amount of acidity in starting wine can be calculated. • Phenolphthalein vs. pH meter

  9. Sulfur Dioxide (SO2) Uses: • Prevent chemical and enzymatic oxidation • Protect against microbial spoilage • Functionality derives only from free forms

  10. Sulfur Dioxide (SO2) • Total vs. Free SO2

  11. Free SO2 exists as either molecular or bisulfite Uses: • Prevent chemical and enzymatic oxidation • bisulfite • Protect against microbial spoilage • molecular

  12. Amount of SO2 in molecular form depends on the pH of wine

  13. minimum ppm free SO2 pH 0.8 molecular 0.5 molecular 3.0 13 ppm 8 ppm 3.5 40 ppm 25 ppm 3.8 79 ppm 49 ppm 4.0 125 ppm 78 ppm

  14. Measurement of SO2 Ripper Aeration-Oxidation Free or total yes yes Relative ease easy medium Cost less more Ease of end-point white easy easy red hard easy

  15. Addition of SO2 Potassium metabisulfite (KMBS) • KMBS contains only 57% sulfur dioxide, so need a correction factor of 1.75 • can find online calculators or printable tables

  16. Volatile Acidity (VA) • Indicator of microbial spoilage (acetic acid) • Acetic acid produced by Acetobacter (duh!) • Conversion of both glucose and ethanol • Lactic acid bacteria can convert glucose to acetic • Brettanomyces can produce acetic acid Prevention: SO2 and no head space

  17. VA measured by steam distillation

  18. % Alcohol • Ebulliometer • simple and accurate • Based on ethanol’s depression of boiling point

  19. Malolactic Fermentation • Bacterial fermentation that converts malic acid to lactic acid • Generally a qualitative determination using paper chromatography to follow the depletion of malic acid from a sample • Useful for determining when to add KMBS at cessation of fermentation

  20. “Old-School” References The Complete Handbook of Winemaking The American Wine Society published by GW Kent Knowing and Making Wine Emile Paynaud John Wiley & Sons Winery Technology & Operations Dr. YairMargalit Wine Appreciation Guild

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