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The Practice and Chemistry of Wine Making

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1 The Practice and Chemistry of Wine Making
Ron Bihovsky Chemical Consultants Network January 2017

2 Outline History of winemaking Grape cultivars Yeast strains
The winemaking process Chemistry of wine Fermentation of sugars to ethanol Acids Tannins Tastes (Aromas) – Good and bad Phenols Color of wine Tasting

3 History of Wine-Making
The earliest known evidence of wine comes from Georgia (Caucasus), where 8000-year-old wine jars were found. In the Bible, grapes are first mentioned when Noah grows them. “Noah, a man of the soil, planted a vineyard. He drank of the wine, got drunk, and he lay uncovered in his tent.” ויחל נח איש האדמה ויטע כרם וישת מן היין וישכר ויתגל בתוך אהלו (Genesis 9:20–21)

4 Yeast Ferments Sugars of Grapes to Ethanol
Saccharomyces cerevisiae (Yeast) 2 CH3CH2OH CO2 Glucose Ethanol Carbon Dioxide Fructose 700 different strains of Saccharomyces cerevisiae have been identified

5 Hundreds of Vitis vinifera grape varieties used for wine making
Grape Cultivars Hundreds of Vitis vinifera grape varieties used for wine making Cabernet Sauvignon Cabernet Franc Merlot Grenache Zinfandel Shiraz Petit Sirah Syrah Montepulciano Malbec Sangiovese Pinot Noir Barbera Valpolicella Concord: Vitis labrusca Sauvignon Blanc Riesling Chablis French Colombard Chardonnay Soave Gewurztraminer Pinot Grigio Muscat Chenin Blanc Catawba: V. labrusca + V. vinifera

6 Grapes Usually from California

7 Removing the Stems

8 Crushing the Grapes The Old-fashioned way

9 Yeast

10 You Don’t Want to Make Vinegar
Acetobacteraceae Sugars CH3CO2H + H2O O2 CH3CH2OH Acetic Acid (Vinegar) Prevent vinegar formation by Sterile Conditions Excluding oxygen Adding K2S2O5 (potassium metabisulfite) or KHSO3 (potassium bisulfite), sources of SO2 (sulfur dioxide), to kill wild yeast and bacteria. <350 ppm. Does not cause headaches.

11 Primary Fermentation

12 Wine Press Removes Skins and Seeds

13 Secondary Fermentation

14 Sediment Settling

15 Decant Wine From Sediment

16 Age in Oak Barrel or with Toasted Oak Chips

17 Decant Again and Bottle

18 Nasty Aromas (Faults)

19 Acids – Tart: pH ~ 3.5

20 Tannins – From Skin and Seeds
Astringent in red wine from grape seeds and skin

21 Phenols Slightly Bitter and Persistent

22 Color of Red Wine: Anthocyanins
Anthocyanins: Present in grape skins During aging, anthocyanins react with tannin and other molecules to form more complex molecules with red colors Which eventually become insoluble and precipitate

23 Pleasant Aromas (Flavors)

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