1. Introduction to Winemaking: Part 4. Secondary Fermentation Dr. James Harbertson Extension Enologist Washington State University

2. Secondary fermentation is conversion of malic acid to lactic acid and CO 2 C 4 H 6 O 5  C 3 H 6 O 3 + CO 2 Lactic Acid metabolizing bacteria are responsible for fermentation Deacidification: decrease in titratable acidity and increase in pH Wine stabilization and flavor change Secondary Fermentation

3. Deacidification I Acidity due to malic acid is reduced by 1/2 Lactic acid is less acidic than malic by loss of one functional acid group This relationship is not always the case:  RS converted to lactic acid by yeast  Loss of potassium bitartrate by ppt.  Malic acid catabolized by yeast

4. Deacidification II pH increase is not easy to predict It depends on buffering capacity of wine IE the [organic acid] and starting pH Lactic acid is weaker acid than malic acid The greatest pH change you should see is about 0.2 units. In wines with a pH<3.4 the increase will only be about 0.1 units. Although this is still a desirable change in sourness generally speaking! Color of wine will decrease slightly because of anthocyanin coloration is greater at low pH.

5. Re-acidulation Sometimes it is necessary to add acid back to adjust TA to acceptable value Don’t add citric acid because ML bugs will convert it into diacetyl (butter aroma) (Movie time!) Tartaric acid is acid of choice for all acid additions Although it is expensive and some losses due to potassium salt precipitates occur

6. Wine Stabilization Wine is stable to further infections by other ML bacteria and more stable to other infections ML strains will use up most of the resources left after yeast is finished Best to inoculate with ML strain and not depend on “native ML” for control Best to do primary and secondary ferments separate because they can inhibit each other

7. Flavor Change Less Sour!! Diacetyl is formed during secondary ferment Aroma is described mostly in terms related to butter aroma  I.E. Rancid butter, butterscotch, cream Aroma change more evident in white wines than red wines Diacetyl is formed from citrate and pyruvate

8. Wine Style and ML Red Wines:  Happens in most but usually does not change wine style that much  Done primarily to stabilize wine White Wines:  More infrequent because whites are dominated by grape aromas, and flavors  In barrel fermented wines where other aromas are present it is more acceptable  Strains available that don’t make as much butter aroma so it’s use for deacidification is more prominent

9. Wine Style and ML II Vinhos verdes “Green wine” Minho region of Portugal Lack of ripeness in grapes, not color of wine High Malic acid from viticultural practices coupled with no ML in winery led to bottled wine that was fizzy Consumers loved it However it was cloudy and sold in opaque ceramic bottles Now the wines undergo ML and you can’t get a true vinho verdes

10. Controlling ML Yeast Bacteria Interaction Stimulation for wines pH  3.3 Inhibition for wines pH  3.3 Detection Cultivation

11. Yeast Bacteria Interaction Yeast and bacteria are competing for nutrients Yeast can both inhibit and stimulate bacterial growth EtOH, bisulfite and fatty acid formation by yeast inhibits bacterial growth SO 2 binding and the products of yeast autolysis after sur lies aging stimulate bacterial growth Bacteria can stimulate death phase in yeast Easiest to inoculate wine with ML strain after primary fermentation has occurred for simplicity

12. Stimulating ML fermentation Don’t add SO 2 Temperature  Maintain temperature above 18  C Acidity  When pH needs to be raised chemical deacidifications can stimulate growth Ethanol  Bacteria are inhibited at around 14% EtOH

13. Stimulating ML II Macronutrients and Micronutrients  Amino acids and five carbon sugars  Some inoculums have many of the necessary components present  Wine is to be stabilized by ML fermentation so does not make sense to add nutrients which may encourage growth of spoilage organisms Oxygen  Bacteria like small amounts of oxygen but in practice anaerobic wine conditions work fine

14. Inhibition Add SO 2  0.8 mg/L molecular pH adjusted Temperature  Below 18  C and as low as 13  C High EtOH does not always inhibit because often coupled with high pH Acidity  Adding tartaric acid will help but may not stop it  Wines pH 3.3 and below need to be stimulated while wines pH’s above this it will be difficult to stop

15. Inhibition II Elimination of viable bacteria  Don’t blend wines with differing ML status Sterile filtration and sterile bottling  Like yeast will be filtered out with pore sizes no larger than 0.45 microns  Sterilize bottling equipment with heat Chemical inhibitors  Velcorin (dimethyl decarbonate) will work with SO 2 and low pH  Fumaric acid final concentration (0.5 mg/L) is needed but low solubility limits its use

16. Detecting ML Measuring malic acid disappearance is best pH and TA increases can arise from other phenomenon Increase in turbidity and effervescence (not measurable) Determination of malic acid can be achieved with paper chromatography or enzymatic analysis Enzyme kits are fast but expensive and require a spectrophotometer Paper chromatography requires a fume hood and is time consuming

17. Cultivation Specific strains with desirable characteristics can be purchased They are generally grown in complex media containing growth factors and a yeast inhibitor Companies that sell yeast also sell ML strains Wines & Vines guide is directory contains info WSU Dr. Edwards works in this area and is an excellent contact for technical difficulties