Introduction to Winemaking Part 3: Fermentation Dr. James Harbertson Extension Enologist Washington State University

Primary fermentation is conversion of sugar into EtOH and CO 2 is carried out under anaerobic conditions. Anaerobic: Lacking oxygen C 6 H 12 O 6  2CH 3 CH 2 OH + 2CO 2 Heat is a by-product of reaction Yeast can be killed if temperature gets too high. Above 38  C problems occur. Fermentation temperature can be regulated CO 2 is dangerous by-product that needs to be managed Fermentation

Fermentation Temperature Whites generally ferment at a lower temperature than reds. White fermentation temperatures  Lower temp. to preserve volatile components Red fermentation temperatures  Higher temp. for extracting phenolic components from skins and seeds

Regulation of Fermentation Temperature Metal tanks (excellent conductor) can use jacket filled with coolant (ethylene glycol, ammonia) Wooden tanks (poor conductor) can use heat exchangers (uses tubes filled with cooler liquid, that when moved past warmer liquid trades temperatures). Requires external pump. Barrel fermentation temperature not controlled

Jacketed Tank

CO 2 Management Carbon dioxide is dangerous by-product How much is produced?  About 3 times the volume of liquid during one day of a slow fermentation. Fermentation rooms must have proper ventilation Cellar workers going into tanks should work in pairs CO 2 detectors should be used in winery (Workplace safety have an upper limit of 0.5%) Evolved CO 2 also will remove off odors and pleasant ones.

CO 2 Management II Tank fermentations  Ventilation system with a fan or blower  Ferment in an outside tank Barrel fermentations-Inside  Ventilation system required  Air conditioning load to cool room is greatly effected by outside air.  About 10,000 liters of CO 2 produced by one complete barrel fermentation.

Example You have a 10,000 gallon tank of 24 Brix. How much CO 2 will it make in one day if it produces 56 L CO 2 /L of juice fermenting at 1 Brix per day at 20  C? How much for an entire fermentation? (56 L CO 2 /(L of 1 Brix per day) *(37,854.1 L/10,000 gallon tank)= 2,119,824 L of CO 2 ~ 2.2 million liters of CO 2 (2,119,824 CO 2 /Brix) *24 Brix= 50,875,776 L of CO 2 51 million Liters of CO 2 will be produced in total!!!

Ventilation System

Yeast Selection Basic Criteria for selecting a yeast Fermentation vigor (rate of fermentation) Finishes fermentation to dryness Reproducible fermentation characteristics Ethanol tolerance Temperature tolerance Produces no off-flavors or aromas Sulfur dioxide tolerance

Yeast Selection II Dried yeast are produced healthy under aerobic conditions with plenty of survival factors (saturated fatty acids, sterols)  Healthy cell membrane for EtOH tolerance. Dried packets will survive for one year if stored in cold. Before addition to must, re-hydrate in a small volume of warm (40  C) water. Add about g dry per L of must.

Yeast by-products Aside from EtOH and CO 2 Glycerol-viscous by-product  Not enough to modify wine mouth feel  Elevated production in  SO 2 conditions Acetic Acid-vinegar (volatile acid)  Normal production (100 to 200 mg/L) can be made from nutrient deficient musts  Also made by spoilage organisms (Acetobacter)

Yeast by-products II Higher Alcohols- higher MW higher BP Formation by breakdown of amino acids (removal of amino group at end of pathway). Excess amino acids does Also made from sugar breakdown Not enough to normally change aroma of wine.  Isoamyl alcohol (banana)  Active amyl alcohol (?)  N-propyl alcohol  Phenyl ethanol (rose aroma)

Yeast Selection III Don’t choose a yeast because it supposedly produces different aromas CO 2 blows of most yeast volatiles during fermentation. “Fermentation bouquet” are unstable volatiles that can be achieved through cool fermentation and protected from air contact it can be maintained for about a week. Research showed no detectable differences between strains with same initial juice after fermentation was complete. During fermentation all lots of odors are detected but not after fermentation is complete. Only exceptions to this are wild yeasts and different species of Saccharomyces

Wild Yeasts Examples: Kloeckera, Hansenula, Candida, Brettanomyces, Zygosaccharomyces Can produce off aromas (horse sweat, feces) Compete with Saccharomyces Generally are SO 2 and EtOH intolerant. Can be reduced by early SO 2 addition and inoculation with Saccharomyces. Are temperature intolerant, at 25  C they are inhibited while Saccharomyces will survive up to 38  C

Stuck Fermentations Two classes: Stuck and Stinky Some can be easily fixed, while others are more challenging. Causes: EtOH toxicity, nutrient limitations, substrate inhibition, toxic substances and temperature shock. Monitoring Fermentation is key to catching a stuck or sluggish ferment.

Stuck II Ethanol toxicity is common Cell membrane permeability is damaged Acidity inside cell  putting a load on membrane bound enzymes required to remove it. Making more fatty acids to fix membrane requires O 2 Oxygen introduction (aeration) at beginning and at end of fermentation through stirring has been shown to these types of problems. A more ethanol tolerant Saccharomyces strain or species can also be used from the outset or brought in to finish the fermentation.

Stuck Fermentations I Nutrient deficiency most common problem Nitrogen or phosphate deficiencies In some cases it is vitamin related Yeast strains display different sensitivities to nitrogen limitation. Nitrogen and phosphate can be added in form of diammonium phosphate (DAP) to adjust for deficiencies. 0.5 g/L usable nitrogen necessary for max yeast biomass and 0.2 g/L nitrogen for dryness.

Stuck Fermentations II Stinky ferments (skunky, rotten eggs, garlic) Generally H 2 S, CH 3 SCH 3 CH 3 SSCH 3, CH 3 CH 2 SH Threshold µg/L range Unknown cause Linked to vitamin deficiency, elemental sulfur left on berries, free amino nitrogen deficiency, metal ions and perhaps sulfite. Copper sulfate can be used to remove H 2 S (less than 0.5 mg/L may be added with 0.5 mg/L residual US 0.2 mg/L other countries.

Copper Sheet

Restarting A Fermentation Start with fresh media and yeast Add in portion of the stuck ferment Allow for vigorous fermentation (adaptation) Add in stepwise fashion portions of stuck ferment Early diagnosis is key because it is more difficult to start stuck ferments that have gone full into full arrest. Plotting Brix depletion curve will show problem ferments.