Introduction to Winemaking Part 2: Must Additions Dr. James Harbertson Extension Enologist Washington State University

Must Additions Must is the crushed fruit. Sugar Water Acid Sulfur Dioxide Yeast Inoculation and Nutrients Other additions..

Sugar Additions Sugar additions are allowed in WA  Concentrate or pure sugar, or other fruit  Additions cannot change final Brix past 25. Can be added after fermentation or before Process is known as chaptalization, after the French man who popularized it, Jean-Antoine Chaptal. Regulated in most countries Illegal in CA and Oregon. Legal in some AOC’s in France.

Water Additions Water may also be added to dilute juice to a minimum of 22 Brix This can be done in the form of fermentation facilitation, or equipment flushing Can be done pre or post-fermentation. Primarily done to lower eventual EtOH concentration. Reverse osmosis used to reduce EtOH but very costly. Better to not make mistake at the outset.

Acid additions In practice it is done to reduce the pH and increase the titratable acidity. Tartaric acid and malic acid may be added to fermenting juice. Tartaric is the best choice because it is microbial stable. For reds done early about a day after skin contact because of high potassium content of skin.

Acid Additions II The magnitude of change from the addition is determined by the buffering capacity of the must. The increase in TA will be due the difference in the magnitude of the addition and the loss of K2TAR. The pH change will also be dependent upon the buffering capacity of the must. In practice additional acid is used to achieve a targeted value. Acid of known concentration is added to a representative sample and monitored on a pH meter.

Sulfur Dioxide Inhibits and kills native yeast and bacteria Inhibits oxidative enzymes that cause browning Decolorizes anthocyanin pigment Interacts with phenols in the competitive oxidation Delays non-enzymatic browning

Chemistry of Sulfur Dioxide SO 2  HSO 3 - pK a = 1.86 SO 2 known as the molecular form HSO 3 - known as the bisulfite form Each form reacts differently based on its own specific chemistry.

Molecular Form Functions Inhibits oxidative enzymes  Behaves as competitive inhibitor Kills wild yeast and bacteria Effective hydrogen peroxide trapping agent. Is volatile and detectable by sensory  Pungent metallic odor Is lost due to its volatility

How much is necessary? From 25 mg/L to 75 mg/L SO 2 required to inhibit from 75 to 97% of PPO enzyme. Laccase a more potent oxidative enzyme found in Botryized fruit requires 150 mg/L (too much) mg/L molecular SO 2 is necessary to reduce viable cell population by an order of magnitude (10X). Assumed that addition for enzyme reduces microflora significantly enough if you are inoculating

Free SO 2 to achieve necessary molecular For wines pH about mg/L free SO 2 necessary for mg/L molecular. Equation can be used for specific cases. Just plug in your pH to equation and the free SO2 will be calculated.

Bisulfite Functions Decolorizes anthocyanin by binding them  Disrupts conjugated system Is easily covalently bound by acetaldehyde, keto-acids and sugars. Bound form disrupts normal equilibrium. Establishes new equilibrium of bound and free. Makes estimation of sulfur dioxide difficult. Forces methodologies to measure bound and free sulfur dioxide. Current methodologies have problems estimating bound and free form because of differential disassociation constants of bound forms.

Yeast and Yeast Nutrients Grape juice fermentations are done by a strain of Saccharomyces cerevisiae. They can happen naturally (native yeast that live in the winery), or by inoculation with a commercial strain. Use of sulfur dioxide and inoculation generally minimize the influence of wild yeast(s) on wine quality.

Yeast and Yeast Nutrients II Inoculation can occur any time after crushing but is usually done after other additions are complete. Yeast nutrients are generally included in the inoculation step as a safeguard for stuck fermentations. Yeast nutrients include ammonium salts, amino acids and vitamins. Not all musts require nutrients but it is easier and cheaper for smaller wineries than having to analyze everything.

Other Additions…. Enzyme Additions Tannin Additions

Enzyme Additions Direct additions (not on fixed bed) Sensitive to temperature, EtOH and SO 2  Pectinase-Juice yield enhancement enzymes Also helps prevent hazes in wines  Glucosidase-Freeing bound volatile compounds Muscat, Riesling, Gewurtz. contain bound terpenes that can be freed to enhance aroma by using enzyme  Glucanase-Break down colloids that foul filter Botrytis infected grapes contain colloids that will foul filter and enzyme addition can help.

Enzyme Additions II Enzyme cocktails  Contain peptidase (small proteins), protease (breaks down protein), pectinase, glucosidase activity Used to help extract color and tannin from skins and will also facilitate tannin seed extraction Breakdown cell wall of skin and seed to facilitate extractions. Product does not always work Window of opportunity for enzyme addition is vague. Can make mush out of your cap

Tannin Additions Done to modify astringency and help stabilize color Many different products Mixture of tannins from different species. Different species have tannins that are different than found in grapes. Unclear whether additions are beneficial (Tannin addition products also contain volatile compounds that modify wine aroma as well) Laws allowing additions are vague and need to be updated