REDUCTION, SULFATES & LIGHTSTRIKE By Tiffaney and Mackenzie GWS 410 ~ Fall
REDUCTION An oxidized compound that gains an oxygen atom and loses an electron because it to becomes reduced when it gains another electron.
REDUCTION Oxidation-Reduction (Redox Potential) • The potential of the wine to hold its oxygen atoms • Is an exchange of electrons and oxygen between the atoms • Process happens in stages • How smelly sulfur compounds get in the wine
Reductive Environment Low Redox Potential Allows reduced sulfur compounds to develop Is effected by (HIGH) pH levels Leads to stinky wines High Redox Potential Will precipitate out and has a better hold on oxygen pH levels are low
Sulfur Important for the fermentation process while also being byproduct Non-mental Element in 2 amino acids created when yeast cells absorb sulfur: Cysteine and Methionine Yeast utilize it in the juice (and fermentation) to produce Hydrogen Sulfide (H2S)
Sulfur HEAVY High perception threshold Happens during yeast metabolism during fermentation not after Big problem: cant use aeration or copper 50-1200ppm • LIGHT • Low perception threshold • Happens during fermentation and/or aging • Use of aeration, sparging, and copper can be used • Usually >1ppm
so2 • Sulfur Dioxide (Sulfites) • Used by winemakers • Binds with aldehydes to “stable” and preserve the wine • Smells: Matchstick • Sensory: 66ppm in white wine • 100ppm burns the nose • 150ppm is undrinkable
so2 • 2 Primary actions: • anti microbial agent • anti oxidant • -For white wines added before fermentation and added after to stop malolacticfermentation • -For reds to stabilize color before fermentation • Also capable of taking on another oxygen atom to become S03 • S02 has the capability when combined with H20 to become • Sulfuric Acid • S02 + H20 = H2S04
S04 • Byproduct of plant and animal decay
H2S • Hydrogen Sulfide • Needs yeast cells that are nitrogen starved to increase • Light sulfur compound • If in the wine it is not noticeable early on, but can be fixed with SO2 or splash racking if caught early on. • Smells: Rotten Egg • Sensory: 1ppb
Mercaptans • Also known as: Thiols • Result from the reaction of H2S with alcohol or amino acid sulfurs • Do not aerate • Cure with copper sulfate • Smell: Cabbage, Rubber, Garlic, (at worst) sewer gas.
LiGHTSTRIKE • Wines that have had excessive exposure to ultraviolet light. • Delicate varietal wines like Champagne are especially perceptive to lightstrike. • Red wines are rarely affected due to the phenolic compounds present within wine that protect it. • Caused by sulfur containing amino acids that react with naturally occurring vitamins that are destroyed by UV light. This reaction creates smells and tastes.
LiGHTSTRIKE • Fault causes: aromas and tastes of wet cardboard, wet wool, rotten egg and vegetal smells. • Prevented by: • -Bottling in dark bottles • -Storing wine in dark places • In France lightstrike is known as "goût de lumière", which translates to a taste of light.
LiGHTSTRIKE • Blocks 90% of UV Rays Blocks 10% of UV Rays Blocks 50% of UV Rays * Can differ depending on thickness of glass, label placement and intensity and angle of light source.
LiGHTSTRIKE • Where does lightstrike happen most? • Stores that use florescent lighting • Display Cases • Refrigerators • How to avoid it: • Look for dark glass bottles • Don’t pick bottles from top shelves • Avoid window and refrigerator displays.
3 things to Remember • What wines does Lightstrike affect and how can you prevent it? Lightstrike affects white wines and rarely red wines. It is prevented by using dark glass for wine bottles and storing bottles in dark places. • 2. What are the two amino acids produced when yeast cells absorb sulfates? cysteine and methionine • 3. What are three identifying smells for reduction? ie: rotten eggs, rubber, burnt matchstick