Fermentation Flashcards
What is the fermentation formula?
C6H12O6 > 2C2H5OH + 2CO2 + energy
glucose/fructose > ethanol + carbon dioxide + energy
Broken down anaerobically by YEASTS
Generates heat
What yeast genus is primarily responsible for fermentation? Species?
Saccharomyces
Saccharomyces cerevisiae
How much sugar is needed to create each 1% ABV?
16-18g/L
How many g/L of alcohol is each 1%?
8g/L
The rest becomes CO2 gas
When sucrose is added for enrichment what does it become?
Broken down into glucose and fructose
How do glucose and fructose differ?
MOLECULES ARE IDENTICAL
Glucose = easier to digest by yeast
Fructose = harder to digest and sweeter to humans
What does the rate of fermentation depend on?
Concentration of sugars originally present Availability of oxygen Temperature, Type and quantity of yeasts Nutrient content of grape must absence or presence of SO2
What stops fermentation?
When all sugar is gone When alcohol is too high for yeasts and they die Adding alcohol Adding SO2 Chilling must
What are byproducts of fermentation?
Glycerol (colorless, viscous, with slightly sweet taste) Acetaldehyde Ethyl acetate Aroma esters Fusel oils
What fermentation vessels are common and why?
Stainless steel tanks: temperature control easy, can be automated
Wooden: retains heat more (bad). Bacteria and yeast can develop if not cared for properly. Popular for reds because the heat aids extraction and solid to liquid content is high
Cement: lined with epoxy resin, tiles, wax, or glass. Cheap to install, easy maintenance. Large resistant to changes in temp
What types of wooden vessels are used around the world?
piece (228L) in Burgundy barrique (225L) in Bordeaux. Large in Germany, Alsace, Loire and Italy. Barrique in New World. Open topped wooden vats across Europe
Oak, chestnut, acacia, cherry, walnut
Name some species of wild yeasts on grapes. Which one carries out full fermentation and at which point?
Kloeckera (CAN START FERMENT)
Hanseniaspora (CAN START FERMENT)
Candida
Metchnikowia
QUICKLY DOMINATED by Saccharomyces species, present in many wineries. By the time the wine reaches 4%
Why choose not to inoculate?
Said to produce more complex wine (more yeast species are involved = more chemical reactions and products)
Risk: some produce undesirable flavors
What is a pied de cuve?
A starter culture of indigenous yeasts that will be allowed to ferment until Saccharomyces cerevisiae is present (then that culture is used for next ferments)
Why choose to inoculate with active dry yeast?
Rapid fermentation onset (impt because off flavors and spoilage) Ability to ferment highly clarified juice Rates more even, controlled No funk Efficiency No stuck fermentations usually Low volatile acidity Some help deacidify
What is Lalvin Rhone 2226 used for?
tolerance to high sugar levels
What is Lalvin Rhone 2323 used for?
Extraction of phenolics and tannin structure
What is Maurivin Cru-Blanc used for?
high glycerol production
What is Lalvin R2 used for?
Low temp tolerant yeasts = fruity whites
What is Lalvin EC-1118 used for?
Low foaming for secondary fermentation
What is Lalvin K1V-1116 used for?
SAuvignon Blanc
Should cultured yeast batches have lower or higher amounts of SO2?
Higher - stops wild yeasts from spontaneously fermenting. Cultured yeasts have higher tolerance to SO2.
What scales are used to monitor fermentation and how do they work?
DENSITY measuring
Before fermentation they measure the amount of sugar in must
After, they measure decrease of density which corresponds to rate of fermentation
-Baumé: relative density, used in France
-Brix: hydrometer measurement, used in Aussie, NZ, US
-Oechsle: hydrometer scale: Germany and Switzerland
Babo: Italy
KMW: Austria
Why is temperature control important during fermentation?
Controls rate of fermentation
What is the ideal fermentation temperature for whites and reds?
Whites: 10-18 (most commonly between 14-20)
Reds: 20-32 (ideal: 25)
Grape must can be chilled prior to ferment to help
What do excessively high or low temperatures during fermentation do?
High:
Encourage oxidation, spoilage, instability
Loss of aroma and flavor or alcohol
Yeast becomes sluggish (shuts down by 35-38C)
Low: Whites: retention of isoamyl acetate (banana) Red: Poor extraction Sluggish fermentations high levels of ethyl acetate (volatile)
What is ethyl acetate?
Volatile acidity
When does a winemaker begin to suspect that fermentation is complete?
When the relative density of the wine drops below 1. Check sugar levels after this.
How much unfermentable sugar can be found even in dry wines?
Up to 2 g/L
What might a winemaker do immediately post-fermentation for an aromatic dry white?
Chill wine
Add sulfur (40-100mg/L) to block malo
Lees settle and rack, bottle
What might a winemaker do immediately post-fermentation for a full bodied Chardonnay fermented in oak?
Extended lees contact and stirring
MLF
Sulphited
Mature in oak
Why do stuck fermentations happen?
Fermentation is too hot (above 35) or too cold (depends)
Nutrient levels depleted
Indigenous yeasts might die off from alcohol
How to fix a stuck fermentation?
Adjust temperature
Add nitrogen-rich products (DAP or vitamin B)
Re-inoculate
Usually a combo
How to prevent stuck fermentations?
Aeration at beginning of fermentation
Add 100-150mg/L DAP or .5mg/L thiamine
Temp control
What kinds of musts might have nutrient issues? How to fix?
highly clarified musts or made from rotten fruit
Add DAP or thiamine
Why does hydrogen sulfide form?
Yeasts that are deprived of nitrogen break down amino acids instead, creating H2S
What is key to making a good white wine
Harvest healthy ripe grapes and process them quickly, fermenting at cool temps and protecting the must and new wine from oxidation
What temp may white wines fermented in small barrels reach?
25C
What temp might an aromatic white wine be fermented at
11-15
ISOAMYL ACETATE
What temperature is normal for whites for yeast settling post-ferment?
12C
How much sulfur is usually added to block MLF in whites?
40-50mg/L