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
What steps are taken for whites if a wine is going to undergo MLF?
Leave a portion of lees to provide nutrients for lactic acid bacteria Keep wine warm (17-20) Top up barrels to avoid oxidation Lees usually stirred once a week Add sulfur after MLF
What do lees do to a wine?
Add texture to mid-palate
Protect from oxidation by giving off CO2
Why must wine stored on the lees be monitored?
Reduction issues (production of hydrogen sulfide which might reduce further to mercaptans (onion)) Fix: introduce oxygen using stirring
How to fix a severely reduced white wine
Pass it through a copper pipe or add copper sulfate
What aromas do hydrogen sulfide give off?
Rotten eggs!
What is a recent innovation used to stir lees?
Barrel stackers with rollers to roll the barrel - less oxygen contact
How would you stir lees in a tank?
Bubble gas through pipes attached to bottom of tank
How can rosé be made?
Drawing off method (aka saignee or bleeding)
Direct press
Blending
What is the drawing off method?
Most widely used
6-48hours on skins
All or part of juice is drawn off
Temperature affects color bc extraction happens at higher temps (cooler preferred)
What temp is rosé usually fermented at?
15-20C
What is direct pressing?
Press freshly harvested ed grapes
Cotes du Provence
What are the two types of phenolic compounds
Non-flavonoids (benzoic and cinnamic acids and resveratrol)
Flavonoids (catechins and anthocyanins)
What are tannins (specifically)?
Polymerised catechin molecules that produce astringency
Smaller tannin = more bitter
How do anthocyanins and tannins react?
They form more stable color compounds in young wines
Over time they polymerise (join together) and precipitate out, hence losing color
What does phenolic extraction depend on?
Temperature
Cap management
Duration of skin contact
ONLY HAPPENS WHEN THERE IS ALCOHOL
Is de-stemming and crushing common in red winemaking?
Hellz yeah
How much should a fermenting vessel be filled?
80% - fermenting mass will expand
What happens to red wines after they are transferred to a fermenting vessel?
Typically a small amount of SO2 is added
10-80mg/L
Controls wild yeasts, bacteria, and oxidative enzymes and aids color extraction
Then any adjustments
What is cold soaking?
De-stemmed and crushed grape must is cooled before fermentation
Below 15C for 3-7 days
80-100mg/L SO2 added (higher to prevent spontaneous fermentation)
Why are reds fermented at a higher temperature?
To extract phenolic compounds - it increases breakdown of skin cells and dissolution of phenolics
What is thermovinification?
Heat grape must to 60-80C for 20-30 minutes then cool it Max color extraction Time saver Can cause burnt flavors Not for premium wines
Where is a fermenting wine’s temperature the highest?
At the pomace cap
What is remontage? how is it done and what grapes is it used for. Benefits?
Pumping over
Drain must from the bottom and pump it over the top to break up cap.
1-3 times a day
Cab and Merlot - good for rich full bodied wines
Pros: Simple, min equipment Good extraction Disperse heat Prevents drying Oxygen Avoid bacterial spoilage on cap
What is pigeage? how is it done and what grapes is it used for. Benefits?
Punching down Gentler Pinot Noir and Syrah 1-3x over 24 hour period Merlot and Cab are more rustic this way
Pros: Gentle extraction Less likely to extract bitter or harsh compounds Good temp dispersion Avoid cap bacteria
What is delestage? how is it done and Benefits?
Rack and return
Pump the fermenting must into a separate vessel, allowing pomace to fall to the bottom
Then fermenting must is pumped back over the cap
Can be done daily but usually only twice during fermentation
Pros: Complete mixing and breaking up Aeration Extraction Seeds can be removed, reducing bitterness
Cons:
Too extractive
How does submerged cap work?
Use head boards or a perforated screen to submerge cap in the middle of the must
Pros:
No risk of drying
Cons:
Extraction difficult
What is rotovinification?
Rotofermenter is a horizontal cylindrical fermentation vessel with a motor
Mechanically mixes the fermenting must by rotating whole vessel or shaft within
Used in Aussie. Premium Nebbiolo
Pros: Fast fermentation and maceration Thorough mixing Phenolic extraction in short time Automated Eliminate need for wetting cap
Cons: Expensive Robust framework OVerextraction Reduction
What is the autovinifier called?
Algerian Ducellier system
What is autovinification?
Extended pumping over system
Stainless steel
Special vat that is sealed and as CO2 is produced it forces the fermenting must into an open reservoir and then as the level of liquid falls below gas it puts that whole reservoir back into the main chamber, mixing everything.
Pros:
No external power needed
Automated
Extraction in short time
Cons:
Extraction depends on fermnetation
Not controlled
How does desired phenolic extraction change depending on red wine style?
Poorer quality grapes = reduced extraction
Light, easy drinking reds = shorter skin contact (8days)
Full-bodied reds for aging = longer skin contact (3 weeks)
High quality vintages = extended skin contact (1month+) to soften tannins
What is often left in press wine?
Residual sugar that hasn’t fermented out
Where does MLF for reds usually take place?
In tank prior to barrel though it’s a new trend to do it in barrel for complexity
What can be released into red wines when left into contact with the lees?
Mannoproteins - thought to inhibit crystalization of potassium tartrate (more stable) and bind with tannins
How does carbonic maceration work?
Fermentation starts in the grape berry itself (intracellular fermentation)
Cover grapes with CO2
Grape respiration converts sugars to ethanol
Whole bunches
About 2% alcohol is formed, decreased malic, increase pH
1-3 weeks
Then the weight in the top berries splits lower berries to ferment normally
How does semi-carbonic maceration work?
Used in Beaujolais
DON’T cover grapes with CO2
Bunches at bottom are crushed by top and fill the vat with CO2 so that the top bunches do intracellular fermentation
What is flash expansion?
Flash detente
Place pre-heated (65-90C) grapes in a vacuum
Causes immediate cooling (30-35C) and cell destruction, release of anthocyanins and tannins
Must drained and fermented like a white
Still experimenting
What three species of bacteria carry out MLF?
Lactobacillus
Leuconostoc
Pediococcus
Malic acid>Lactic acid and CO2
What are the byproducts of MLF?
Diacetyl (buttery) - careful, can be excessive
CO2
What conditions do lactic acid bacteria like for growth and activity?
pH: 3.3-3.5
Temp: 17-20
Total SO2: Less than 50mg/L
Nutrients (dead yeast cells amino acids vitamins)
How to prevent MLF
Early clarification (reduces nutrient and bacteria levels) SO2 addition (free levels>25mg/L) Low storage temps (<12C) Low pH (<3.1) Cleaning and maintenance of containers Sterile filtration at bottling
How to encourage MLF
Lees aging Low levels of SO2 before fermentation Warm temp (18-22C) Add freeze dried lactic bacteria Increase pH (>3.3)
How to test for malic acid presence
Chromatographic test Enzymatic analysis (expensive)
What does MLF do?
Deacidification
Stability (as long as pH remains low)
Loss of primary fruit aromas
Add aromatic compounds
Increased levels of VA (citric acid broken down by bacteria)
Spoilage potential (if bacteria activity is not controlled)
What is one way to create volatile acidity?
Citric acid broken down by yeast or bacteria
Should sparkling wines undergo MLF?
Base wines should before secondary fermentation. If the pH is low enough it may not be necessary.
What is liqueur de tirage and what is it made of?
Added to base wine to induce secondary fermentation
Sucrose (beer or cane sugar) + yeast
How much does ABV increase during traditional method secondary fermentation?
1.2-1.3%
What is remuage?
Riddling
What is liqueur d’expedition?
Dosage made of sugar and wine
To what temp is the wine cooled during the tank method, before dosage is added?
-5C
At what point are VDN wines fortified?
5%ABV
95% grape spirit
How much is Port must sulphited?
90-100 mg/L SO2
At what temp is Port fermented?
30C
At what point are Port wines fortified?
6-9%ABV
77-79% grape spirit
1 part spirit to 4 parts wine
What is Port traditionally matured in?
“pipe” 550L
What parts of Palomino juice is used for what sherry?
First 70%: Fino/Manza
next 20%: Oloroso
How is Sherry pressed?
Horizontal press in the vineyard
What vessel is Sherry fermented in? What temp?
Steel or 600L oak butts
25-30C
11-11.5%
What ABV are Finos foritifed to? Oloroso?
14.5-15.5
18
What kind of barrels are used in the solera system?
600 or 650L butts
What does flor need to survive?
Alcohol, glycerine, and oxygen
Temp 15-20C
What is acetaldehyde?
Sherry-like aromas
