Harvesting and processing Flashcards
Regarding agrochemicals, what must you do in the vineyard before harvest?
There is a minimum number of days for last application before harvest. Causes fermentation and health problems. Late sulfur can cause problems with hydrogen sulfide
What late applications cause problems with fermentation?
Copper-based sprays (brown haze)
What pre-vintage plans must be taken into consideration?
Estimate crop levels for tank space
Check and clean harvesting and processing equipment
Clean tanks
Purchase necessary products
Advantages/disadvantages of manual harvesting?
Good: No damage Select individual bunches for ripeness No terrain, spacing, training limits Little equipment needed
Bad:
high labor needed
Slower
When was machine harvesting first introduced and what were machines like? Now?
1960s - vertical metal fingers that beat the vine
Now - fiberglass rods strike foliage horizontally, then horizontal conveyor belts
Pros/cons for machine harvesting?
Good:
Speed
Night harvest
Lower costs
Bad: Berry damage Imprecise selection unless new machine Expensive machine purchase Terrain issues Must have specific trellising systems Rows must be ride enough
Techniques for limiting berry damage during picking and transport
Shallow picking containers Limit moving grapes Reduce load level and dumping heights Refrigerated truck Minimize delay between picking and processing
What are the main concerns between picking and processing?
Oxidation (causes brown juice and loss of aroma)
Microbial growth
Contamination
How to limit oxidation before processing
Limit air contact (blanket with CO2 or N)
Add sulfur dioxide to freshly harvested grapes
Harvest when cool (rate of oxidation increases as temp increases)
Process quickly
What is microbial growth affected by?
Health of grapes
Hygiene
Temperature and time
Berry integrity
How can contamination occur before processing?
Rainfall (dilutes sugar) Leaves and stalks in bins Picking shears in picking bins MOG harvested by machines Soil, oil, metal or plastic tains
What is MOG?
Material other than grapes
De-stemming advantages and disadvantages (for whites and reds)
Good:
- Removal of stems which can be herbaceous and bitter when unripe
- Removal of MOG
- More fruit can fit in press (whites)
- Stems can absorb color and alcohol (reds) and release more water and K
Bad (whites):
- Cheap destemming machine can damage stems and release bitter flavors
- Pressing without stems is slower
- Pressing whole bunches releases fine juice with low phenolics and solids (bc fast drainage)
Bad (reds):
- Increased compaction in the cap = more difficult temperature control and phenolic extraction
- Tannins in stems can be good to fix oxidation and color
- Slower pressing
When is de-stemming definitely NOT done?
Sparkling wines
Carbonic maceration
When can sorting be done?
Before destemming, after, or both
How does destemming work?
Spinning perforated drum allows berries only to pass through perforations and stems are pulled away by contra rotating blades
Why are grapes crushed?
Release juice so it is immediately available to yeast
Faster pressing in white winemaking (free run juice is liberated first)
Increase in tannin and color in reds (more contact)
Why not crush? Where?
semi-carbonic maceration keeps some whole berries intact
Spain, Beaujolais, Languedoc-Roussillon (Carignon)
How does crushing work?
Grapes passed between two rollers that break open berry skins
White: can be chilled prior to pressing
SO2 often added
What is pressing and when does it occur?
Using pressure to grapes to squeeze the liquids from the solids - gentle but increasing pressure
Whites: usually ASAP after reception (whole bunches or destemmed and crushed grapes). Free run juice drained first
What percentage of the total weight should pressing extract?
About 70%
Which white grapes might benefit from skin contact? Why?
Sauvignon Blanc Semillon Muscat Gewurztraminer Riesling Extract aromatic compounds but a richer style of wine also results
What aids extraction when doing white wine skin contract?
A pectolytic enzyme
What temperature is generally used when doing white wine skin contact? How long?
5-10C
3-24 hours
What is the concern of using skin contact for whites?
Releasing bitter phenolic compounds
What is press wine?
The wine released by pressing grape pomace at the end of fermentation and post-fermentation maceration
Reds
Is usually tannic and dark in color - can be astringent and bitter
Types of presses?
Vertical screw press/basket press Horizontal screw press (Vaslin) Pneumatic press (Willmes) Tank press Continuous screw press
How does a basket press work? Pros/cons?
Grapes are placed in a cylindrical basket and a removable lid is placed on top. Pressure is applied to top against a stationary plate at bottom. Liquid seeps out between slats and is collected.
Good:
Simple and easy
Filtered through stalks/pomace as extracted, giving clear must
Bad:
Slow and labor intensive
Long time
Exposed to oxygen
How does a horizontal screw press work? Pros/Cons?
Basket press on its side with pistons at either end
Stainless steel screw running through center
Pistons move together
Pros:
Simple to fill and empty
Operation can be automated
Partially protected from oxidation by blanketing receiving tray with gas
Cons:
Breaking up the pomace between cycles is violent (extracts phenolics)
High pressures = reduced quality
How does a pneumatic press work? Pros/Cons?
Horizontal but with a pneumatic bag/membrane that can be inflated by air or water
Grapes are place in between bag and drum which presses against the holes and liquid passes through
Pros:
Good liquid extraction at low pressure
Gentle breaking of pomace
Cons:
Longer press cycle
What is the tank press? Pros/cons?
Variant of pneumatic
Pressing occurs in a closed tank that can be pre-flushed with inert gas
Grapes put in a non-perforated tank and pressed against internal drains by bag
Pros:
No oxidation
Low pressures high extraction
Cons:
Longer press cucles
Expensive
What is the continuous screw press? Pros/cons?
Used for large quantities as it isn’t a batch press
Perforated drum with screw inside
Grapes loaded into one end and then screw pushes the grapes towards resistance at far end to expell liquid from perforations
Pros:
Continually loaded, high output
Cons:
Higher pressures and rough screw=lower quality uice
What is SO2?
A colorless but toxic gas used since 17th century in winemaking
How much SO2 is produced by yeast in fermentation?
10mg/L
Why is SO2 used in winemaking?
Antiseptic (inhibits development of microorganisms)
Antioxidant (combines with oxygen so doesn’t oxidize)
Antioxidasic (Denatures enzymes that propel oxidation)
Combines with Acetaldehyde (byproduct oxidation)
How is sulfur added in wineries (what forms)?
Potassium metabisulfite powder (can be dissolved in an acid solution) - harvested grapes directly
Pure SO2 gas in liquid form
Dissolved in solution (5%)
Burning sulfur tablets or candles (in barrels)
What are the general recommendations for sulfur additions in grape must?
White: 60-100 mg/L
Red: 10-60 mg/L
Why would sulfur additions be increased?
Style of wine (more aroma preservation = more sulfur)
Grape health
pH (more pH = higher SO2)
What is the total sulfur dioxide?
The sum of free SO2 and bound SO2 present in juice or wine
What is free SO2? How does it exist in wine?
Portion that is active and has protective properties - only molecular SO2
Two parts:
Active molecular SO2
Dissolved in present water to form sulfurous acid
How does pH relate to active SO2?
In free SO2, only the molecular SO2 has any protective properties, although all free SO2 is active. The amount of molecular SO2 that is dissolved into sulfurous acid is dependent o pH.
Lower pH = higher molecular SO2 remaining
What is bound SO2?
The portion of sulfur dioxide that has combined with various components in grape must. (sugars, aldehydes, ketones)
It is inactive at this point
What are the maximum limits for total SO2 in dry and sweet wines?
Dry red: 150 mg/L
Dry white: 200 mg/L
Off-dry (5g/L sugar): 250 mg/L
Lusciously sweet BA/TBA, Sauternes: 390 mg/L
Organic wines lower
Sweet is higher bc sugars bind with SO2 readily
Why clarify a grape must? How?
Whites and rosés
Remove solid particles suspended in must = cleaner flavors and less bitterness
Ways: Cold settling Centrifugation Diatomaceous earth filtering Flotation
NOTE: Fermentation necessitates clarification again
How does cold settling work?
Simple and effective - uses gravity - HIGHEST QUALITY
Settle pressed must overnight between 5-10C
suspended solids sink to the bottom and clear must is racked off
Pectolytic enzymes can be used
How does centrifugation work?
Separate solids at high speed by centrifugal force
Harsh and oxidation risk BUT very clean
Expensive
Large wineries
How does diatomaceous earth filtration work?
Filter with a diatomaceous earth filter
Used for aromatic varieties
Can reduce nutritional content too much = yeasts struggle to ferment
How does flotation work?
Bubble small amounts of air (N, CO2) through cloudy must from bottom
Bubbles catch solid particles and float to surface
Rarely used
Large wineries
How is enrichment done?
Add either sucrose (beer sugar or cane sugar) = chapitalization
^^^ cheaper and more netural
Add concentrated unfermented grape juice aka rectified concentrated grape must (RCGM)
What is RCGM?
Rectified concentrated grape must used for enrichment
How much does each kilogram of sugar increase a wine’s volume by?
1kg=.63L increase
Generally, how much sugar does it require to raise ABV by 1% (white and red)?
White: 17g/L
Red: 19g/L (higher fermentation temp and pumping over = evaporation)
Techniques for concentrating must
Concentrates grape juice by removing water - a form of enrichment
- Cryoextraction
- Reverse osmosis
- Vacuum evaporation
How does vacuum evaporation work?
Used since 1989 in France
Evaporate must in a vacuum
Evaporates at 20C to minimize loss of aromatic and flavor potential
What is reverse osmosis and how does it work?
Filtration technique that is superceding vacuum evaporation
Uses differences in molecular weight
High pressure applied to must along a membrane filter - water passes through membrane
Concentrates EVERYTHING even off flavors and unripe tannins
ALSO USED FOR removing alcohol and volatile acidity
What is cryoextraction?
Freeze fresh grapes until water freezes, press solids and frozen water off
OR freeze grape must (controversial)
What are the level rules for concentrating musts?
Musts may not be enriched by concentrated by more then 2% potential alcohol
OR by a maximum reduction in volume of 20%
Whichever is lower
What is potential alcohol?
Concentration of alcohol that would result from the fermentation to dryness of all the sugar dissolved in a must
What is actual alcohol
Actual level of alcohol in a wine after fermentation
What is total alcohol?
The actual alcohol plus potential alcohol from residual sugar
What is natural alcohol?
The total alcohol in an unenriched must or wine
How much can total acidity be reduced by?
no more than 1 g/L (expressed by tartaric acid)
Forbidden in warmest regions
How to de-acidify?
- Add potassium bicarbonate post-clarification, pre-fermentation (preferred) - only tartaric
- Add calcium carbonate (high levels of calcium tartrate form which are harder to remove and tartrate-unstable) - only tartaric
- Double-salt deacidification (add special calcium carbonate which has calcium tartrate-malate added) Removes both tartaric and malic acids
- Malolactic fermentation - only malic
When might the expense of a double salt deacidification be justified?
In very cool regions when malic acid levels don’t have a chance to fall with ripening
Typically tartaric is the main acid so it isn’t necessary
What is a risk of de-acidification?
pH raises which increases the risk of microbial infection and decreases SO2 effectiveness.
Why don’t titratable acidity and pH correspond directly?
1) Buffering effect of dissolved salts
2) pH is a logarithmic scale while TA is a linear scale
How does pH affect color in red wines?
Low pH = brighter and more blue/purple
High pH = duller and more garnet/brown
What type of acid is used for acidification? When? What are the legal EU limits and where?
Tartaric acid Before fermentation (better integration) Must: 1.5 g/L Wine: 2.5 g/L Only in CII and CIII zones Some exceptions in very warm years
What is the limit for citric acid? When should it be added?
Not as desirable as tartaric acid but increases stability
Total citric acid concentration: 1g/L
Add AFTER fermentation because it can be metabolised into acetic acid aka volatile acidity during fermentation
What are other additives to must?
- Tannins
- Bentonite: form of clay used as a fining agent in white wines to remove dissolved proteins (usually after fermentation but sometimes before depending on winemaker preference)
- -Also removes flavor compounds so use sparingly
Why might a winemaker choose to handle a must oxidatively?
Some varieties show that this leads to more complex aroma and flavor development
ie: Chardonnay
What is hyperoxidation?
The enzymatic oxidation of phenolics which converts them to insoluble polymers that can be removed by clarification
Result: more stable wine
Bubble oxygen through a wine for a length of time
For which varieties is hyperoxidation most effective when it comes to color stabilisation?
Alsatian German Chardonnay Chasselas Garganega Trebbiano
NOT SAUV B
What does excessive oxygen exposure do for must?
Produces acetaldehyde (sherry like flavor)
Creates bitter components from phenolic oxidation
Develops spoilage bacteria
What is ascorbic acid and why is it used?
Vitamin C
Supplements SO2
Can’t replace it bc no antiseptic effect
Forms Hydrogen peroxide without the presence of SO2
