Flashcards in Vini 1: Harvesting and Processing Deck (54)
ECP - Estimation (of crop levels), cleaning (of necessary equipment) and purchasing (of oenological products).
Pros and cons of hand harvesting:
Minimal damage to bunches, selection of best grapes (whole bunch, carbonic), any terrain style and little equipment needed. BUT, slower and higher labour input. Can be obligatory by law.
Pros and cons of machine harvesting:
Speed/intervention (use of fibreglass rods), night harvesting and labour costs reduced. BUT, grapes damaged (oxidation risk), less selection, machines pricey/in high demand, needs suitable trellis, wide rows and not suitable for some terrain.
Limiting fruit damage in transit:
Shallow picking containers, limiting container transfers, reducing load levels, refrigerating trucks and minimising delay before processing.
Minimising oxidation risk:
Blanket grapes (CO2, N), add SO2, harvest at cool time (morning or night) and minimise delays.
Dilution (rainfall), leaves/stalks in bins, picking shears left behind, MOG and soil/oil/taints in bins.
Why is grape processing more efficient in white winemaking?
Because the fruit is de-stemmed.
Why are stems sometimes undesirable in red winemaking?
Because they release water and potassium and they absorb colour and alcohol.
Downsides of de-stemming (whites):
Machine damage, slower pressing (no natural drainage channels) and juice not as fine (for same reason).
Downsides of de-stemming (reds):
Harder to control temp./phenolic extraction, don't get the good tannins found in some stems and slower pressing.
Objective of crushing:
To release juice that is immediately available to yeast for fermentation.
Crushing (reds and whites):
Faster for whites (free-run juice available immediately). Increased colour and tannin extraction for reds.
Grape which sometimes has to have semi-carbonic maceration by AC law?
Chills white grapes before pressing.
Good extraction level at pressing:
ca. 70% of total weight.
Skin contact in whites:
Pectolytic enzyme often added to help extraction. 5-10 degrees for up to 24 hours.
Pros and cons of basket press:
Simple, produces clear must/wine. BUT, slow, labour-intensive, can release bitter phenols and oxygen exposure.
Pros and cons of horizontal screw press (e.g. Vaslin):
Easy to fill and empty, automated and blanketing possible. BUT, can be violent (over-extraction) and high pressures can reduce quality.
Pros and cons of pneumatic press (e.g. Willmes):
Good extraction and more gentle. BUT, slower.
Pros and cons of tank press:
Can be flushed with inert gas, good extraction. BUT, slower and most expensive of all.
Pros and cons of continuous screw press:
Very high, uninterrupted throughput and modifications can be made in output tray. BUT, produces lower quality juice/wine through rough action.
Purposes of sulfur dioxide (SO2):
Antiseptic, antioxidant, antioxidasic (denatures oxidising enzymes) and combines with acetaldehyde.
Recommended SO2 amounts:
White musts: 60-100mg/L. Red musts: 10-60mg/L.
SO2 for higher pH wines:
Need more because less is in the active form.
Maximum SO2 from 2009 vintage:
Dry reds: 150mg/L (contain natural antioxidants). Dry whites: 200mg/L. Sweets can have higher levels, due to binding powers of sugars.
Pre-fermentation clarification (white and rosé):
Cold settling, centrifugation, diatomaceous earth filtering or flotation.
Very common. Must left to settle (often overnight) at cool temp. (5-10 degrees). Gravity sends suspended solids to bottom and can then be racked off. Possible addition of pectolytic enzymes - destroy pectins that suspend the grape flesh in the must.
Use of centrifugal force. Considered harsh by many. Expensive and oxidation risk also high. Used in big wineries where efficiency is key.
Diatomaceous earth filtration:
Good for aromatic varieties. BUT, complete solid removal can reduce must's nutritional content, meaning yeasts struggle to start fermentation.