Ch. 13 General Winemaking Options Flashcards
Why is oxygen generally threatening for the production of fresh, fruity wines?
- loss of fruitiness - aroma compounds that give wines fruity style (thiols in SB for ex) break down w oxygen
- oxidation reactions can contribute unwanted aromas to wine - ex acetaldehyde and its nutty, apple aromas
- color becomes darker - gold then brown
- threat of bacterial spoilage is greater
** phenolics in red wine protect more against oxidation
What does reductive or protective winemaking refer to? What techniques are involved?
The practice of minimizing oxygen exposure during winemaking process.
- avoiding ullage
- ullage is headspace of air between wine and top of container –> fill to top, or “top up” w more wine, especially in wooden vessels where evaporation happens - use of inert gases - nitrogen, carbon dioxide, argon flush out O2 –> add to presses, pipes, vessels or to fill ullage
- addition of sulfur dioxide
- use of impermeable containers - stainless steel, concrete vs wood
- cool, constant temperatures - slow rate of oxidation - so storage in fridges after picking, picking at morning, maturing wine in cool cellars
What are benefits of controlled oxidation?
- Oxygen is required at the start of fermentation of all wines to promote healthy yeast population
- lack of enough O2 in winemaking or storage can lead to reductive off flavors
- white wine - exposing must to oxygen before fermentation helps w oxidation stability and aging potential
- red wine - O2 essential for color stability (bc of reaction between anthocyanins and tannins)
- lack of complexity - some wines need exposure to oxygen to develop a range/diversity of flavors from oxidation, essential to wines like Oloroso Sherry, Madeira, Tawny Port (dried fruits, honey, caramel, coffee, leather, mushroom
What are some techniques to increase oxygen exposure? Considerations?
- cap management techniques - spray/splash must
- small wooden barrels - O2 permeates, small volume of wine so effect is greater
- increasing interventions - rackings, lees stirring
- allowing ullage
- techniques that pump oxygen through must or wine
- Wines exposed to oxygen must be carefully monitored for spoilage organisms encouraged by oxygen, like Brettanomyces and acetic acid bacteria
What are the effects of sulfur dioxide in winemaking?
- anti-oxidant - reduces the effects of oxidation by reacting with the product of oxidation reactions
- anti-microbial - reduces risk of bacterial spoilage by inhibits development of microbes such as yeast and bacteria
What determines how much SO2 is found/needed in a wine?
- Naturally ocurring during fermentation (10 mg/L or less)
- Local laws (diff areas regulate depending on style of wine eg 150 mg/L max for red in EU)
- Winemaking practices - organic, natural
- winemaker preferences - high levels of SO2 can dull wine aromas/flavors and can sometimes cause wine to taste harsh
- good practice - hygiene and keeping grapes/must/wine at cool temps reduce amount of SO2 needed
What is the difference between bound SO2 and free SO2?
Bound So2 –> dissolved, reacts with compounds in must or wine, ineffective against oxidation and microbes
Free SO2 –> not bound, relatively inactive, small proportion exists as molecular SO2 which is effective against oxidation and microbes
What influences the efficacy of SO2?
- pH level of must or wine –> more SO2 needed at higher pH levels (lower acidity) to protect against oxidation, spoilage
- timing and size of SO2 additions - more effective to add larger amounts fewer times (at crushing, end of malo and bottling)
What are the threats posed to grapes during transportation to the winery?
- oxidation- loss of fruitiness, unwanted aromas, spoilage risk
- ambient yeasts- start fermentation early if grapes have split
- acetic acid bacteria (turn alcohol to acetic acid, vinegar-y smell)
- high temps during harvest increase risks
- black grapes less vulnerable to oxidation bc phenolics have anti-oxidative properties
What measures can be taken to minimize threats of oxidation and microbial infection?
- harvesting, transporting grapes at night when temps are cooler; harvesting at sunrise if by hand
- addition of SO2 at time of harvesting
- cold storage once received at winery (Albariño, Lagar da Condesa, fridges)
- Sanitizing harvesting equipment/bins
- Collecting/transporting grapes in small crates to minimize crushing
What are the options for physical transport to the winery?
Hand harvesting:
- grapes put in small crates, transported to winery like this –> minimize crushing, prevent oxidation and spoilage
EX - Champagne - where PN or PM are destined for white wine - need to prevent extraction of phenolics or colors; small-scale one hectare harvest and can use own tractor
- small crates tipped into large bins - involves some crushing, threat from spoilage, some growers add SO2
Machine harvesting
- fruit already de-stemmed, transported in large containers, some release of juice, add SO2
What processes take place at grape reception?
Depending on hand or machine harvested, health and quality of grapes:
- Chilling
- Sorting phase
- Destemmer/crusher
What are the advantages and disadvantages of chilling grapes at winery?
- chill to lower temps before crushing and pressing begins
ADV
- help preserve fruity aromas
- help reduce spoilage threat
- fridges can serve as storage if other equipment in use
DIS
- chilling takes time from processing of grapes (heat exchangers work more quickly than fridges)
- cost of equipment and energy
What determines the level of sorting required?
- ripeness and health of fruit arriving at the winery - poor years/cool climates may require sorting to remove mouldy/under ripe grapes
- intended final wine quality and price –> more sorting=more cost (labor, time, lower yields/less wine) ** key to determine quality of wine made in relation to price gained for wine
- whether sorting has been carried out in vineyard
- physical state of grapes (bottom grapes in large containers already crushed partially)
What are the sorting options for quality wines?
- remove unwanted grapes/bunches before picking/hand harvesting
- sorting by hand on table or moving belt (which removes MOG, can be done before or after destemming or both)
- Optical sorting - using digital imaging and software to scan - costly, usually for premium or super premium wines
What considerations need to be made in relation to de-stemming?
In which situations are stems not removed?
- Stems might add unwanted greenness to tannins
- Fermentation with stems absorbs some alcohol
- Red wine fermentation that use some whole bunches (PN in Burgundy)
- carbonic maceration (Gamay in Beaujo)
- whole bunch pressing for some white wines (high quality sparkling wine)
What happens during crushing?
At beginning of winemaking process, application of enough pressure to grapes to break skin and release juice, making it available for fermentation
Needs to be gentle enough to not crush seeds, which add phenolic bitterness
Can be combined w destemmer-crusher machine - so sorting can be done at level of whole bunches
Define must
Mix of grape juice, pulp, skins and seeds that comes from crusher
For white wines, must may also refer to grape juice that is fermented
Typically refers to substance that is being fermented
What are differences and similarities in pressing for white vs red wines
WHITE: grapes pressed to extract juice, separate skins before fermentation
RED: grapes crushed before ferment, pressed after desired number of days (when ferment starts w/skins and continues off, some lighter reds) on skins or after fermentation
SIMILAR: soft pressing is important, don’t want to extract any (in white) or excessive tannin and bitterness from skins and seeds
Describe mechanism of pneumatic press. What are advantages and disadvantages of a pneumatic press?
- Bladder inflates with gas inside a cylindrical cage, grapes pushed against grates separating juice or wine from skins
Also called air bag presses
ADV
- can be programmed to exert diff amounts of pressure - can create diff blending components for added complexity
- can be flushed w inert gas to protect from oxidation
DIS
- need to afford initial investment
better suited to medium to large scale wineries
Describe mechanism of basket press. What are advantages and disadvantages of a pneumatic press?
Also called vertical press, champagne press
Basket is filled with grapes and pressure is applied from above. Juice runs though holes on the side, collects in a tray at bottom, pipe transfers juice to another vessel
ADV:
- gentler than pneumatic
DIS
- aren’t sealed, can’t be flushed with inert gases
- hold smaller press load
- more labor intensive
- better suited to small wineries making premium wines
What are other types of presses?
- Horizontal screw press - similar to basket press, mounted horizontally above draining tray - less gentle, less popular
- continuous press - only one of discussed presses that doesn’t require batch processing - grapes can be loaded onto press continually - allows for quicker pressing of large volumes, less gentle–> better for inexpensive, high-volume wines - cheap, bulk wine
