Unit 2 - Week 5 Flashcards
Creation of hydrogen sulfide and other stinky reductive compounds during fermentation is caused by
late sulfur application on black grapes
Adversly effect on yeast growth and activity is caused by
residual fungicides
Brown haze, potentially toxic levels of copper salts in the wine are caused by
copper-based sprays
What leads to browning of grape juice, potential loss of aroma compounds
oxidation
As temperature increase the rate of oxidation will
increase
What need to be done to reduce the treat of oxidation
limit contact with air (some harvest trailers will immediately blanket grapes with carbon dioxide or nitrogen) add small amount of sulfur dioxide to fresh harvested grapes to deactivate oxidising enzymes
Microbial growth is affected by
health of grapes hygiene temperature and time berry integrity
Contamination by occur by
rainfall (dilute sugar) leaves and stalks picking shears material other than grapes soil, hydraulic oil, metal or plastic taints.
What is material other than grapes
mechanical harvesting (leaves, stalks, canes, insects, lizards, etc
In red winemaking stems release what
water and potassium which is undesirable, also absorb color and alcohol
Why is grape processing more efficient when de-stemming occurs in white wine making
allows more fruit to fit into press
For production of white wines what are de-stemming disadvantages
pressing without stems is slower as stems provide drainage channels if its done wrong more bitter and herbaceous flavors are released pressing whole bunches release fine juice with low phenolics and low solid due to rapid drainage
For production of red wines what are de-stemming disadvantages
stems will reduce compaction of the pomace cap in fermentation tank, make temperature control and phenolic extraction easier in some varieties stems release good quality tannins which reduce damage done by oxidation, can help to fix color in wine stems increase speed and efficiency of pressing by providing drainage channels
What is added during crushing process
sulfur dioxide
In production of white wines pressing temperature, duration
between 5-10 C, few to 24 hous
In production of white wines why is pectolytic enzyme added
to aid extraction. aim is to extract aromatic compounds but a richer, fuller styl also results. danger is that bitter phenolic compounds may be extracted.
What white varieties may benefit from shor skin contact prior to pressing
Sauvignon blanc, muscat, riesling, gewurztraminer, viognier.
In production of red wines, pressing of the pomace at the end of fermentation release
more wine which is high in tannin and color. sometimes a portion is add back to wine but sometimes is too astringent and bitter.
This type of press is traditional, cylindrical basket, pressure from the top
Vertical screw press (basket press)
Vertical screw press (basket press) advantages
simple, easy to use, gives clear must or wine
Vertical screw press (basket press) disadvantages
filling and reloading is slow, labour intensive, requires time, risk of extracting bitter phenols, risk of oxidation
What is the name of the press that is basically basket press turned on its side
Horizontal screw press (Vaslin)
Horizontal screw press (Vaslin) advantages
filling and emptying is simple, automated, liquid can be protected from oxidation by blanketing with inert gas
Horizontal screw press (Vaslin) disadvantages
high pressure, reducing potential quality, violent breaking up marc results in extraction of phenolic and astringent matter from skins, seeds, stems
What is the difference between Horizontal screw press (Vaslin) and Pneumatic press (Willmes)
Pneumatic press (Willmes) is also basket press turned on its side but inside is cylindrical pneumatic bag or membrane which is inflated by compressed air or even water.
Pneumatic press (Willmes) advantages
even at low pressure, good liquid extraction, higher quality; gentle break up of pomace reduce extraction of bitter phenolics
Pneumatic press (Willmes) disadvatages
press cycle is slighty longer than horizontal screw press
This press is a variant of pneumatic press which can be pre flushed with inert gas, preventing oxygen exposure
The tank press
The tank press advantages
oxygen contact with luquid is eliminated, low pressure, gentle breaking of pomace, high quality juice
The tank press disadvantages
press cycle is longer than pneumatic press, most expensive type of press
All other presses are batch-process machines, which is labour intensive and time consuming. This press is used to process large quantities of grapes.
The continuous screw press
The continuous screw press consist of
perforated drum, with Archimedes screw inside
The continuous screw press advantages
very high output
The continuous screw press disadvantages
quality is not as good as in the batch-process
Colorless, highly toxic gas, produced in small quantities (about 10 mg/L) by yeast during fermentation
Sulfur dioxide (SO2)
Sulfur dioxide (SO2) has 4 properties in winemaking
-antiseptic. inhibits development of microorganisms -antioxidant. comines with oxygen, removing it before harm can be done -antioxidasic. denatures oxidasic enzymes such as tyrosinase -combines with acetaldehyde (by product of oxidation)
Sulfur dioxide (SO2) is added in wineries in one of four forms
-potassium metabisulfite powder. - pure SO2 gas compressed into liquid form - dissoved in solution (normaly 5%) - burning sulfur tablets or candles (for cleaning barrels)
Potassium metabisulfite powder
when dissolved in acid solution release sulfur dioxide. due to health reasons not longer permitted to use
SO2 is often added to juice before fermentation to control microbial activity and oxidation. (also added to grapes on way to winery) What is quantity used
for white must 60 - 100 mg/l for red must 10 - 60 mg/l Powdered form is used
Levels of added SO2 can be increased according to style of the wine because
if priority is to preserve primary aromas
Levels of added SO2 can be increased according to health of the grapes because
if rot is present you need to increase SO2
Levels of added SO2 can be increased according to pH level because
wines with higher pH need more SO2 cause less is in active form
What is a Free SO2
active, has protective properties. only molecular SO2 has any protective properties. it exists in more than one form in wine. portion dissolves in water to form sulfuruous acid, which is pH dependent. the other part remains as active molecular SO2. lower pH higher proportion remains as molecular SO2
What is a Bound SO2
has combined with various components such as sugars, aldehydes and ketones. it is inactive
What is a total SO2
sum of Bound SO2 and Free SO2
What is a maximum permitted SO2 level in dry red wines
limit of 150 mg/l. natural anti-oxidants are present
What is a maximum permitted SO2 level in dry white wines
limit of 200 mg/l
What is a maximum permitted SO2 level in sweet wines
limit of 250 mg/l for off-dry white with 5 g/l RS up to 390 mg/l for beerenauslese/TBA, Sauternes, etc. higher levels due to binding powers of sugars.
What is objective of pre-fermentation clarification in production of white and rose wines
to remove any solid particles suspended in must to produce cleaner flavors with more finesse and less bitternes
How much clarification is needed for production of complex white wines
little clarification
How much clarification is needed for production of delicate, highly aromatic white wines
lot of clarification
What is benefits of using cold settling
it is simple, effective, natural by gravity. produce highest quality grape must. overnight, cool temp. (5-10 C), clear must racked off the sediment
What is a purpose of adding pectolytic enzymes to the must during cold settling
they will destroy pectins which are responsible for holding particles of grape flesh in suspension
What is a centrifugation
pre-fermentation clarification separating the solids by centrifugal force at high speeds
What is diatomaceous earth filtration
pre-fermentation clarification which achieves highly clarified must, particularly suitable for aromatic varieties.
What is a flotation
pre-fermentation clarification. bubbling small amounts of nitrogen, carbon dioxide or air through cloudy grape must from the bottom of the vat, used on large volume of wine. when air is used - hyperoxidation at same time
What are advantages of centrifugation
high level of clarity, used in big wineries
What are disadvantages of centrifugation
harsh technique, high risk of oxidation, expensive process
What is disadvantage of diatomaceous earth filtration
it achieves highly clarified must but complete removal of solids can reduce nutrional content of must that yeast may struggle to ferment the sugars present
Name four ways of achieving pre-fermentation clarification in production of white and rose wines
cold settling centrifugation diatomaceous earth filtration flotation
Practice of adding sugar to grape must in order to increase potential alcoholic strength of wine is called
enrichment
Enrichment is done by adding
sucrose (beet or cane sugar) - chaptalisation concentrated unfermented grape juice use of sucrose is preferred, most neutral, cheapest, each kg increase wine volume by 0.63 kg.
How much sugar is need to raise ABV by 1%
for white wine: 17 g/l to raise ABV by 1% for red wine: 19 g/l to raise ABV by 1% - higher level of evaporation at higher temp. of fermentation and in pumping over
What is natural alcohol
total alcohol in un-riched must or wine
This must concentration technique involves evaporating must under vacuum, water evaporates at 20 C, low temperature minimises loss of aromatic and flavor potential
Vacuum evaporation
This must concentration technique is actually a filtration which take adventages of differences in molecular weight
Reverse osmosis. Concentrates flavors, acids, tannins.
This must concentration technique replicates naturally frozen grapes on vine
Cryoextraction. controversial
What must concentration technique can be used to remove alcohol and high levels of volatile acidity in finished wine
Reverse osmosis.
De-acidification
Total acidity can not be reduced by more than 1 g/l, expressed as tartaric acid. malic acid (harsher of the two) levels fall more rapidly then tartaric during grape ripening, so high levels in cool climates where double-salt is justified. in most ripe grapes tartaric is the main acid so adjustments are made using carbonate salts.
De-acidification using potassium bicarbonate
adition of potassium biacarbonate to must post-clarification but before alcoholic fermentation. this is preffered method of de-acidification. potassium batartrate crystals are formed. remove only tartaric acid.
De-acidification using calcium carbonate
high level of calcium tartrate form, leaving juice tartrate unstable until all crystals have been deposited. remove only tartaric acid.
De-acidification using double salt
adding calcium carbonate with small amount of calcium tartrate-malate (brand name Acidex) remove both tartaric and malic acids as crystals of calcium tartrate-malate are formed, which are insoluble.
De-acidification using malolactic fermentation
reduce only malic acid.
Natural de-acidification
through tartrate deposition after alcoholic fermentation.
De-acidification correlation with pH
De-acidification increases pH, which increase risk of microbial infection and decrease effectiveness of SO2
Acidification
decreases the pH of grape must or wine, which increases effectiveness of sulfur dioxide and inhibits the growth of bacteria. increasing levels of potassium salts can cause a decrease in pH even if titratable acidity is unchanged.
Correlation between pH and color of red wines
in red wines pH affects the color of pigmented tannins low pH wines appear brighter, more blue/purple high pH wines appear duller, more garnet/brown
Legal limits for acidification in EU
tartaric acid is used for acidification, add before fermentation legal limits 1.5 g/l in musts, 2.5 g/l in wines. limited to warmest zones CII and CIII
Adding of citric acid to wine
it increase wine stability. never before fermentation, it can be metabolised by yeast and bacteria to form acetic acid, thus increasing volatile acidity. EU limit of total citric acid in wine is 1 g/l
Adding tannins to wine
always prior to fermentation, can provide some protection from oxidation, can stabilise color, improve mouth feel
Adding bentonite
form of clay, used as fining agent in white winemaking, removes dissolved proteins. it is non selective, also remove flavor compounds.
Benefits of flavor and color enhancing enzymes
aid juice extraction optimise extraction of aroma precursors improve color extraction increase efficiency of settling They are added at crushing operations
From what source have enzyme preparations been developed
from a diverse species of fungi (aspergillus, rhizopus and trichoderma)
Oxygen
colorless, odourless gas, makes 1/5 of Earth atmosphere small amount during fruit processing is essential for development of yeast at start of fermentation
What is result of larger oxygen exposure during fruit processing
can lead to oxidation of phenolics, causing browning in white musts, and loss of primary aroma compounds in both color musts. activity of two oxidases-enzymes that catalyse oxidation must be restricted: laccase and tyrosinase
Laccase (oxidases-enzyme)
found in fruit affected by high levels of grey rot, responsible for more serious permanent browning of grape musts and wines and loss of aromatics
Tyrosinase (oxidases-enzyme)
found in healthy grapes. controlled by adding SO2.
Laccase (oxidases-enzyme) solution
resistant to SO2. pasteurisation (heating must to 65-70 C) but primary aromas and flavors also destroyed.
What are inorganic oxidasic catalysts
include many metal ions, especially copper. for this reason copper and bronze are avoided in modern winery equipment
Reductive or Anaerobic handling
minimise exposure to oxygen. SO2 is used during grape processing, temperatures are kept low, inert gases are used to flush out presses, pipes, vats.
Why black grapes are less vulnerable to oxidation
because greater concentration of tannins and pigments.
When is controlled oxygen exposure justified
for some varieties, such as chardonnay, controlled oxygen exposure prior to fermentation can lead to development of more complex aromas and flavors
What is hyperoxidation
process where enzymatic oxidation of phenolics is encouraged, converting them to insoluble polymers which may be removed by clarification treatments and resulting wine is more stable.
Name some possible negative changes due to excessive oxygen exposure
production of high level of acetaldehyde (ethanol) - flat sherry like flavor creation of bitter-tasting components from the oxidation of phenolics development of spoilage bacteria such as acetic bacteria.
