15.4 Faults Flashcards
Name several process that are carried out during the production process to protect against faults.
- sorting to exclude damaged or mouldy fruit
- exclusion of oxygen at key points in the process
- temperature control
- scrupulous hygiene in wineries
- stabilisation
- final adjustment of SO2
- fining and filtering
- care over bottling
Why might wines be cloudy or hazy?
- growth of yeast or bacteria
- failure to filter adequately (e.g. pumping wine at too high a pressure through a depth filter so that some unwanted molecules go through the filter)
- unstable proteins remaining in the wine, causing it to go hazy after the wine has left the winery
- protein haze where fining is not effective
- wrong type of fining agent has been used
- wine has been over-fined
How can a winemaker prevent cloudiness and haziness?
- better hygiene in the winery
- pre-bottling chemical analysis
- filtering wine to remove yeast or bacteria before bottling
- fine correctly and conduct analysis after fining
What are tartrates?
Colourless or white crystals in the bottom of bottle that can be mistaken for fragments of glass
- can be seen as a fault by consumers
- knowledgeable drinkers know that this is a natural process triggered by low temperatures and is completely harmless to health and wine quality
How can tartrates be prevented? In what types of wines is this typically done?
- inexpensive and mid-priced wines
- stabilised before release from the winery
Why may visible bubbles or spritz in wine be seen as a fault?
- If accompanied by cloudiness, it would indicate unwanted re-fermentation in the bottle (shows a failure to stabilise and clarify/filter the wine adequately)
In what types of wines would visible bubbles or spritz not be considered a fault?
- Wines that purposely include a low level of spritz
(e. g. Muscadet sur lie or Vinho Verde). - Some inexpensive and mid-priced white wines will have a small amount of CO2 added before bottling to preserve and enhance freshness.
What is the effect of cork taint on the wine?
- Associated with a very unattractive, mouldy, wet cardboard smell
- Reduces the fruit character
- Shortens the finish
What is oxidation (fault)?
Excessive exposure to oxygen either in the winemaking process or once in bottle or other container
What can cause oxidation post bottling?
- faulty bottling
- poor quality corks or plastic closures
- simply keeping wine for too long if it is not of a quality to age
Describe an oxidized wine (fault).
- wine becomes prematurely brown in colour
- loss of primary fruit
- vinegary smell
What is volatile acidity?
- All wines have volatile acidity
- Excessive amounts give a pungent smell of nail varnish and/or vinegar
What causes volatile acidity?
- activity of acetic acid bacteria
- inadequate levels of SO2
- excess exposure to oxygen
What can reduce the threat of volatile acidity?
- sorting fruit to exclude damaged grapes
- scrupulous hygiene in the winery
- keeping vessels topped up
- careful racking (to avoid excessive exposure to oxygen)
- maintaining adequate SO2 levels
What is reduction?
- associated with sulfur-like odours that range from onion to rotten eggs
- caused by high levels of volatile, reductive sulfur compounds
- depending on compounds present and levels, can add a layer of complexity or can be considered a fault
Name 3 causes of reduction.
- Sulfur compounds can be produced by yeast under stress (due to low nitrogen levels) in the winemaking phase
- Near complete exclusion of oxygen during ageing in closed vessels, especially when lees ageing
- When wine is closed with the impermeable type of screw cap
How can reduction be avoided?
- ensuring yeast has sufficient nutrients and oxygen
- ensuring must is at an adequate temperature
- reducing SO2 levels (especially if the closure used allows very little oxygen ingress)
What is light strike?
- caused by UV radiation and certain wavelengths of visible light reacting with certain compounds in the wine to form volatile sulfur compounds
- gives odours such as dirty drains
What wines are most at risk for light strike?
- Wines that are left in direct sunlight
- Wines placed near fluorescent lighting (e.g. in retailers)
- Wines packages in clear glass
What is Brettanomyces?
- Yeast produces a range of off-aromas from animal, spicy or farmyard smells
- Fruity flavours are reduced
- Acidity/tannins become more prominent
- Can add complexity to red wines at low levels
What faults can also be considered positive at low levels?
- Brettanomyces
- Reduction
- Volatile Acidity
What are the keys ways to avoid Brettanomyces?
1 .excellent hygiene
- maintaining effective SO2 levels
- keeping pH levels low
- keeping the period between the end of alcoholic fermentation and malolactic conversion as short as possible so that SO2 can be added as soon as possible
Why is Brettanomyces typically difficult to get rid of?
Once it has occurred in a winery, Brettanomyces is difficult to eradicate, especially as wood can host the organism and be very difficult to clean effectively. It can be present in old or new barrels.
