15.4 Faults

Question 1

Name several process that are carried out during the production process to protect against faults.

Answer 1

• 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

Question 2

Why might wines be cloudy or hazy?

Answer 2

• 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

Question 3

How can a winemaker prevent cloudiness and haziness?

Answer 3

• 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

Question 4

What are tartrates?

Answer 4

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

Question 5

How can tartrates be prevented? In what types of wines is this typically done?

Answer 5

• inexpensive and mid-priced wines

- stabilised before release from the winery

Question 6

Why may visible bubbles or spritz in wine be seen as a fault?

Answer 6

• If accompanied by cloudiness, it would indicate unwanted re-fermentation in the bottle (shows a failure to stabilise and clarify/filter the wine adequately)

Question 7

In what types of wines would visible bubbles or spritz not be considered a fault?

Answer 7

• 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.

Question 8

What is the effect of cork taint on the wine?

Answer 8

• Associated with a very unattractive, mouldy, wet cardboard smell
• Reduces the fruit character
• Shortens the finish

Question 9

What is oxidation (fault)?

Answer 9

Excessive exposure to oxygen either in the winemaking process or once in bottle or other container

Question 10

What can cause oxidation post bottling?

Answer 10

• faulty bottling
• poor quality corks or plastic closures
• simply keeping wine for too long if it is not of a quality to age

Question 11

Describe an oxidized wine (fault).

Answer 11

• wine becomes prematurely brown in colour
• loss of primary fruit
• vinegary smell

Question 12

What is volatile acidity?

Answer 12

• All wines have volatile acidity

- Excessive amounts give a pungent smell of nail varnish and/or vinegar

Question 13

What causes volatile acidity?

Answer 13

• activity of acetic acid bacteria
• inadequate levels of SO2
• excess exposure to oxygen

Question 14

What can reduce the threat of volatile acidity?

Answer 14

• 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

Question 15

What is reduction?

Answer 15

• 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

Question 16

Name 3 causes of reduction.

Answer 16

1. Sulfur compounds can be produced by yeast under stress (due to low nitrogen levels) in the winemaking phase
2. Near complete exclusion of oxygen during ageing in closed vessels, especially when lees ageing
3. When wine is closed with the impermeable type of screw cap

Question 17

How can reduction be avoided?

Answer 17

• 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)

Question 18

What is light strike?

Answer 18

• 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

Question 19

What wines are most at risk for light strike?

Answer 19

• Wines that are left in direct sunlight
• Wines placed near fluorescent lighting (e.g. in retailers)
• Wines packages in clear glass

Question 20

What is Brettanomyces?

Answer 20

• 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

Question 21

What faults can also be considered positive at low levels?

Answer 21

1. Brettanomyces
2. Reduction
3. Volatile Acidity

Question 22

What are the keys ways to avoid Brettanomyces?

Answer 22

1 .excellent hygiene

2. maintaining effective SO2 levels
3. keeping pH levels low
4. 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

Question 23

Why is Brettanomyces typically difficult to get rid of?

Answer 23

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.