acidity – see Chapter 7;
Lactic bacteria and Pediococcus related faults – see Chapter 11.
1.10.2.3 Minimising the Occurrence Microbiological Faults
The key tools in minimising the risk of the occurrence of microbiological faults are as follows.
In the vineyard:
Creating and maintaining open leaf canopies to help air‐flow;
Controlling pests such as European grapevine moth (Lobesia botrana), and vinegar fly (Drosophila melanogaster);
Preventing or controlling vine diseases such powdery mildew and downy mildew;
Preventing or controlling grape rots, such as Botrytis cinerea;
Picking only healthy and undamaged fruit;
Picking at an appropriate pH;
Harvesting as cool as possible and transporting to the winery without delay.
In the winery and cellar:
Sorting fruit to exclude rotten and damaged berries and materials other than grapes (MOGS);
Maintaining an appropriate pH in must and wine;
Scrupulous winery and cellar hygiene;
Using commercial preparations of S. cerevisiae for alcoholic fermentations and lactic acid bacteria strains for the MLF.
Careful oxygen management in wine – e.g. avoiding ullage in vats and barrels;
Controlled temperatures for fermentation, maturation, and storage;
Creating and maintaining a nutrient desert [22];
Controlled humidity in the winery (maximum 75%) and barrel store (maximum 80%);
Maintaining an appropriate level of molecular sulfur in wine.
1.10.3 Chemical Nature Faults
1.10.3.1 Examples of Chemical Faults
Chemical faults result from unwanted chemical changes in wine and may be due to internal or external factors. Two of the most common faults of chemical origin are chemical oxidation and, conversely, reduced aromas or reduction. There are thousands of chemical reactions that take place during the winemaking processes; some of these can result in the synthesis of compounds noted for their off‐odours and flavours, whilst others give simple changes, the impact of which may include immediate or rapid product deterioration.
Faults that are generally regarded as being primarily of a chemical nature include
Excessive acetaldehyde – see Chapter 5;
Chemical oxidation – see Chapter 5;
Reduced aromas/reduction – see Chapter 6;
Iron haze and copper haze – see Chapter 10;
Eucalyptol – 1,8‐cineole – see Chapter 12;
Smoke taint related compounds, including guaiacol, 4‐methyl‐guaiacol, 4‐methyl‐syringol, m‐cresol, o‐cresol, and p‐cresol – see Chapter 12;
Brown marmorated stink bug related compounds, including trans‐2‐decenal – see Chapter 13.
1.10.3.2 Minimising the Occurrence Chemical Faults
The key tools in minimising the risk of the occurrence of chemical faults are as follows.
In the vineyard:
Maintaining sufficient, but not excessive, soil nitrogen levels;
Discontinuing the use of all chemical contact and systemic treatments well before harvesting;
Avoiding using agrochemicals that may break down into unwanted odours compounds such as 2,4‐dichlorophenol and store all agrochemicals away from possible sources of contamination;
Minimising sources of aerial pollution, including the burning of winery rubbish;
Minimising the vineyard presence of pests, particularly ladybug (Coccinellidae) and brown marmorated stink bug (Halyomorpha halys).
In the winery and cellar:
Careful oxygen management – e.g. avoiding ullage in vats and barrels and using gases to sparge equipment, but ensuring that adequate levels of dissolved oxygen are maintained;
Avoiding pick‐up of metals, particularly copper and iron – these metals can be contaminate wine from inappropriate or damaged equipment, particularly valves and fittings;
Maintaining adequate levels of molecular SO2 in wine;
Avoiding possible contact with sources of chemical contamination, e.g. damaged tank linings.
1.10.4 Physical Faults, Contamination, and Packaging Damage
Some physical faults are as a result of chemical or microbiological factors. Packaging damage or failure, sometimes due to poor storage conditions, can have devastating consequences. By way of a very simple example, a loss of bubbles (probably accompanied by oxidation) in a Champagne or other sparkling wine due to shrinkage or other failure of the cork closure would be regarded as a most serious fault. In fact a cork ‘champagne’ stopper does not provide a complete hermetic seal. Some 30% of CO2 may be lost in Champagne aged for 75 months at 12 °C (less in the case of magnum [1.5 l] bottles and more in the case of half [37.5 cl] bottles) [23]. Wine may be contaminated with a variety of objects, including flies and other insects, pieces of metal, filter materials, and oil. Whilst some of the contaminants are likely to affect bottles on an individual basis, others may require the recall of an entire batch. Occasionally pieces of glass may enter the bottle, due to problems with filling heads, the jaws of the corking or closure unit, or bottle manufacture. Wine may also become contaminated with paint, resins (including epoxy resin), brine, glycol, metals, and other substances due to damage in tanks, pipes, hoses, or other production equipment. Physical faults, physical contamination, and packaging damage are issues that
