674 M. Dubernet
Table 12.2Indirect methods of determination in oenology by near IR analysers
Intra-laboratory Inter-laboratory
Method Measurement scale reproducibility reproducibility
Density 0.0012–1.40g/cm−−^3 0.00015 g/cm^3 0.0010 g/cm^3
Alcoholic volume 8–16vol.% 0.10vol.% 0.21vol.%
Titratable acidity 3–33g/L as tartaric
acid
0.11 g/L as tartaric
acid0.15 g/L as tartaric
acid
Volatile acidity 0.30–0.96g/L asacetic
acid
0.036 g/L as acetic
acid0.12 g/L as acetic
acid
PH 2.6–4.7 0.06 0.12
Potassium 600–8000 mg/L 10%
Total polyphenol index 15–100 14
Ammoniacal nitrogen 5–250 mg/L 16%
α-Amino nitrogen 5–250 mg/L 10%
Botrytis Cinerea Index of Musts
When this parasite invades the grape-berry, it leaves a characteristic metabolic foot-
print which has been shown to be closely correlated with the degree of infection
and the associated technological problems. Although the correlation is not linear it
may nonetheless be modelled using neural networks and thus it is quite possible to
express the degree of Botrytis infection in the form of an index.
The Fermentation Index of Musts
The fermentation activity of grapes or musts, which for example may start during
transport from the vineyard to the cellar, may be determined by an index that mea-
sures the organic compounds metabolised during fermentation.
Acetobacter Index
Acetobacterattack of grapes results in acid rot which has serious consequences in
terms of harvest quality. The level ofAcetobacterattack is determined by indices
that measure the compounds produced by this micro-organism.
Aspergillus Carbonarius in Musts
This fungal parasite is responsible for the production of ochratoxin A (OTA), the
presence of which is identified by the determination of related compounds.
The Determination of Ochratoxin A (OTA) in Wines
OTA is an organic compound that does have IR absorbance; however, it is present
in concentrations (some g/L) that are too low to permit its direct determina-
tion. In this particular case it has been demonstrated thatAspergillus carbonarius,
the organism responsible for the production of OTA, also produces other organic