All kits use absorbance spectroscopy, which works within a linear concentration range. When absorbance approaches 1.8 AU, results become non-linear and signal is lost in noise — meaning dilution is required.
During vintage, analytes such as:
May exceed the measurable range.
General guidance:
Red wines rarely need decolourisation. PVPP can be used if required, but dilution is usually sufficient.
Grape juice, ferments and finished wines can all be tested — with correct preparation.
This transcript has been lightly edited for readability and to correct obvious automatic-caption errors. Product and method information should be checked against current Vintessential documents before use.
0:01 Depening on the stage of production, some samples may need to be diluted. During harvest, malic acid, glucose, fructose, primary amino nitrogen and ammonia may be present at concentrations above the kit's measurement range.
0:16 Vintessential kits use absorbance spectroscopy, which is linear over a defined concentration range. At higher concentrations the response becomes nonlinear. When an Absorbance One reading approaches 1.8 absorbance units, the sample needs to be diluted because the analytical signal can be lost in noise.
0:51 A fact sheet on the Vintessential website provides suggested dilutions and workable ranges for each kit.
0:58 The appropriate dilution depends on the stage of production. For the Malic Acid Test Kit, the demonstration recommends a sample concentration below 0.4 g/L in the cuvette.
1:11 During vintage, a 1 in 20 or 1 in 10 dilution may be appropriate. A finished wine may require only a 1 in 2 dilution.
1:19 Most wines do not need to be decolourised. PVPP can be used to reduce strong red colour and assist the spectroscopic measurement without affecting the analyte or malic acid concentration.
1:40 If a red wine is already being diluted 1 in 5 to bring its concentration below 0.4 g/L, it generally does not also need to be decolourised.
1:56 Other sample preparation options include centrifugation or filtration during vintage. This is not always necessary because the sample volume is small compared with the buffers and other reagents. Very thick grape samples are more likely to require additional preparation.
2:22 Absorbance One and Vintessential test kits can be used with samples ranging from grapes and grape juice through to ferments and finished wines.
2:31 For a portable workflow in a vineyard or at a site without a centrifuge, folding filter paper can provide another sample preparation option.
