The heat stability test uses 30 mL of filtered sample heated to 80°C for six hours for rosé and red wines and two hours for white wines. A control sample is also prepared, but not heated. After the heating step, the sample is cooled according to the table below and viewed under a very strong light with a narrow aperture. If a beam of light is visible passing through the sample, it is considered a fail. Turbidity is also measured using nephelometry. The nominal pass point for stability is a turbidity difference of less than 0.5 units when compared with an unheated filtered control sample. There are many exceptions to this and it is always wise to perform a visual check of the samples. AWRI Commercial Services offers both checks to enable each client to make the most informed decision.
The heating and cooling times used are dependent on the wine matrix, as shown in the table below:
|Matrix||Heating time||Cooling time||Turbidity limit for pass|
|White wine||2 hours||3 hours||< 2 NTU|
|Rosé wine||6 hours||< 5 minutes*||< 0.5 NTU|
|Red wine||6 hours||< 5 minutes*||< 0.5 NTU|
*Rosé and red wines may be read as soon as they reach room temperature, which is at the end of the 5-minute automatic cooling cycle on the heat bath.
Commercial Services’ cold stability method uses 100 mL of filtered sample immersed in a -4°C liquid bath for 72 hours. The sample is then viewed under strong light to determine the presence or absence of crystals. The sample is assessed at cold and ambient temperatures as some phenolic material, ie amorphous pigments and tannins, may form a transient precipitate in some red wines. Allowing the sample to warm to ambient temperature usually results in their resolubilisation, and this allows precipitates to be differentiated from potassium bitartrate crystals.
We can also isolate and identify crystals, providing that there is sufficient precipitate to evaluate.
Bentonite fining trials
AWRI Commercial Services can conduct bentonite fining trials to determine the optimum bentonite addition for a wine, removing the risk of haze formation while minimising flavour loss. Clients provide their own bentonite to avoid any effects from brand and batch variation. Assistance is also provided in determining which fining rates to assess. All trials are measured by visual inspection (using the method described for heat stability) and turbidity meter.
|Prices per analysis|
|Analysis||Per Sample (excluding GST)||Volume required||Target response time|
|Heat stability||$24.15||100 mL||48 hrs|
|Cold stability||$24.15||200 mL||96 hrs|
|Stability package||$42.00||300 mL||96 hrs|
|Bentonite trial including three additions||$94.50||2 x 750 mL bottles
Bentonite required – 20 g
For more information, please contact AWRI Commercial Services on (08) 8313 6600 or e-mail firstname.lastname@example.org