Measurement of heat stability of wine

Heat instability of wine is generally due to precipitation of unstable grape proteins. Most frequently, this is of interest in white table wines. Several test are available and a comparison of some of these is given by Toland et al. (1996). This document gives a brief summary of the procedures and equipment requirements for some commonly used techniques for determination of heat stability of wines.

Heat test

Description: A filtered wine sample is heated to 80C for six hours and then, after cooling, examined by eye against a light source for the presence of a haze in comparison with an untreated control sample of the filtered wine. Narrowing the focus of the light beam so as to give a cylindrical shaft of light of approximately 3 mm in diameter helps to illuminate suspended particles responsible for haze. A turbidimeter can be used for more objective comparison of the turbidity in the two samples. In this case, wines that exhibit a turbidity increase of greater than a given criterion for Nephelometer Turbidity Units (NTU) after heating, as compared with the unheated control, can be considered to have failed the heat stability test. Some laboratories use a criterion of 0.5 NTU, but other practitioners in industry have indicated that a more reasonable criterion is 2.0 NTU (Wilkes, personal communication 2004). Addition of 0.5 g/L of tannic acid makes the test more stringent in simulating cork contact (Rankine 1989). Further information about the heat test can be found here.

Equipment: Sample containers for wine samples (e.g. 25 mL screw capped glass tubes), light source, membrane filtration apparatus, turbidimeter (optional)
Reagents: none required
Services: Wash up area
Space required: Minimal bench space

BentoTest®

Description: This chemical test is rapid, does not require heating of the test samples and is considered to be more stringent than the heat test (Rankine 1989). The test uses phosphomolybdic acid reagent (5% phosphomolybdic acid, 5% sodium sulfate, 0.25 g/L glucose in 15% stock sulfuric acid in deionised water) to denature and precipitate proteins through the formation of cross-linkages with the molybdenum ion (Zoeklein et al. 1999). Add 1 mL of BentoTest reagent to 10 mL of wine and examine the solution by eye for the presence of haze. As in the case of the heat test, a turbidimeter can be used for more objective assessment of the turbidity in the sample.

Equipment: Test tubes, turbidimeter (optional)
Reagents: none required
Services: Wash up area
Space required: Minimal bench space

References and further reading

  • Iland, P.; Ewart, A.; Sitters, J.; Markides, A.; Bruer, N. (2000) Techniques for chemical analysis and quality monitoring during winemaking. Campbelltown, SA Patrick Iland Wine Promotions.
  • Pocock, K.F.; Rankine, B.C. (1973) Heat test for detecting protein instability in wine. Aust. Wine Brew. Spirit Rev. 91: 42-43.
  • Rankine, B.C. (1989) Making good wine. Melbourne, Vic: Macmillan Pty Ltd: 313.
  • Rankine, B.C.; Pocock, K.F. (1976) Wine stability tests for quality control. Aust. Wine Brew. Spirit Rev. 96(12): 24-25.
  • Toland, T.M.; Fugelsang, K.C.; Muller, C.J. (1996) Methods for estimating protein instability in white wines: a comparison. Amer. J. Enol. Vitic. 47(1): 111-112.
  • Zoecklein, B.W.; Fugelsang, K.C.; Gump, B.H.; Nury, F.S. (1999) Production Wine Analysis. New York: AVI Van Nostrand Reinhold: 469-473.
  • Wilkes, E. (2004) Technical Laboratory Manager, Beringer Blass Wine Estates, Nuriootpa SA, personal communication.