Protein haze formation
Background
Preventing protein haze is a major challenge in white wine production. The current method of bentonite fining is effective, but has disadvantages associated with both efficiency cost and sustainability of winery operations. This research project explores ways to improve bentonite efficiency by improving the ways wineries estimate the dose of bentonite required. In addition, we are working towards a more thorough understanding of the phenomenon of haze formation.
Progress
One way of increasing bentonite efficiency is to improve the way wineries determine the amount of bentonite required to prevent subsequent protein haze formation. We have examined the suitability of the current tests used by Australian winemakers to predict wine protein instability (80ºC for six hours, 80°C for two hours and Bentotest) through long-term storage trials of wines that had been fined according to the test results. We challenged the wines to severe transport and storage conditions and also held them under best practice cellar conditions. Under the severe conditions, none of the wines became hazy. Under the best practice conditions some of the wines eventually became slightly hazy but only after more than two years of storage. Such slight hazes would probably be commercially acceptable. This means that fining according to the rates determined by all the tests examined by us would most likely prevent haze in the bottle. It was significant, however, that the tests gave different bentonite fining rates, hence, using some of the tests could lead to over fining with bentonite.
We have also screened more than 200 commercial white wines for protein stability under simulated severe transport and storage conditions. Only one wine failed this test. This wine also failed both heat tests at 80ºC for two or six hours. These data confirm that the vast majority of Australian commercial white and rosé wines are protein stable. The wines screened included a subset of wines from companies that use the 80ºC for two hour test and all these wines were stable. This also confirms our data that bentonite fining according to the rates determined by testing at 80°C for two hours would most likely prevent haze formation in the bottle in practice.
One approach we have taken recently to further elucidate the mechanism of haze formation is to develop a mathematical model describing the process of protein aggregation. This model suggests that the protein aggregates are initially spherical and then develop more of an oblate deformation eventually leading to a more cylindrical shape. Being able to define particle size and shape is important because these parameters affect light scattering and thus the turbidity of solutions containing these particles. By having a greater knowledge of the haze formation process on a molecular level, such as the size and shape of the interacting protein aggregates, we will be more successful in proposing alternative solutions to the wine haze problem.
Highlights
- Bentonite fining rates can be reduced by using a heat test of 80oC for 2 hours without compromising wine stability
Project leader: Dr Liz Waters
Project team members:
Publications:
858 Waters, E.J.; Alexander, G.; Muhlack, R.; Pocock, K.F.; Colby, C.; O’Neill, B.K.; Høj, P.B.; Jones, P. Preventing protein haze in bottled white wine. Aust. J. Grape Wine Res. 11: 215–225; 2005 (click here to order).
956 Pocock, K.F.; Alexander, G.M.; Hayasaka, Y.; Jones, P.R.; Waters, E.J. Sulfate – a candidate for the missing essential factor that is required for the formation of protein haze in white wine. J. Agric. Food Chem. 55: 1799–1807; 2006 (click here to order).
1004 Pocock, K.F.; Waters, E.J.; van Sluyter, S.; Macintyre, O.J.; Schmidt, S.A.; Herderich, M.J.; Pretorius, I.S. How well does your lab test predict protein stability during storage and transport? Aust. N.Z. Wine Ind. J. 22(2), 21–23; 2007 (click here to order).
1056 Pocock, K.F., Waters, E.J., Herderich, M.J., Pretorius, I.S. Protein stability tests and their effectiveness in predicting protein stability during storage and transport. Aust. N.Z. Wine Ind. J. 23(2), 40–44; 2008 (click here to order).
Additional links
- Commercial Services - Analyses: Stability analysis and fining trials
- Industry Support - Hazes and deposits (login required)
- Marangon et al, 2009. Crystallization and preliminary X-ray diffraction studies of four thaumatin-like protein isoforms from Vitis vinifera grape juice - Winner, Best Poster Prize, In Vino Analytica Scientia (Angers, France) 2009 (PDF, 1.8mb)