This project will investigate:
- the compositional drivers for texture, hotness and bitterness;
- the role of macromolecules such as tannins, polysaccharides, proteins and their aggregate colloids in the expression of texture, stability, clarity and filterability, the source of these molecules or their precursors and the impact of winemaking processes on their retention and/or transformation;
- practical methods for wineries to determine likely extractability of macromolecules during winemaking;
- alternative strategies for achieving protein stability and strategies for the stabilisation of colour independent of vintage effects.
The molecular drivers for attributes such as texture, bitterness and hotness in wines are poorly understood. Texture is considered a key differentiator in the value proposition for many wines. The ability to modulate this and other non-volatile wine sensory characteristics poses a significant opportunity for increasing the price point of wine in the marketplace.
Macromolecules such as tannins, polysaccharides and proteins, both in their molecular form and aggregated together as colloids, are major wine components which also have a significant impact on wine stability, clarity and filterability. For example, macromolecules form the basis of heat instability and hazes associated with metal ions. They also form the basis of colour stability in the form of pigmented polymers of a range of phenolic compounds and as colloids have a significant impact on wine clarity. Finally, macromolecules and their colloidal forms can pose a significant barrier to the filtration process by fouling media and lowering efficiency, which can add substantial cost to the preparation of wines to a market-ready state.
Compounds responsible for taste and texture will be identified by isolating compounds, reconstituting them in model and real wines and creating wines with varied composition and analysing the impacts through sensory studies.
The plan to understand the impact of filtration and clarification on wine colloids involves lab-based studies on the influence on wine style of treatment with different factors influencing production and clarification of juice, followed by larger winemaking trials using the knowledge developed in the lab-based experiments.
Tools and knowledge to manage filterability will be developed by filtering wines in series to a range of appropriate filtration levels (from cross flow to finer levels such as 3.0, 1.0, 0.65, 0.45 µm), monitoring filtration efficiency and then monitoring effects on the wine composition during bottle storage for two years.
Tools and knowledge to manage colour and protein stability in wines will be developed though winemaking trials to characterise colour compounds and establish parameters governing colour stability; by using reconstitution experiments to understand the mechanisms for haze formation and through evaluating novel processes to stabilise wines against protein haze stability.
Macromolecule and colour extraction, stability and retention and its influence on wine style and production practices will being studied using small and large-lot winemaking to correlate characteristics in grapes relative to wines, establish practical assays for assessing grape extraction, and undertake advanced characterisation of grape chemistry and biochemistry.
The knowledge and tools generated by this project will allow winemakers to more objectively manage texture, stability, colour, clarity and filterability during winemaking.