Ella Robinson

Degradation of white wine haze proteins by Aspergillopepsin I and II during juice flash pasteurization

Bentonite is commonly used to remove grape proteins responsible for haze formation in white wines. Proteases potentially represent an alternative to bentonite, but so far none has shown satisfactory activity under winemaking conditions. A promising candidate is AGP, a mixture of Aspergillopepsins I and II.; a food grade, well characterized and inexpensive protease, active at wine pH and at high temperatures (60-80°C). AGP was added to two clarified grape juices with and without heat treatments (75°C, 1min) prior to fermentation. AGP showed some activity at fermentation temperatures (≈20% total protein reduction compared to control wine) and excellent activity when combined with juice heating (≈90% total protein reduction). The more heat stable grape proteins, i.e. those not contributing to wine hazing, were not affected by the treatments and therefore accounted for the remaining 10% of protein still in solution after the treatments. The main physicochemical parameters and sensorial characteristics of wines produced with AGP were not different from controls.

Comparison of extraction protocols to determine differences in wine-extractable tannin and anthocyanin in Vitis vinifera L. cv. Shiraz and Cabernet Sauvignon grapes.

Cabernet Sauvignon and Shiraz grapes were sourced from different regions within Australia, and microvinified with a skin contact period of 6 days. Grape samples were extracted using two protocols: a 15% v/v ethanol, 10 g/L tartaric acid extract of gently crushed berries (wine-like, WL) and a 50% v/v ethanol, pH 2 extract of grape berry homogenate. It was found that in WL extracts, grape tannin and anthocyanin concentrations were strongly related to wine tannin, anthocyanin and color density achieved during the skin contact period. No relationship was observed for grape tannin concentration analyzed in homogenate extracts and wine tannin, but a strong, positive relationship was found for anthocyanin concentration. When the data obtained from homogenate extraction was treated separately by grape variety, a stronger relationship between grape and wine tannin concentration was observed. Tannin compositional analysis in wines indicated that higher tannin concentrations were due to the extraction of tannin of higher molecular mass during fermentation, most likely from grape skins.

R&D in action in Australia: non-destructive analysis of wine

10 Introduction S pectroscopic analytical techniques are becoming increasingly important in grape and wine analysis. Such techniques offer significant advantages over traditional laboratory methods in their speed and ability to measure multiple analytes simultaneously. Examples common in Australian wine laboratories include: near infrared (NIR) instruments used for measuring alcohol, Fourier transform infrared (Ft-IR) instruments developed specifically for routine wine composition analysis and ultraviolet/visible (UV/vis) instruments used in a wide range of methods. An ideal method for the determination of wine chemical composition in a routine manufacturing schedule should be noninvasive, non-destructive and rapid in order to ensure timely processing of the product being analysed. In the shorter wavelength region of the NIR spectral range (700–1600 nm), spectra exhibit low intensity absorbance peaks and can therefore cope with longer sample path lengths (5–30 mm) but have poor spectral resolution; peaks at longer wavelengths (>1500 nm) have greater absorbance intensities and require short optical path lengths but provide better spectral resolution. Glass is transparent to NIR radiation—a property that has allowed the pharmaceutical industry to use NIR for direct analysis of liquids in intact glass vials in order to determine moisture in lyophilised sucrose as well as for real-time monitoring of solid phase synthesis of a resin bound to alcohol. the use of NIR spectroscopy for analysis of foods and beverages such as Sufu, beer and whisky, non-destructively at their point-of-sale has also been reported by other authors. After intensive R&D work at the Australian Wine Research Institute (AWRI) in 2010, the BevScan (Figure 1), a new vis-NIR instrument developed in a partnership between Jeffress Engineering Pty Ltd (www.jeffress.com.au) and the AWRI, takes the advantages of rapid spectral methods a big step further by allowing analysis of wine through an unopened bottle. the ability to analyse bottled wine non-destructively for the first time offers up a huge range of potential applications never before accessible to the wine sector. the BevScan additionally provides a cuvette attachment, which gives users the flexibility to also use it as a conventional vis-NIR instrument. this type of instruments or sample presentation can be used only as an indicative rather than a quantitative analytical tool to, for instance, monitor a process because of limitations in analytical accuracy. It is expected that future applications development will provide the wine industry with a very fast and non-destructive method to monitor composition or detect changes, i.e. to identity unwanted problems in bottled wine prior to retail sale (e.g. oxidation) and provide a rapid means of qualitative rather than quantitative analysis.