Showing posts from May, 2018

The use of chitosan as an alternative to bentonite fining

By Karien O'Kennedy
The aims of the study were to investigate if chitosan can modify wine haze potential in a similar manner as bentonite, as well as if such fining will have an effect on wine chemistry. The haze-forming proteins in wine comprise of chitinsases, thaumatin-like (TL) proteins and beta-glucananses. Various factors in wine can influence haze forming including pH, ionic strength, alcohol concentration, polysaccharide and polyphenol concentrations, as well as the presence of sulphates. Usually bentonite is used as fining agent to remove potential haze-forming proteins, but bentonite can also remove certain aroma compounds, having a negative effect on wine quality. Chitin is able to remove chitinases, however, it is not permitted for use in winemaking. Chitosan, a derivative of chitin, is allowed. Currently it has been approved for use in winemaking by the OIV with the main purpose of controlling Brettanomyces spoilage.
Experimental layout Wine samples were obtained from …

Elevated temperatures affect flowering and fruit set

Aim: To investigate whether timing and duration of exposure to elevated temperatures impact the reproductive development of field-grown Shiraz grapevines.
Methods and results: The reproductive responses of Shiraz grapevines (Vitis vinifera L.) to two levels of elevated temperatures at budburst and flowering were investigated in an irrigated vineyard in the Barossa Valley (South Australia) over two consecutive growing seasons. Custom-built under-vine ‘tents’ and closed flow-through chambers enclosing a set of grapevines in the field were used to raise canopy temperatures above ambient. Higher temperatures at flowering resulted in lower yields due to decreased fruit set in 2007-08, while yield was virtually unaltered the following year despite the lower fruit set. Two indicators of grapevine reproductive performance, Coulure Index and Millerandage Index that quantify abscised and underdeveloped berries, respectively, were calculated to be higher as a result of the heat treatments in both…

Resilience of grapevine yield in response to warming

Aim: To evaluate the effect of elevated temperature on the yield of Shiraz vines in the Barossa Valley of Australia.
Methods and results: The researchers compiled and analysed 37 pair-wise yield comparisons between heated and control vines spaning seven consecutive vintages from 2009-10. Heating with open-top chambers increased daily average temperature by approx. 2 °C above ambient in realistic vineyard conditions, in comparison to 0.9 to 2.9 °C projected warming for south-eastern Australia (2030-2070). The combination of seasons, varieties, fruit loads, pruning times, and water regimes returned an 8.5-fold variation in the yield of unheated vines. Warming had no statistically significant effect on yield in 32 out of 37 comparisons, reduced yield in 2 and increased yield in 3.
Conclusion: Projected warming is unlikely to cause widespread reduction of yield in environments with thermal regimes similar to Barossa Valley; extrapolation to cooler or warmer regions is not warranted.

Magnetic polymers for the reduction of pyrazines in wines

By Karien O'Kennedy
A new remediation method for wines with elevated IBMP levels has been trialled using magnetic polymers, prepared in the same way as ordinary polymers but with the incorporation of iron oxide nanoparticles as magnetic substrates. Magnetic polymers were found to have removed over 40% of the IBMP present in spiked model wine and white wine within ten minutes.
Alkylmethoxypyrazines (MPs) are aroma volatiles noted for their potency and ability to impart sensory characters of green bell pepper, grass, and vegetables to wine. Three grape-derived MPs have been uncovered in recent decades—3-isobutyl-2-methoxypyrazine (IBMP), 3-isopropyl-2-methoxypyrazine (IPMP) and 3-sec-butyl-2-methoxypyrazine (SBMP) —that are mainly located in grape stems, followed by skins and seeds. Another source of MPs in wines originates from the contamination of grapes by Coccinellidae beetles, leading to a wine fault known as ‘ladybug taint’ (LBT). More recently, 2.5-dimethyl-3-methoxypyrazine (…