Multispectral imaging is capable of discriminating MOG (material other than grapes) and Botrytis-infected grapes in samples from mechanically harvested grape loads, a recently completed Wine Australia-funded study has found.
The findings are important, because being able to identify and manage contaminants and MOG at the weighbridge is a critical step in managing overall fruit quality and wine.
‘Leaves and petioles collected as part of grape harvest and disease-affected fruit have the potential to impact on wine quality when they are included in the ferment’, said principal investigator Dr Paul Petrie, who undertook the research while at the Australian Wine Research Institute.
‘High MOG levels can lead to undesirable impacts on wine flavour and aroma. Disease, especially Botrytis, contains enzymes that can lead to rapid oxidation of the juice and wine – markedly reducing its quality and turning the wine brown.’
Currently, MOG within mechanically harvested fruit is assessed using a visual rating system – ‘so there is always room for conjecture around the accuracy of the MOG assessment’, said Dr Petrie.
And while chemical analysis methods have been trialled to quantify the level of Botrytis in fruit, Dr Petrie say these methods are often not precise at the low concentrations where Botrytis can have an effect – and samples take some time to be collected and analysed.
‘The imaging system we have developed, however, helps to overcome these issues – with the added benefit of rapid assessment and analysis.’
The team initially used hyperspectral imaging with a full spectral linescan camera to assess both laboratory-infected Botrytis samples and field samples.
Eight wavelengths were then selected for use with a filter-based multispectral camera. This system was selected because it was more applicable for use at the winery weighbridge.
What the research team found was encouraging: spectral imaging was not only able to identify Botrytis infection and MOG, but could also differentiate types of fungal infection, along with grape sunburn and shrivel.
The study found:
- Hyperspectral imaging (HSI) could discriminate between clean and infected red and white grapes. The calibrations worked across growing regions, grape varieties and Botrytis sources.
- The multispectral camera system was able to quantify the amount of MOG and Botrytis-affected fruit that was added to samples collected at the weighbridge. This proof of concept supports the development of commercial systems to monitor loads when they are delivered to the winery.
- HSI could also discriminate Botrytis infection from sour rot (mixed fungal and bacterial infection of grapes). Washing sporulating berries with grape juice or smashing berries, to simulate mechanical harvesting, did not prevent identification of Botrytis.
- HSI could identify sunburn in white grapes and shrivel in red and white grapes; and discriminate other grapevine components that often form MOG in mechanically harvested grape loads (i.e. canes, wood, petioles, leaves and insects).
‘The findings are exciting, because having an objective system to measure Botrytis bunch rot and MOG will provide greater transparency of the assessment process and help prevent the production of poor quality wine’, said Dr Petrie.
This project was funded by the Australian Government Department of Agriculture, Water and the Environment as part of its Rural R&D for Profit program and Wine Australia, in partnership with the AWRI.