Sorting Tables: Hand Sorting vs. Optical Sorters

Sorting is a quality step at the winery. Freshly picked grapes entering the winery have to be sorted for quality. Sorters are devices that remove further vegetal matter (stem fragments, petioles and leaves), other contaminants such as insects, or undesirable grapes and parts of grapes, such as diseased or unripe grapes. Matter other than grapes (MOG) is the non-grape material that finds its way into picking crates or bins, whether grapes are hand-picked or machine harvested.

• MOG can include leaves, petioles and canes, as well as stones, sticks, strainer wire, caterpillars, millipedes and stink bugs
• Hand sorting is typically done on conveying tables that spread the grapes and present them to the people sorting; belt conveyor tables and vibrating conveyor tables are both used
• An optical sorter recognises anything that does not have the desired size, shape and colour and blows it onto another conveyor belt with a blast of air
• Mechanical harvesters still cannot distinguish as well as humans between ripe, underripe or rotten grapes, leaves, dirt and bugs, which increases the need to sort machine-harvested fruit

On a hand-sorting line, the grapes usually travel down a conveyor belt past a line of sorters making the selections, and the belt often vibrates to shake out bad grapes hiding under good ones. Once the best grapes have been selected, they go on to be crushed. Manual sorting may be carried out before or after destemming, while automated sorters are only employed after destemming. An optical sorter has a pre-draining screen, after which the material is spread and imaged; the images are processed and defects are removed by valved air jets across the width of the sorter. In some low-throughput devices (under 5 tonnes per hour) the material is imaged and defects removed while it falls by gravity, while in higher-throughput equipment (around 10 tonnes per hour) the material is spaced out and imaged on a high-speed conveyor belt and defects are removed as the material is projected off the belt.

• Optical sorter software can use parameters such as shape in addition to colour to distinguish objects; one model, the Raytec Vision Dionysos, also detects vegetal matter in the near-infrared based on chlorophyll excitation and fluorescence
• When a defect is identified, a specific valve opens and shoots a jet of air to reject it into a waste bin; the CITF Alien sorter instead uses delta robots to move a hose to the defect and vacuum it away
• The Dionysos allows three-way sorting, with defects removed into two bins, so over-ripe grapes could be kept separate from MOG and still be made into wine
• Density bath sorters work on a different principle: whole berries roll into a sugar or juice bath of set density, where ripe grapes sink and unripe grapes and other debris float

Whether sorting is worthwhile depends on many factors, such as wine style, price point and grape condition, and whether white or red wine is being made is likely to make a big difference to the effect of residual vegetal matter. For white wine, only very high levels of vegetal matter might be expected to affect quality, since juice and vegetal matter are typically in contact only very briefly before pressing. For red wine, residual vegetal matter is more likely to affect quality because it stays in contact with the juice and wine during fermentation. Earlier research has found that 1% residual vegetal matter can have a negative impact on quality for some red wines.

• In a study of Shiraz, leaves alone did not contribute to green flavour, while stems were a bigger contributor to green aroma character and increased methoxypyrazine concentrations
• Wines made with added stems in that study were also rated higher in astringency, colour intensity and acidity
• Damaged fruit is likely to carry much higher populations of microorganisms such as acetic acid bacteria and oxidative yeast, and sorting fruit prior to processing is one tactic for dealing with damaged fruit
• In one set of trials of sorting equipment, vegetal matter before sorting ranged from 0.4 to 1.7% and residual vegetal matter after sorting from 0.1 to 0.4%, with grape losses of 0.2 to 4%

Most mass-produced wines are now harvested mechanically, which is less expensive and faster but increases the need to sort the grapes. In Australia, a 2016 survey found that smaller wineries were more likely to perform some sorting than larger ones, and hand sorting of bunches was the most common technique. The small number of automated sorters in Australia may reflect the limited amount of manual sorting there relative to some other regions of the world, which makes capital investment in automated equipment difficult to justify because there are no labour savings to offset it.

• Among Australian wineries crushing more than 10,000 tonnes, use of roller sorting had risen since 2016 from 4% to at least 16% by March 2019, typically only for more premium grapes
• The benefits of sorting white grapes are also open to debate, since any solid contaminants in the load are removed during draining and pressing shortly after arrival at the winery
• Destemming and sorting can also happen on the harvester; in 2016, 6% of red and 5% of Australian machine-harvested white grapes (by hectare) were destemmed on-harvester

The first published optical sorting trials on winegrapes came from Falconer and Hart in 2005, and equipment has been available from wine industry suppliers since around 2008; by 2019 numerous suppliers sold optical sorters to the wine industry, including Bucher-Vaslin and Pellenc. In Bordeaux, Château Pavie began working with a new sorting table that removes the stalks far more gently than previous generations of machines and then passes the grapes through an optic camera to eliminate those without pre-determined quality factors such as sufficient must weight. This new breed of sorting machines started at around €100,000. At Château Léoville Barton, the harvest was dropped onto a single sorting table before machine de-stemming.

• In 2016, optical sorting was in use at only 1.5% of Australian wineries crushing more than 50 tonnes, against roller sorting at around 6%
• Château Pavie owner Gérard Perse predicted: "In five years, the idea of manual sorting will be unthinkable"
• At Château Angélus, 50 gloved workers de-stemmed the bunches grape by grape, and owner Hubert de Boüard held that the almost entirely unscathed grapes made sorting tables almost redundant
• The Raytec Vision Dionysos costs around $250,000 and Raytec rates it at around 8 t/hr; at the 2018 edition of Vinitech-Sifel in Bordeaux, CITF put the defect removal speed of its Alien sorter at 400 defects per minute

Manual sorting is slow and highly labour intensive, and requires great concentration. On the equipment side, density bath and optical sorting systems are significantly more expensive, about 5 to 10 times, than the more basic mechanical sorting systems, but offer more sophistication when trying to remove very unripe or diseased grapes and contaminants rather than just vegetal matter. The performance of sorting after destemming will always depend on the condition of the grapes and the gentleness of the destemming process, and is likely to be reduced if the grapes have been broken down too much.

• The settings that determine which material an optical sorter removes can easily be modified using software
• A basic density bath sorter, the SOCMA Densibaie, costs around $40,000 with a nominal maximum flow rate of 4 t/hr
• Roller sorters allow reasonably high throughputs, in the order of 10 t/hr, for their price, and newer Pera-Pellenc and Bucher-Vaslin systems reach the order of 50 t/hr
• As with most sorting systems, there are likely to be other required peripherals and associated costs

Primary sources: https://www.awri.com.au/wp-content/uploads/2019/01/Nordestgaard2015-DestemmingSortingPart1and2.pdf, https://www.awri.com.au/wp-content/uploads/2019/04/Nordestgaard2019-GrapeSorting.pdf, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-matter-other-than-grapes-mog/, https://extension.oregonstate.edu/crop-production/wine-grapes/dealing-damaged-fruit-winery. Secondary sources: https://www.winespectator.com/articles/wine-harvest-101-basics-of-crush, https://www.decanter.com/wine-news/lasers-to-overtake-manual-sorting-in-hi-tech-bordeaux-64473/, https://www.winespectator.com/articles/how-is-wine-made-basic-winemaking-steps-explainer. Last verified 2026-10-04