This page, which regularly changes, provides discussion of various aspects of quality in wine: how producers achieve high quality, and how it can be recognized in the glass. The current topic is harvesting and sorting of grapes. My Blog will have articles with a more 'chatty' approach.
The timing and method of harvesting have a major impact on quality. A grower or producer's decision as to when to harvest will be decided upon with respect to many factors, including seasonal parameters, the weather forecast, the risk of botrytis, the balance of sugar and acidity in the grapes, the maturity of skin and seed tannins and the formation of aromas and aroma precursors. Of course, as the harvest cannot be organised at a moment's notice, careful analysis and sophisticated prediction tools are employed.
Historically, especially in some regions of the Old World, many growers would pick early - in fact pick too early for the grapes often lacked phenolic ripeness or even the desired levels of sugars. Growers also lived in fear of autumn rains spoiling the harvest with bunch rot and dilution and so undertook early 'insurance' picking. In order to ensure that the grapes have an acceptable, minimum level of ripeness, the rules of Appellation d'Origine Protégée (Appellation Controlée) include, in most regions, a 'ban de vendage', a date variable each year before which the harvest may not take place. Nowadays, growers more often wait for phenolic ripeness which, in warm and hot climates this may not come until after the desired levels of sugar and acidity are present. This can result in over-alcoholic and over-loud wines. However, due to climate change and alterations in canopy management, harvesting in now taking place earlier in the season
Some viticulturalists claim that in order to pick the right fruit at the right time machine harvesting is essential. A machine can pick in 1 day the quantity of grapes that would require 40-80 manual pickers. The technology of mechanical harvesters has improved considerably during the last 25 years. The harvesting system generally now used is that of bow-rod shakers. The fibreglass rods move the fruiting zone of the vines to the right, and then rapidly to the left, and using the principle of acceleration and sudden deceleration of a mass the grapes are easily snapped off the stalks, which are left as skeletons on the vines. Lightweight berries, including shot berries, raisins and those that have been bird eaten do not have the mass, and so are left behind. The fruit is initially collected on conveyers comprising interconnected shallow baskets which are moving in a rearwards direction at the same speed as the harvester is moving forwards. MOGS (matters/materials other than grapes) are removed by two methods: spinning blades just above the trays will remove large MOGS, and vacuum systems remove light matters such as leaves. Some of the latest design mechanical harvesters are now able to pick whole bunches.
Advocates of mechanical harvesting cite the several advantages:
- Machines work fast and the grower can utilise them at the time of optimum grape ripeness.
- The fruit picked is cleaner than may be the case with unskilled and/or piecework labour.
- Machines pick at a controlled rate so there should be no delay in processing, which gives an advantage over manual picking which can result in queuing for the sorting tables and destemmer/crusher which would result in fruit deterioration.
- Machines can work at night and deliver desirable cool fruit to the winery.
- Cost of picking is generally less than half that of using manual labour although the cost of the machine has to be amortised.
However, machines may damage fruit, particularly where the berry is attached to the pedicel, and unwanted oxidation may begin immediately.
In spite of considerable improvements during recent years, machines do damage grapes to a small extent. Trained pickers can select fruit according to requirements and pick into small bins, sometimes just 12 kg capacity, which will also minimise fruit damage. Hand picking is the only option if the winemaker wishes to vinify separately the product of small parcels of individual terroirs. Hand picking is essential if whole clusters are needed for white wines, and there is a growing trend for red wine makers to use at least some whole clusters in their ferments.
Delivery of fruit to the winery
Ideally, the fruit should be transported to the winery in small containers, so it does not crush itself under its own weight. Grapes should be processed as soon as they are harvested - some top producers aim to have fruit in the crusher within 1 hour of picking. The longer the grapes are left waiting before they are processed, the more risk there is of bacterial spoilage or oxidation. This is particularly important in a hot climate, when the process of deterioration is much faster than in cool regions. Flies of the species Drosophila suzukii and Drosophila melanogaster, are immediately attracted to damaged fruit, and their digestive tracts contain acetic acid bacteria. Should there be any delay in processing, protecting the bins of fruit with dry ice will help prevent deterioration.
Selection and sorting
The purpose of sorting is to remove unripe fruit and altered fruit, that is fruit affected by rot. Sorting can take place at a number of points:
(1) Rogueing the grapes whist on the vine - particularly useful if they are to be mechanically harvested.
(2) Selection by the pickers, who may be instructed which fruit to harvest and which to leave on the vines.
(3) Sorting at a table on a trailer situated at the ends of the rows of vines, the fruit being sorted manually by people on each side of a moving belt.
(4) Upon arrival at the winery clusters or, in the case of machine harvesting, berries, sorted manually by people on each side of a moving belt or vibrating table
(5) After de-stemming (in the case of hand-picked grapes), or the berries of machine harvested grapes.
There are now several designs of mechanical sorters, including those that identify the differing masses of healthy and damaged grapes, and these can be particularly valuable where the cost or skills of labour are a major issue. Optical sorting machines are increasingly used, but their high cost may prohibit their availability to the small estate. A machine that works by separating grapes by grape density, the 'Tribaie', has proved very successful particularly with mid-sized producers. Vibrating and moving belt tables remain a popular and efficient alternative, but are by definition, labour intensive.