Synchronising Cherry Ripening:
One of the major factors which determines the success of a machine-harvested coffee plantation is the proportion of the total crop that can be harvested as prime ripe coffee, ideally in a single pass. Uneven cherry ripening at harvest results in yield losses, processing difficulties and reduced quality. Concentrated ripening is not as important for hand-harvesting where only ripe cherry is picked and the unripe cherry left to pick later, although it does concentrate labour requirements.
The factors which affect the ripening pattern at harvest are;
• The degree of flower synchronisation and the time of peak flowering.
• Cherry life the time it takes the cherry to change from ripe to overmature (see maturity classification of coffee cherry table below).
• The position of cherry on the tree.
• Orientation of trees to the sun.
The pattern and timing of flowering directly influence the pattern and timing of cherry ripening. Flowering can be manipulated to favour synchronised cherry ripening with irrigation scheduling. Irrigation scheduling helps control flowering because of the coffee tree’s unusual flowering mechanism. After the flower buds form they become dormant and only blossom 10 days after rainfall following a period of drought. Research has found that this mechanism can be harnessed with irrigation scheduling. The trees are first water-stressed and then irrigated heavily to trigger flowering.
If water-stressing and rewatering are carried out at the correct time and for the correct duration (see article ‘Procedure for Synchronising Coffee Cherry Ripening’) synchronised flowering can be achieved (see Coffee Leaf Sampling article: Table of Optimum Leaf nutrient levels).
Under some conditions, this may allow single pass machine-harvesting. In some climates cherry maturity may extend over several months unless synchronised flowering is attempted. Extended ripening will reduce recovery of prime cherry because overmature and immature cherry are harvested during the several harvester passes required.
The timing of flowering is also manipulated by the timing of waterstressing and rewatering. This in turn influences the time of year (hence climate) during which cherry ripens. The climate during ripening is the major factor influencing cherry life. In North Queensland, water-stressing is delayed until mid-October so that flowering can be delayed until November/December. Ripening then occurs in the cool dry months of June to August when cherry life is greatest.
Cherry life is controlled by both climatic and plant factors. If cherry ripens under cool (mean daily temperature below 18°C) dry conditions, it remains on the tree in the prime ripe state (see cherry muturity classification table above) for several months. This can even allow time for cherry developing from different flowerings to ripen together, so even if flowering is not synchronised a large proportion of the total crop can be harvested at one time. This tends to occur in northern New South Wales. In North Queensland, where the climate during ripening is warmer and wetter, especially if peak flowering occurs before September-October, cherry can change from ripe to overmature within a few weeks. In these conditions, it is important to synchronise and delay flowering so that cherry ripens in the coolest, driest months of the year. This will maximise the proportion of prime ripe cherry that can be harvested at one time. These findings indicate that the importance of synchronising flowering to synchronise cherry ripening depends on the climate during ripening.
Another factor influencing cherry life is tree health and foliage cover. In healthy, heavily foliated trees, cherry life can be four to six weeks greater than in trees in poor health. Shading from leaves accounts for the longer cherry life (four to six weeks) in the bottom part of the tree compared with the upper branches.
The final factor influencing cherry life is the apparent acceleration of the maturing process following a harvester pass. This phenomenon has also been observed in other berry crops and is useful where more than one harvester pass is carried out (see coffee harvesting articles).
Position of cherry:
Even when synchronised flowering has been achieved, cherry tends to ripen from the top of the tree down. This is especially true in tall cultivars and in older trees. In young trees less than four years old and dwarf cultivars, a top to bottom ripening pattern is less distinct. This ripening pattern occurs due to different micro-environmental conditions within the tree. In North Queensland, cherry in the bottom part of the tree typically ripens four to six weeks later than in the top part of the tree. This gradation in maturity has led to the practice of layer harvesting (see articles on coffee harvesting) which can greatly improve the recovery of prime ripe cherry.
The alignment of tree rows (east-west, north-south) can have a significant effect on cherry ripening on different sides of the tree and presents problems for machine-harvesting. In New South Wales north-south rows minimise the ripening difference between tree sides, whereas an east-west orientation reduces maturity variability in North Queensland. An east-west orientation also protects trees from the damaging effects of direct afternoon sun in extreme temperatures.
Irrigation and stressing trials have helped develop the best strategy to synchronise flowering. This strategy requires a reliable dry period of two months between September and December and an efficient irrigation system (preferably drip) over which you have precise control. It is an advantage if the irrigation system can be controlled separately in different parts of the plantation to allow for differences in irrigation requirements between cultivars, tree ages and soil types. See also Informed Farmer’s article on ‘Procedure for Synchronising Coffee Flowering.’
Source: James Drinnan