FRENCH BEANS POST HARVEST

1.0 Introduction

This training module will be used for training Field Staff (TOT), who will then train the farmers. The training at both levels will be interactive and will use live specimens for demonstration. The training will therefore be based near a farm or at least the trainees will be able to visit a farm of the produce at the period when harvesting and post-harvest handling are being carried out for practical demonstration.

French beans are pod vegetables which contain immature seeds. After detachment from the mother plants, the pods are highly perishable due to their large surface area to volume ratio. Post-harvest management of the fresh vegetables such as precooling and packaging are very important in maintaining quality. Other post-harvest handling processes for marketable produce include sorting and grading.

Both quantitative and qualitative losses occur in horticultural commodities between harvest and consumption. Qualitative losses, such as those in edibility, nutritional quality, caloric value, and consumer acceptability of fresh produce, are much more difficult to assess than are quantitative losses. Quality standards, consumer preferences and purchasing power vary greatly across countries and cultures and these differences influence marketability and the magnitude of post-harvest losses. This module therefore intends to help the horticulture smallholder farmers gain knowledge and practice:

1. Identification of the maturity indices of French beans.
2. Appropriate methods of harvesting French beans.
3. Sorting and grading French beans.
4. Appropriate packaging for French beans for the market.
5. Appropriate methods of storing French beans.

2.0 Pre-Harvest considerations

French bean or green bean (Phaseolus vulgaris L.) pods are vegetables consumed fresh or processed. It is considered a highly perishable vegetable because it is harvested immature and has a high moisture content. Storage life of green bean pods does not exceed 21 days under favorable refrigerated storage. The visual quality of pods is one of the most important quality parameters affected due to rapid deterioration after harvest. Many nutritional and compositional changes occur after harvest and during storage.

Harvesting starts at 6 to 8 weeks after planting depending on the variety and ecological conditions.  It is best done in the morning but not when the crop is too wet and is achieved through carefully picking the pods off the plant with the stalks, and not pulling. This should be done at regular intervals depending on the market specifications, for instance, twice a week for the fine French beans and three times a week for the extra fine beans, and can continue for around a month. Harvesting the beans while young encourages more production, and the beans are tastier.

3.0 Harvesting

Begin picking the pods when they are 10cm (4in) long. Pods are ready when they snap easily and before the beans can be seen through the pod.  Picking of pods begins six to eight weeks after planting, depending on the area and variety, and continues for about one to two months. The pods are carefully picked, and not pulled from the plants, and should have the stem attached to them. Harvesting may be done twice a week for the fine beans and three times a week for the extra fine beans. This continues for around three weeks. One gets a yield of 9 to 15 tonnes/ha and 6 tonnes/acre in 2 and 1/2 months.

Hand harvest should be done gently to avoid damage to the pods and plants. Over handling and rough handling of pods should be avoided to reduce visible and latent damage. All mature pods should be harvested, and immature pods should be allowed to remain for the next harvest. It is recommended to harvest all mature pods before moving to the next plant. Bean pods should be moved immediately to shade in the field until transfer to further processing. Green bean pods should not be exposed to direct sunlight to reduce pod temperature which reduces quality.

4.0 Post harvest handling

4.1 Precooling

After harvest, French bean pods should be immediately cooled to eliminate field heat, reduce respiration, microbial growth, and shriveling. The best precooling method is forced air cooling. This method could accelerate water loss due to cold air movement around pods, so the cooling process should be monitored and managed to remove the crates of beans as soon as they reach the 7/8th cooling temperature. For example, if the desired temperature is 7 °C, and the initial temperature is 27 °C, the 7/8th cooling temperature is 10 °C. To avoid the expense of precooling, the beans can be harvested very early in the morning, around 4 – 5 am to take advantage of the low morning temperatures and maintain the cool in the produce, then immediately place them under the shade or deliver them to the processing plant.

4.2 Sorting and grading

Elimination of unacceptable pods (immature, over matured, broken, and diseased) is necessary after harvest, to reduce the spread of postharvest diseases and enhance the quality grade. Gentle handling is essential to prevent damage. Sorting is done in order to get rid of broken, twisted and perforated pods as well as plant debris while grading should be done according to size of the produce. The French beans for the market are graded as follows after sorting:

Extra fine pods: very tender, turgid, seedless and without strings. The pods should be less than 6mm width and minimum length of 10cm.

Fine pods: have small seeds, soft strings, turgid and tender. Pods width of 6-9mm and length of 12-14cm.

Bobby beans: beans of marketable quality but not inclusion in the high class. Must be of reasonable tender and seed should not be too large.

4.3 Packaging

Packing affects French bean pod quality. Weight loss and decay of pods are reduced by the selection of suitable packaging (Trail et al., 1992). French beans are packed in several types of containers, depending on the demands of the market and consumer. The most common containers are fiberboard boxes and perforated polyethylene bags. Use of food grade polyethylene bags for French bean pods will help to reduce water loss, conserve total sugars, reduce chlorophyll degradation and vitamin C loss. Polyethylene bags for packaging highly perishable crops work best under refrigerated conditions during shipping and storage.

French beans can also be packed in perforated corrugated fiberboard cartons of different sizes or in plastic crates. Pre-cool the pods and store in a cool at 7-8C and R.H of 95%-100% for 1-2 weeks.  Soon after packing, the produce should be kept in a cool place to await loading into the store. At 4oC, and a relative humidity of about 80%, French beans can store for a week. For the retail market, the beans can be placed in sealed and perforated plastic packages (seal packaging). The beans can be packaged in this manner after snipping although the shelf-life in the store will be much shorter than for the un-snipped.

4.4  Transport

The type of transport is important and can affect the quality of green bean pods due to their high-water content and short shelf-life. Transport from the field to packinghouse is the first step which takes place usually by manual hauling. This process should be done as soon as possible after harvest to reduce water loss and respiration rate. The quality of refrigerated transport, distance between the farm and the market, and road quality are factors which determine the level of loss occurring during transport.

5.0 Causes of Post-Harvest Loss in French Beans

Water loss leading to shriveling and weight loss.

Microbial growth leading to rotting and decay.

Chilling injury if stored in refrigerator.

Physical injury due to poor handling.

6.0 Post-Harvest diseases & Pests

I.Gray Mold

 Gray or white mold on beans is an indicator of either a fungus or bacterial infection.  Powdery or downy mildew (usually found only on lima beans) is caused by fungal spores that germinate on dry foliage when the humidity is high. Especially common in the late summer and fall, these mildew diseases do not usually kill the plants, but it does stress them, potentially resulting in  less crop yield. To mitigate the possibility of either powdery or downy mildew, avoid water stress, prune out any infected leaves and pods, and keep the garden free of plant detritus. Also, be sure to rotate the bean crop each year.

II.Anthracnose

Caused by Colletotrichum lindemuthianum and can be destructive in hot humidclimates. The underside of leaves become reddish and angular spots appear on the upper surface.  The pods have typically round, dark brown sunken spots with orange coloured borders. Each spot is about 5mm in diameter.  The spots are the hub of millions of spores that are released under humid conditions.  The red brown spots are also found on the stems. The fungus overwinters on rotten material around fields. To control it, plant certified seed or seed from reputable companies, Plant at the recommended planting dates and spray every 7-14 days depending on disease pressure. When first signs of symptoms appear don’t hesitate to spray as it might be too late and yield losses can be incurred.

7.0 Evaluation of Training

This evaluation can be done as a quick written test during training of field staff. For farmer training, it can be done as a guided discussion of the answers to the questions by the trainer, in a plenary session. It is meant to assess the extent of learning.

1. Describe the maturity of French beans at harvesting.
2. Describe the most appropriate method of harvesting French beans.
3. Explain the sorting and grading of French beans.
4. Describe the cleaning and disinfection of French beans and give reasons for the operation.
5. Describe the drying process of French beans and give reasons for the same.
6. Enumerate the spoilage factors of French beans and their control.
7. How may chili be packaged for storage and for marketing.
8. Give the storage conditions for French beans chilies.