Flimsy Cocoons

Here, the shell is loosely spun in layers and has a low silk content. These cocoons are easily overcooked and produce waste

Malformed Cocoons

These are abnormally shaped cocoons, which may arise from species variation. This defect may be due to racial characteristics and breeding with mulberry leaves stained with agrochemicals.

Printed Cocoons

This defect may happen due to improper mounting frames; these are also called scaffold pressed cocoons.

Outside Stained Cocoons

These are recognized by a rusty colour spot on the cocoon shell caused by absorption of intestinal fluid/urine of the mature worm formed during mounting. Reelability is very poor in this case.

Inside Stained Cocoons | Dead Cocoon

Dead cocoons are also known as melted cocoons. In this case, the pupa is dead and sticks to the inside shell of the cocoon causing a stain.

Melted cocoons are called mutes because they do not make a sound when shaken. These cocoons are difficult to process and will result in silk, which is dull in colour.

Defective Cocoons like Double Cocoon

A double cocoon is spun by two worms, producing a filament, which does not unwind smoothly and tangles easily. As these cannot be reeled along with normal cocoons, double cocoons are used for manufacture of a coarse, non-uniform, stubby yarn called "doupion".

Double cocoons may be caused by crowded mounting conditions, high temperatures, high humidity and mutation of silk species.

Different Types of Cocoons

When Cocoons are sold at the market, price is assessed on the basis of cocoon quality. This is judged by grading shell percent, filament length, reelability and the percentage of defective cocoons. If the percentage of defective cocoons is high, the price will be affected.

Transport of Fresh Cocoons

After proper harvesting and removal of diseased or damaged cocoons, the fresh cocoons are taken to the market. For short distances, the farmer carries the cocoons in bamboo baskets or jut bags on his head or by bicycle. If the distance is longer, cocoons are transported in a van or a bus. Caution should be exercised when loading fresh cocoons on to the van to ensure that containers are loosely packed in tiers to avoid damage. Vibration and shock during long trips can spoil fresh cocoons. Cocoon quality is affected by steam produced while being transferred in a bag or basket. If there are defective cocoons fresh cocoon quality will be harmed.

 

While it is advisable to avoid carrying cocoons over long distances, there are steps, which preserve silk reelability. First use of P.V.C. containers with 15 kgs capacity is recommended. Shock absorbers, such as sponge can prevent damage over long distances. To minimize the risk of heat deterioration, shipping should take place only during the night or early morning. Ideally, the fresh cocoons should arrive at the stifling unit within two to three days after harvest.

Factors Influencing Cocoon Quality

This section presents the measures to be taken during silkworm rearing and mounting to obtain a better quality of cocoons with higher silk content, longer filament, better reelability and lower percentage of defective cocoons.

Temperature and Humidity During Mounting

Maintain temperatures at or near 25ºC and relative humidity around 65 percent for silkworms to spin good quality cocoons with a high reelability.

Mounting Device

Although different mount practices are employed among producer countries, rotary mounting frames provide good ventilation. The result is improved reelability of cocoons.

Harvesting and Handling of Fresh Cocoons

Cocoons should be harvested only following complete pupation. In practice, the appropriate harvesting day would be the fifth day in tropical countries, and the seventh or eighth day in temperate countries, from the mounting date. If premature harvesting takes place, the silkworm will still be in its larval stage, weigh more, have fragile skin, and could likely be crushed, which would cause stains to the cocoon during handling and transportation.

Cocoon Quality

A Series of natural circumstances will produce variations in cocoon quality. Some of the most noteworthy include:
 

Differences in cocoon quality in the same batch

Differences in cocoons produced in the same location by different farmers who have reared the same species
Seasonal influences. In Japan for example, cocoons produced in the spring and late autumn are higher in quality than those in early autumn and summer

Environmental conditions affect cocoon reelability such as temperature and humidity
Processing technique in reeling will impact reeling efficiency as well as raw silk quality
Bivoltine cocoons are superior quality compared to multivoltine silkworm species traditional farmed in tropical zones.

Recent silkworm cultivation now develops cross-breeds of multivoltine with bivoltine silkworms as a strategy to improve overall cocoon quality.