ICS 67.120.99  
 
Reference number
DRS 357 -3: 2020
© RSB 2020
  
 RWANDA 
STANDARD  DRS
357-3
First edition
2020 -mm-dd
Silk cocoon production — Code of practice 
— Part 3: Silk cocoons handling  
   
DRS 357-3: 2020  
©RSB2020 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB2020  
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ePortal: www.portal.rsb.gov.rw  DRS 357-3: 2020  
iii                ©RSB2020 - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................... iv 
1 Scope  ................................ ................................ ................................ ................................ ................ 1 
2 Normative references  ................................ ................................ ................................ ....................... 1 
3 Silk cocoon handling ................................ ................................ ................................ ........................ 2 
3.1 De-flossing of fresh cocoons  ................................ ................................ ................................ ........... 2 
3.2 Packaging of fresh cocoon  ................................ ................................ ................................ .............. 2 
3.3 Transport of fresh cocoons  ................................ ................................ ................................ ............. 3 
3.4 Sorting  ................................ ................................ ................................ ................................ .............. 3 
3.4.1  Sorting frequency  ................................ ................................ ................................ ............................. 3 
3.4.2  Sorting procedure  ................................ ................................ ................................ ............................ 4 
3.5 Cocoons grading  ................................ ................................ ................................ .............................. 4 
3.6 Cocoons drying and storage  ................................ ................................ ................................ ........... 4 
3.6.1  Drying conditions  ................................ ................................ ................................ ............................. 4 
3.6.2  Dried cocoon storage  ................................ ................................ ................................ ....................... 5 
4 Record keeping  ................................ ................................ ................................ ................................ 7 
 DRS 357-3: 2020  
©RSB2020 - All rights reserved                  iv 
 Foreword  
Rwanda Standard sareprepared by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task o f technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 357 -3 was prepared by Technical Committee RSB/TC 029, Textile and Leather Technology . 
In the preparation of this standard, reference was made to the following standard  (s): 
1) TAS 8201 -2012 Good practices for silk cocoon production  
2) Sericulture training manual for farmers in Rwanda  
The assistance de rived from the above source is hereby acknowledged with thanks.  
DRS 357 -3 consists of the following parts, under the general title Introdu ctory element — Main element : 
 Part 1: Mulberry leaves production  
 Part 2: Mulberry silkworm rearing  
Part 3: Silk cocoons handling  
Committee membership  
The following organizations were represented on the Technical Committee on Textile and Leather 
Technology (RSB/TC 029) in the preparation of this standard.  
Ministry of Trade and Industry (MINICOM)  
University of Rwanda -College of Science and Technology (UR -CST)  
National Agricultural Export Development Board (NAEB)  
 Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA)  
HeWorks Silk Rwanda Ltd  
Rene Pharmacy  DRS 357-3: 2020  
v                ©RSB2020 - All rights reserved  
 UTEXRWA Ltd  
OXALIS Ltd  
LIXIL/SATO  
Rwanda Standards Board (RSB) – Secretariat  DRS 357-3: 2020  
©RSB2020 - All rights reserved                  vi 
 Introduction  
Sericulture is an agro -based sector, involving rearing silkworms to produce silkworm cocoons and raw silk by 
reeling cocoons. The major sericulture activities comprise of mulberry cultivat ion to feed the silkworm larvae, 
silkworm rearing to produce cocoons, reeling of cocoons to unwind the silk filament and silk process ing and 
weaving to gain value added silk products.  
The growth and development of silkworm is greatly influenced by environm ental conditions. The biological as 
well as cocoon -related characters are influenced by ambient temperature, rearing seasons, quality mulberry 
leaf, and genetic constitution of silkworm strains. Different seasons affect the performance of Bombyx mori L . 
Silkworm rearing depends on the availability of mulberry leaves. It is occasionally limited by the dry  season, 
which is the time to avoid silkworm rearing because mulberry growing isretarded due to drought and 
exceeding high temperature gives rise to the ret ardation of silkworm growing.  
 DRS 357-3: 2020  
1                ©RSB2020 - All rights reserved  
 Silk cocoon production — Code of practice — Part 3: Silk cocoons 
handling  
1 Scope  
This Draft Rwanda Standard provides guidance on good practices for post -harvest cocoon handling activities 
namely de -flossing, packaging of fresh cocoons, means of transportation of fresh cocoons to the collection 
centres , sorting, drying and storage . 
2 Normative references  
There are no normative references in thisdocument . 
3 Terms and definitions  
For the purposes of this standard, the follow ing terms and definitions apply . 
3.1 
cocoon  
outer protective shell spun by silkworm larva covering itself before t ransforming into pupa stage  
3.2 
fresh cocoon  
cocoon that consists of a live pupa and shell with or without de -flossing  
3.3 
dried cocoon  
cocoon that consists of a dead pupa after getting dried   
3.4 
defect cocoon or poor cocoon  
cocoon whose shape is with abnormal characteristics i.e. double cocoon, pierced cocoon, inside soiled 
cocoon, outside soiled, thin -shelled cocoon, loose -shelled cocoon, thin -ended cocoon, malformed cocoon, 
printed cocoon, crushed cocoon, and mouldy cocoon   
©RSB2020 - All rights reserved                  2 3.5 
floss  
short or waste s ilk fibers, especially from the outer surface of the cocoon of a silkworm  
3.6 
stifling  
process in which, the pupa inside the cocoons are killed by subjecting them to high temperature trea tment via 
sun drying, steam or hot air in order to maintain the cont inuity of silk filament making up the cocoon  
4 Silk cocoon handling  
The proper handling of s ilk cocoons results in good quality silk products.  The following are activities to be 
controlled for better results:  
4.1 De-flossing  of fresh cocoons  
After harvesting, all loose fibres on cocoons surface are removed, giving it a clean look. If flosses remain on 
the cocoon, they stick to one another and it becomes difficult to sort the cocoons. Failure to de -floss cocoons 
also lowers the marketability of the cocoon. The f loss should be remove d by hand or using a de -flossing 
machine if available.  
 
Figure 1 Harvested cocoons with floss        De -flossed cocoons  
4.2 Packaging of fresh cocoon  
After harvesting, de -flossing  and sorting , cocoon s are packed in clean baskets or a woven polypropylene 
bags. The recommended quantity of cocoons to be packed is as per Table 1.  
Table 1 —Quantity of cocoons to be packed  
S/No Type of packaging material  Nominal capacity 
/size Acceptable quantity of 
cocoon (kg)  
i.  Baskets  - 15 
DRS 357-3: 2020  
3                ©RSB2020 - All rights reserved  
 ii.  Woven po lypropylene (Kg)  50 15-18 
iii.  100  33 
 
4.3 Transport of fresh cocoons  
After proper harvesting and removal of diseased or damaged cocoons, the fresh cocoons are  taken to the  
Cocoon collection center (CCC) . For short distances, the farmer may carry the cocoons in baskets or bags. lf 
the distance is longer,  cocoons should be transported using any suitable means with precautions  to avoid 
damage, vibration and shock. The following precautions should be considered:  
a)  It is advisable to avoid carrying cocoons over lo ng distances, however, in case of transportation, use of 
P.V.C. containers with 15 kgs capacity is recommended.  
b) Shock absorbers  to prevent damage over long distances should be used  (i.e. Sponge, saw dust, husk, .).  
c) For the purpose of good hygienic practice s, cocoon should be pack  
d)  Fresh cocoons should arrive at the CCC within tw o to three days after harvest.  
 
4.4 Sorting   
4.4.1  Sorting frequency  
3.4.1 .1 When reeling is carried out with irregular and non -uniform cocoons it results in thread breakage, poor 
reelability,  decreased raw silk recovery, variation in raw silk denier, and poor neatness.  
3.4.1.2  The types of defects encountered in the sorting process are: inside soiled cocoons, outside soiled 
cocoons, cocoons with prints of cocooning frames, flimsy or loose -shelled cocoons, perforated cocoons,  thin -
end cocoons, thin -shelled cocoons, fluffy cocoons and mouldy cocoons.  
3.4.1.3  The recommended number of times the sorting should be carried out is as follows:   
a) Silkworm farmers remove defective cocoons as well as do uble cocoons before taking the produce to the 
Cocoon collection center.  
b) At the reception of cocoon collection center, cocoons sorting shall be done for the second time, to ensure 
good quality cocoons for reeling,   for accurate verification.   
c) Before processing, dried cocoon shall be sorted   
©RSB2020 - All rights reserved                  4 
 4.4.2  Sorting procedure  
Cocoons are spread out on a table and the sorter pick out the defective cocoons by visual inspection  and 
place them in separate containers. The sorting room is generally located close to the cocoon  stores and 
should be provided with good ventilation and lighting.  
4.5 Cocoons grading  
After sorting, cocoons fall into the following grades:  
3.5.1  Grade I: Good quality cocoons,  which do not have defects  
Note:  under Grade I, the quality of cocoon may vary i n accordance with the cocoon unit weight and shell ratio.  
3.5.2  Grade II: Defective cocoons, including inside soiled cocoons, outside soiled cocoons, cocoons with 
imprints of cocooning frames, malformed cocoons,  
3.5.3  Grade III: Double cocoons , made by two  silkworms cooperatively.  
3.5.4  Grade IV: Waste cocoons, including : perforated cocoons, thin -end cocoons, thin -shelled cocoons, 
loose -shelled cocoons, fluffy cocoons and mouldy cocoons.  
4.6 Cocoons drying and storage  
4.6.1  Drying conditions  
3.4.1.1  The drying temperature impacts the qua lity of the cocoon and the resulting raw silk. If the 
temperature exceeds certain limits, sericin degenerates and concurrently efficiency, reelability and  raw silk 
percentage declines. It is advisable to observe the fo llowing limits: for hot air drying 11 5±50C is recommended 
on contact with the coc oon, for steam -heat drying 102 ±20C is the preferred guideline.  
3.4.1.2  While setting higher finishing temperature increases drying efficiency, the melting point of sericin  
declines when the drying rates exceeds 50 percent. The finishing temperature should be reduced graduall y 
from 600C in hot air drying and 550C in steam -heat drying.  
3.4.1.3  Cocoons that are to be stored for long periods prior to reeling need to be dried to the  optimum 
levels. The complete drying process covers band one up to eight  within provided temperature and duration  as 
per table 2  
Table 2 —Perfect drying for long term storage (Hot Air Circulating Type)  
Band No.  1 2 3 4 5 6 7 8 
Temperature( ) 110 105 100 90 85 83 62 60 
Humidity (RH%)  3-4 8-10 20-23 
Degree 
Drying(%)  100-85 85- 69 69-59 59-51 51-46 46-43 43-42 42-40 
Period(min.)  45 45 45 45 45 45 45 45 DRS 357-3: 2020  
5                ©RSB2020 - All rights reserved  
  
For short term storage,  cocoon drying is performed under conditions of temperature and relative humidity as 
per Table 3.  
Table3 — Half Drying Cocoon (Hot Air Circulating Type) for short term storage  
Band No.  1 2 3 4 5 6 7 8 
Temperature( ) 110 110 100 100 93 93 80 72 
Humidity(RH%)  3-4 5-7 15-18 
Degree 
Drying(%)  100-90 90-79 79-70 70-68 68-62 62-57 57-53 53-50 
Period(min.)  27 27 27 27 27 27 27 27 
 
8.1.5  Cocoons for reeling without storage require hot air drying of cocoons is in place  of steam stifling as 
per Table  4 
Table 4 –Drying temperature (cocoons for reeling without storage)  
Steps  Temperature  Duration  
1.  110-100°C  45-60 minutes  
2.  100-90°C  45-60 minutes  
 
4.6.2  Dried cocoon storage  
4.6.2.1  Storage room  
In building cocoon storage room, the following should be considered:  
a) Air space for ventilation should be provided at the bottom of the storage room,  at least 1m above the floor, 
to prevent moisture coming up from underground.  
b) the bag stack shall be built at least one (1) meter away from the walls of a stor e. This allows easy 
inspection and prevents moisture ingress from contact with the wall  
c) the bag stack shall not be built too high and not closer than 1.5 m to the store roof beams so that staff ca n 
work on top of stacks;  
d) The cocoon stores should preferably be built with double walls or make single walls as thicker as po ssible.  
e) Windows should be small and fixed at high level and provided with an exhaust fan to enable moisture 
accumulating in the room to be drawn out.   
©RSB2020 - All rights reserved                  6 f) The storage room should be lined with an iron sheet, the windows should be covered with a wire net o f 
about 1.5mm mesh   
g) Cloth or wo ven polypropylene bags are recommended as containers for dried cocoon storage.  
h) Shelves should be provided in three to four tiers to accommodate  cocoon bags to avoid piling of 
bags/baskets , in order to reduce the fungus development in dry cocoons during sto rage. 
i) If humidity exc eeds 70 percent, action should be taken to reduce humidity such heating.  Precautions 
should be taken   to prevent fire outbreak.  
j) The cocoon storage room shall be built in durable materials .  
k) The room shall be disinfected and protecte d to prevent  pests  
l)       The room shall be disinf ected and protected to prevent pests.   
4.6.2.2  Cocoons storage  
3.7.2.1  When long period s of storage are not necessary half  dried cocoons as per table 3 may be stored in 
thin layers in trays kept on wire mesh racks.   These racks may be placed in a well -ventilated room so that the 
cocoons are not affected by fungus due to presence of moisture.  
 
Figure 2  Cocoon storage racks  
3.7.2.2  For long periods of sto rage, cocoons should be hot air dried to the optimum level in order to remove 
the water content from the pupa.   
3.7.2.3  The cocoon storage room should be maintained at a temperature and relative humidity not exceeding 
25-30°C and 40 -55% respectively so th at fungus attack on the cocoon is prevented.  
DRS 357-3: 2020  
7                ©RSB2020 - All rights reserved  
 3.7.2.4  Cocoons waiting for transportation should be kept in a manner that they are not too densely overlaid  
causing accumulated heat and moisture that affect their quality.  
5 Record keeping  
The following informat ion should be recorded and kept:  
a) month -year of silk worm eggs  production  
b)  day-month -year of the first hatching  
c) day-month -year of silkworm mounting;  
d) daily temperature and relative humidity of silkworm rearing house;  
e) day-month -year of harvesting fresh cocoon ; 
f) day-month -year of cocoon  drying ; 
g) quantity of cocoons for each grade  
h) application of substances used to prevent and control silkworm diseases; and  
 
 
   
©RSB2020 - All rights reserved                  8 
 Annex  A 
(informative ) 
Characteristics of defective cocoons  
 
A.1  A double cocoon is a cocoon with more than one silkworm nest together.The silk yarn from this type 
of cocoon tends to break easily during a reeling process because there are more than one silk thread s 
twisted. Thus, the silk yarn reeling ability and efficiency is low. The derived silk yarn is uneven.  Double cocoon 
is caused by different reasons too many silkworms per frame, high temperature and high humidity. Dou ble 
cocoons are used for manufacture of a coarse, non -uniform yarn called "dupion".  
A.2  Pierced or perforated cocoon  are cocoon pierced out by  a maggot of Uzi fly leaving a hole on the 
cocoon causing silk yarn filament breaks. Thus, the silk yarn reeling ability and efficiency is low.  It can be used 
only for hand spinning or as raw material of machine spun silk yarn.  
A.3  Inside soiled cocoonor dead cocoon or melted cocoon  are cocoon which contains dead pupa 
inside or made by an infected silkworm but still on cocoon development stages. The pupa is dead and sticks 
to the inside shell of the cocoon causing a stain which yields low quality silk yarn  which is dull in colour. They 
do not make sound when shaken.  
A.4  Outside soiled cocoons  are cocoon derived from silkworm urine before cocooning or contamination 
by infected silkworms in the same frame. These are recognized by a rusty colour spot on the c ocoon shell 
caused by absorption of intestinal fluid/urine of the mature worm formed during mounting.  The cocoo ns 
become soggy before reeling and reelability is very poor.  
A.5   Thin shell cocoon s are cocoon not fully developed which is caused by infected  silkworm. The 
silkworms have only short time to spin the cocoon before they die. In other case, the mature silkwor ms are 
transferred too late and thus they spin cocoon on the side of rearing trays or tables, leaving littl e fibre when 
they are placed on a cocoon frame. It is not possible to reel this type of cocoons as they become too soggy.  
A.6   Loose shell cocoon  or Flimsy cocoons means a cocoon produced under an improper 
environmental condition whose shell is loosely spun in layers and has a low silk co ntent. These cocoons are 
easily overcooked and fibre from this type of cocoon tends to break easily when reeled.  
A.7   Thin-end cocoon : The cocoon is unusually thin at one or both ends, and when cooked thinner part 
becomes soggy leading to several filamen t breaks during reeling process. Thus, the silk yarn reeling ability 
and efficiency is low. The cause of this defect may be attributed to species characteristics or impr oper 
temperature and humidity during rearing and mounting.  
A.8   Malformed cocoon  means  a cocoon made from silkworms in an improper cocoon frame, or from 
weak silkworms. This prevents the silkworms from completing the cocooning process and the cocoons ar e 
distorted and irregular. When cooked with normal cocoons, they are either soggy easier or hard depending on 
the condition of each malformed cocoon.  
A.9  Cocoon with prints of cocoon frame or scaffold pressed cocoons means a cocoon made by a 
silkworm on the edge of a cocoon frame or on the lining paper. The cocoon is too flat with some thic ker parts. 
This is due to too many silkworms per a cocoon frame, leaving little space for cocooning. Sometimes it occurs 
because the cocoon frame is improper.  DRS 357-3: 2020  
9                ©RSB2020 - All rights reserved  A.10 Crushed cocoon  means a cocoon caused by poor handling during transportation. The cocoons are 
crashed to one another. The filament from these cocoons break easily especially at the crushed spots.  
A.11 Musty or mildwed cocoon  means a cocoon caused by an incomplete cocoon drying process and 
improper moisture control in a cocoon storage room. This condi tion allows fungus to grow in the cocoon shell. 
It is not advised to reel this type of cocoons as the filament gets deteriorated.  
 
Figure A.1 : good quality cocoons and defected cocoons  
 
  
 
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 DRS 357 -3: 2020  
 
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