Reeling: 2nd Attempt

Yesterday I tried reeling again. This time I used water at around blood temperature (37 degrees C) as measured with my sugar thermometer.

I had suspected that one of the reasons the cocoons are boiled is to kill the pupae, and the only reason the pupae are killed is to stop them from destroying the cocoons with enzymes from their saliva (as they hatch from the cocoons into a moths). I wondered if it would be possible to not kill the pupa and still reel some silk by keeping the water warm rather than hot, removing not all of the cocoon and allowing the pelade (inner section) to stay intact.


This did not work too well. After brushing the cocoons with a toothbrush in the water, which removed all the outside floss, I succeeded in getting a long thread but it was so fine that it kept breaking. In this video you might just be able to make out the thread as it is reeled from the cocoon...



So I then handed over to Hodmandod Senior who has far more patience, and he succeeding in brushing five of the cocoons and finding the ends of each of them. He then attempted to pull them from the cocoon together as they do in 'filatures' (factories that reel silk from cocoons), but the silk kept breaking after about a couple of metres (I'd thought that maybe if they were reeled and twisted together they might not break so easily).

So I am wondering now that it is actually necessary to heat the water to boiling to dissolve the siricin glue and hence loosen the fibres (or bave) so that they can be reeled from the cocoon.

However, I don't think I am going to find out. Since the water was getting a little cold I warmed it a little and, as the cocoons were bobbing around in the water, I am sure some of them rolled on their own - perhaps the pupa were reacting to the warmth - so we took them out and dried them. They are in the airing cupboard again now, and now when I look at them this morning they look unnaturally clean and perfect - as if they were made by machine rather than the erratic moving of the head of an insect.


Added later. A paper in the Journal of Insect Biotechnology and Sericology in 2005 described a new race of silkworms that spun cocoons composed of 98.5% sericin. According to this article sericin dissolves only after being either hydrolysed by alkaline detergent or autoclaved at 115 degrees C for ten minutes. Each of these, I suspect, would kill the pupa inside the cocoon, so it looks unlikely that it is possible to successfully reel silk from a cocoon without destroying the pupa inside.

Reeling: 1st attempt

My first attempt at reeling was not a great success. However, I am going to report what I did anyway.

I boiled a little water in a pan, and then turned off the heat. After allowing it to cool for a few seconds I added the semi-opaque cocoon. It floated.


I then stirred the cocoon in the water for a few minutes until it leaked, filled with water and sank. I then noticed that some of the cocoon had come away from the rest. I have discovered that this is because a silkworm silk consists of two proteins - two strands of fibroin which are insoluble (the brin), and sericin which glues the two brin strands together. The sericin glue is water-soluble, and some of this dissolved enough for me to catch some of these fibroin strands on my pencil.


Unfortunately, I couldn't get a single thread of silk (a bave = two brin glued together), and resigned myself to pulling away several fibres at once. However, I kept pulling, and found that more and more silk came away from the cocoon until there was only some residual silk left surrounding the pupa. This silk (called the pelade) is slightly different from the rest of the silk in the cocoon and is generally left behind in the reeling process. In cross-section, under the microscope, the silk fibres of the palade look flat, whereas silk fibres of the main part of the cocoon have a circular cross-section. The silk of the outer floss is different again, and is elliptical.



So the silk I eventually wound around my pencil wasn't a single fibre. It was also of variable thickness and fairly short. I am blaming this on the inferior quality of the cocoon and the lazy nature of the silkworm inside, which obviously couldn't be bothered to finish the thing off.

I know this because after I had finished I looked at the 'corpse' inside the cocoon and discovered that it looked like the beginnings of a pupa.


Even though I found this slightly disturbing I have to confess that a small part of me also wondered how it would taste like fried in oil.