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Low-Dough Self Sealing Inoculation Lids

A cheap method for do it yourself sealed lids

  Low-Dough Self Sealing Innoculation Technique

The purpose of this document is to desribe my methodology, in finite detail, of constructing self sealing lids at home, for pennies per lid.  The purpose of a self sealing lid is for increased sterility, as using this method cuts down on air exchange in a sterilized jar, thus preventing contaminants.  What is meant by "self sealing" is that, upon inoculation and subsequent removal of the syringe needle, the hole used for inoculation closes itself, as opposed to the previous method of having to cover the hole with tape or other filtration media.  Lids of this nature are typical for liquid cultures, but can be used in almost any mycological application where filtered lids are required.

The list of supplies for this project includes:

                        1. Ball disc lids, size matched for the jars you will be using.          
                        2. Tyvek Scraps
                        3. Band-Aids
                        4. RTV High Temp Silicone
                        5. Tin Foil Cooking Tray
                        6. Drill Bits

Additional Items Used in this Particular Demonstration were a common household strainer and a "Helping Hand" combination magnefier and clip, available wherever solder can be found.  As far as the drill bits go, 3/16" and 5/16" are not set in stone, use whatever you prefer.  The only catch is that the hole for the innoculation needs to be big enough to accomodate the needle on the syringe.

Step 1:

Take your lids, remove them from the package.  Keep them stacked in the manner that they come.


Carefully drill two holes on opposite sides of the disc lids.  Go slow, as this will prevent flexing and tearing of the lid, and promote a clean hole.  A glove or rag is recommended, as the lids tend to heat up if you are going slow enough.  For my lids, I used a 5/16" drill bit for my breather hole, and a 3/16" drill bit for my innoculation port.  You want to make sure your innoculation hole is big enough for your needle, but not so big that it's difficult to plug with the RTV.



Once that is completed, take your lids inside, and run them through a strainer under some water to remove any lingering metal or wood fragments from drilling.


Here is a picture after the rinse of the lids layed out and dried.  You can use a towel to dry the lids.


Looking closely, we see that sharp edges have been left from the drilling process.  We must remove these edges, as they pose a risk of puncturing our tyvek filter.  Two spoons can be used, or really anything.  Given the thiness of the lids, it is really not a difficult task.  The black arrows below highlight the edges to which I am referring.  If you can run your fingers around the holes without getting cut, they are smooth enough.


Here is a pic of the lids prepped and ready to go:


Next, take the metal tray and slice 12 holes in it, as shown in the below picture.  If it is not possible to find these, any type of clamp can be used.


Great, now put that aside until a little bit later.

Cut 6 bandaids as shown below.  The picture represents the stages taken to get to the finished product.  When finished, you should have 12 squares, with thumb tabs.  Be careful to leave the paper backing, as they are a pain in the ass to pull apart if you cut it off.


Next, cover your holes with round tyvek pieces, as shown below, followed by the square band aids we made in the previous step.  A single layer of tyvek followed by a single bandaid is sufficient.  Too much will prevent air flow, and we can't have that!  Make sure you are covering the larger of your two holes with this filter layer.


Next, take your RTV and put a blob big enough to cover the smaller of the two holes on both sides, as shown below.  For those wondering why I use RTV as opposed to the regular silicone that can be found at the hardware store, it's because A) RTV is used for engines, which happens to be another of my hobbies (thus I already have it around), and, more importantly, B) It can withstand an intermittent temperature of up to 650 degrees farenheit.  This assures that it will not fail in the pressure cooker.  The regular silicone had not discussion of a heat rating, so I decided to be safe, rather than sorry.


Once that is complete, your sealing ports should look similar to the picture below.  Don't worry about how it looks, we will take care of that later.


Enter the tin foil tray we sliced earlier.  RTV Silicone takes 24 hours to completely cure.  Use the tray to hold the lids while they dry, as illustrated below.


After waiting at least 12 hours, cut off the overdrip from the RTV so that you are left with a flat plateu, as shown below.  Although RTV will dry with a hardened layer in about 20 minutes, be sure to wait at least 12 before circumcizing the RTV, or else your scissors, scalpal, etc will be covered in RTV.


  Congratulations!!! You're done!!!  A few things to remember though:

    A)  You cannot shake jars using these if you are working with a liquid culture.  The Liquid will soak the tyvek, and it will act like a wick for airborn particles, including contaminants.

    B)  Remember to be swift in movement when it comes to removing the needle from the innoculation port, as this will reduce the time that the hole is
          stretched open.

                 - GoodbyeOrb

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