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Modifying Metal Jar Caps
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| Polyproplylene plastic caps, called "B-Caps"
(left) and made by the Magenta Corporation, and be used in a microwave oven and a pressure
cooker. They are the preferred cap to use on a baby food jar tissue culture, but they are
expensive. If you have a pressure cooker, you might consider using modified metal caps
(right). Note that PhytoTechnology Labs now makes a similar caps, PhytoCap. See their website for pricing: www.phytotechlab.com |
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| Air exchange is necessary for healthy plant growth. This can be accomplished by making a hole in the top of the cap and sealing it with a bandaid. Using a nail or a Philips screwdriver and a hammer, with a piece of scrap wood underneath, punch a hole in each metal cap. |
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| Pound down the sharp ends on the inside (far right). Some have reported problems with rust formation on the inside of some of the caps. Inspect the caps before using each time. The rust could get into the media and cause a problem with plant growth.
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| Place a round waterproof bandage ("3M Active Strips") over the hole on the outside of the cap. This will keep your cultures sterile and allow necessary exchange of air. These bandaids will hold up through pressure cooking many times. |
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| Other jars can be used for plant tissue culture. The best seem to be Smuckers jam jars (medium size), marmalade jars, olive jars, and others of a similar structure. |
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| The metal caps on these jars can be modified as described above. |
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| Metal caps can only be used if you
sterilize your jars with a pressure cooker. The metal will destroy your microwave
oven. Only use plastic or polypropylene jar caps in the microwave oven. Do not use the white plastic pint jar covers (far left) in the
pressure cooker. They will melt (see below). |
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Many thanks to Larry Evans, Joyce Miller, and others who brought this information to my attention. |
Which cap is safe for each sterilizing method?
| Type of Cap | Safe for Microwave? | Safe for Pressure Cooker? |
metal |
NO | YES |
polypropylene Magenta B-cap for baby food jars |
YES | YES |
white plastic (comes with kit) |
YES | NO |