We use canning jars for a variety of purposes. Two of those purposes include agar (i.e. Petri replacements) and grain inoculation. When using jars, we usually need to use lids with a small amount of air exchange.
We have tried both the metal lids and the plastic lids with jars.
- We prefer using the plastic lids over the metal lids
- The medical tape (2 pieces, one perpendicular to the other) works well with the plastic lids
- The plastic lids are very easy to twist on/twist off, making work in front of the flow hood faster
- As the plastic lids are easy to take off, they can become loose in the pressure cooker. This is a risk
- The medical tape needs to be smoothed down before using the lids – it also comes off fairly easily
- The holes are easier to drill in the plastic lids than the metal lids
- The metal lids stay on in the pressure cooker, there is no risk of them twisting loose
- The metal lids rust over time. They must be inspected before using them
- When using the metal lids, we prefer using the poly-fill in the hole(s). Make sure it’s tight in the hole, otherwise you will get unfiltered air exchange.
- Plastic lids are more expensive to buy than the metal ones
If you are using the metal lids, drill holes with a drill press. Keep the metal discs in their cardboard box and drill a hole (or holes) through the entire box. That way you only lose one metal disc to rough edges.
There is a warning on the box that the plastic lids are not to be used for canning. That is true! However, since we drill a hole in the lid the pressure does not build up in the jar. We have successfully used the plastic lids many times in the pressure cooker.