About a step in pouring plate

[dttom]

My routine practice is, after preparing the molten medium, I flame the neck of the bottle before removing the lid, then I pour the medium into plates with the plate-lid partially open, and I pour plates stack by stack.

However, I am taking a lab course now, and the lab manual tells me to pour one plate each time, and open the lid completely while pouring in medium. In this case, one additional step comes in, that is, after pouring all the medium, the medium poured in the plate is flamed before letting them set. The tutor asked for two reasons to account for that. Because the lid is completely removed and plates are poured one by one, the whole process is performed rather slow and allows more chances for contamination, I could think of one reason that it helps kill comtaminants that get in in the prcoess, but got no idea of another one, could anyone help? Thanks.

Edited September 3, 2010 by dttom

[CharonY]

Well there are different ways to pour and different reasoning for them, depending on amount sterility needs etc. Some of which really make sense, some less so. What I used to do is to pour stackwise, which is possibly the same way you do. I.e. one hand has the whole stack plus the bottom lid slightly lifted, pour, put lid back, continue with the rest of the stack.

Now to your question I have not heard of flaming the media in the dish as a routine method, especially as there is a risk of melting the plate. However in courses it is sometimes done when pouring was so slow that some of the agarose started to harden, creating lumps.