Media

How to make media

There are two types of media out there: agars and broths. Agar media requires heat to fully go into solution and will become solid when cooled. Broths do not require any heat and will stay liquid no matter the temperature.

To make media, first gather all your required ingredients, including reagents, weigh dishes, scoops, and bottles. Reagents are kept in alphabetical order on the media shelf. Weigh dishes, paper, scoops, magnetic stir bars and stir bar retrievers are kept in the drawer below the scale. Typically, we use screw cap bottles that are 1000 ml or less, but we also have various sized Erlenmeyer flasks available. Bottles and flasks should only be filled to a max of half the total capacity (e.g., a 1000 ml bottle should only have 500 ml worth of media inside it), as the media will boil during the heating and autoclaving processes.

Weigh out your reagents and pour them into the bottle/flask. Add the necessary amount of distilled water into the bottle/flask and swirl to get as many reagents into solution as possible. Broths can be autoclaved after this step, but agars must be melted into solution first.

Media can be melted into solution using the hot plate or using the microwave. In both cases, melt any agar-based media fully into solution prior to autoclaving. To determine if the media is fully melted, hold the bottle up to the light and look through it for any small clear blobs or distortions floating around in the solution. It helps to gently swirl the bottle first to agitate any unmelted agar but not so fast that bubbles develop.

Using a hot plate

Hot plates are slower to heat up but do get very hot.

Before starting:

• You will need to add a stir bar.
• If you are using a screw cap media bottle, use a small stir bar to compensate for the indention cavity at the bottom of the bottle. A medium or large bar will continuously bang into the bottle, resulting in less efficient stirring and a large amount of noise.
• If you are using an Erlenmeyer flask use the bar you feel is most appropriate for its size.
• Make sure pressure can escape your vessel while minimizing water loss
• If you are using a screw cap bottle, make sure your lid is loose enough to freely jiggle.
• If you are using an Erlenmeyer flask, set a glass funnel in the opening to allow pressure to escape and to prevent water loss.

While using:

• Do not start at the highest setting.
• Keep a close eye on media with sugar to avoid caramelization at the bottom heat at lower temperatures to start.
• Each hot plate is from a different manufacture so exact settings will not be the same for each unit but I suggest not going over heat setting 6 on any of them.
• Avoid allowing the media to boil.
• Once melted into solution remove the funnel and/or stir bar then cover with aluminum foil.

CAUTION:

• Never leave hot plates unattended. If you need to step away, even for a moment, turn the heat off but keep stirring.
• Should media boil and spill, clean up as soon as possible.

Using the microwave