How do you make up 5% sucrose agar plate?

Question

I need to make up an LB-agar plate with 5% sucrose. My question is - do I add the sucrose solution to the agar mix before autoclaving, or after?

Answer 1

Sucrose is reasonably stable during autoclaving, so there's no problem. You can just make the complete medium and autoclave. If you'd need glucose or fructose as a sugar it's usually recommend to filter-sterilize a solution of this separately and add after autoclaving, as they would caramelize significantly during the autoclaving.

Answer 2

You risk contaminating the agar solution if you add the sucrose after autoclaving. In order to keep the agar as sterile as possible before pouring I would suggest making the solution up completely before autoclaving. Remember agar growth media have carbohydrates in so it is unlikely to be damaged by the heat. Heat can damage things but usually only if there is something for them to react with or they're proteins.