Boiling agar

Discussion in 'Supporting Biology' started by BioBee, Feb 28, 2020.

  1. Hi folks, just a quick one.

    Does agar always need to be made up cold and then boiled or can I add boiling water to the powder?

    It is for a DC Pip diffusion experiment so it will not need to be sterile or anything, I am, as such simply using agar powder and not nutrient agar.

    Of course I make it properly for microbiology expts but I was just thinking of saving a bit of time.

  2. If you don't autoclave it, it will be more cloudy than you might desire. It usually reduces clumping if you start from cold, as well.
    BioBee likes this.
  3. Probably will work if you stir constantly whilst adding the boiling water - but just try a sample and see
  4. I've started using boiling water in all cases - saves a bit of time. I'm not sure if its the wrong or right thing to do, but it works for me! Do make sure you bring the agar to a full rolling boil still to ensure it sets though.

    A useful tip I picked up was to designate a kettle for distilled water only then you can have hot distilled water whenever. Always put hot water in my autoclave - speeds up the process there too.
    Last edited: Feb 28, 2020
    Jaytee likes this.
  5. I always use boiling water then I put it in the autoclave -it's going to boil in there anyway! Never had a problem with doing it this way.
  6. I always use a heated magnetic stirrer anyway but I understand you can use a microwave so perhaps boiling water and stick in a microwave if not clear , stir occasionally until it does clear.
  7. Cheers folks! Just tried it and it worked a treat. I've to do more on Monday :) I'm glad that this agar doesn't smell as bad as the nutrient stuff haha
  8. It doesn't need to be crystal clear anyway, the first batch I made ended up cloudy but it was still clear to see the diffusion through the cube. Very bizarre looking, like a blue tesseract!
  9. I always think technical agar smells worse than nutrient agar! Technical agar is by nature much cloudier than nutrient agar - it won't go clear even when boiling.
    BioBee likes this.
  10. or microwave on defrost or lower for 15 minutes.

    it wont go clear but you should not see lumps on the glass.
  11. Use a glass rod to stir as shows up the lumps left better than just trying to look through solution.
  12. Thanks all, I think i've got it down pat now, just made about 60 ice cube sized lumps and a dozen larger blocks. Also using the spare to test some ideas for science club things.. but I'll make a post about that on its own ;)
  13. Hi BioBee, we've done this practical with Cresol Red but DCPIP sounds better to me. What quantities/concentrations did you use?
  14. Hi there, I can't remember exactly but for 400ml agar it was 10g of agar and I think 0.07g of DC Pip. Ascorbic acid was made as a 10% solution which gave a rate of about 10 minutes for a 2cm x 2cm cube to turn from completely blue to completely 'clear'. Of course if you want it to go faster or slower you can change the amounts of DCPip or ascorbic acid.

    I find it works brilliantly with phenolphthaline which was (for 400ml again) 10g agar then half a small spatula of sodium carbonate and a few drops of phenolphthaline to give the colour. then the agar would be dipped into a acid to discolour. I will be testing it the other way around too, adding some acidic powder to the agar so that it remains colourless when set, then dipping it into a basic solution to then turn pink.
    Snailo likes this.