Potato Dextrose Agar

Potato Dextrose Agar

1 L water

300 g chopped fresh potatoes

20 g agar agar

10 g dextrose

2 g yeast/marmite/yeast flakes (optional)

1 g petone, soybean (optional)


*For liquid cultures use 4 g agar agar instead.


Combine water and potatoes in a large pot on stove. 

Heat to boiling and boil gently for one hour. 

Strain potato chunks for snack/compost and keep liquid part: "potato water", to make growth medium.

Add the dry ingredients to the potato water in a clean pot on stove. 

Add dry ingredients and amount of water to make up any water lost in straining.

Heat to near boiling to help dissolve the agar agar. 

Some undissolved components may dissolve/gel during pressure cooking in upcoming steps. 

Stir well before filling heat resistant containers for pressure cooking (flask to pour petri dishes/jars for liquid cultures):  This will ensure any undissolved components are evenly distributed.  Fill containers half volume max to prevent boil-over.  One litre will make 4-8 liquid cultures or 20-100 petri dishes depending on size and depth of fill.

Sterilize closed containers of medium for 20 minutes at 121 C at sea level in a pressure canner/sterilizer, according to the manufacturer's instructions.  Overpacked cookers or large volumes will require longer times.  Your goal is to fully sterilize without caramelization. During cooling when the pressure is between 0 and 1 psig move the cooker in front of a HEPA filter air source to finish cooling.