How to make solid culture medium plates for yeast culture

You will need several 100 mm borosillicate glass pyrex (lab-grade) petri dishes which can be purchased from Amazon, along with lab-grade pyrex Erlenmeyer flasks of appropriate size for the quantity of plates that you want to make.  Here I am using two pyrex petri dishes and two small Erlenmeyer flasks, since I am only making two plates and a small slant (50 mL).  If you want to also make slants, then you should purchase borosillicate glass 'slant tubes' with screw top.  Also, some other microbiological instruments like a spreader and inoculation loop could be helpful.  I made it at TechShop with some scrap metal, pliers, and a vise.  www.techshop.ws 

You will also need the raw materials that will make the solid culture medium.  You can obtain laboratory-grade materials from Amazon, or you can make your own 1.040 wort and use yeast nutrient and agar-agar to solidify the plates.  You can buy D-(+)-Maltose, Peptone, yeast extract, and agar technical (solidifying agent) on Amazon, believe it or not (autoclave the maltose separately to prevent caramelization of the sugar).  While this method produces solid growth medium that is perfect for keeping yeast in a laboratory setting, many folks don't want to shell out the dough for these materials, and prefer to make use of beer-making equipment and materials they might have at home already.  

The easy way to do this is to get agar-agar (solidifying agent similar to gelatin) online or at an Asian food store.  Then, make a simple 1.040 gravity wort using only brewer's 2-row base malt, add yeast nutrient and 20 grams of agar-agar into 1 liter of culture liquid (can be scaled down accordingly depending on your needs), and autoclave in an appropriately-sized Erlenmeyer flask (you don't want to exceed about 50% of the volume of the flask when autoclaving).  Personally, I don't have a pressure cooker capable of autoclaving my 2 liter Erlenmeyers upright and full of liquid, so I make small batches.  You can easily make up 1.040 wort and split into several batches (in mason jars) for autoclaving purposes, and these will keep in the fridge or basement as long as they are sealed.  Then, you can use this liquid for starters or 50-100 mL at a time for making solid culture medium plates such as we are discussing.  In this case, you would take 50 mL of this nice pre-autoclaved wort and add 1 gram of agar-agar to it, dissolve, and autoclave again in an Erlenmeyer flask in your pressure cooker.  

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