Plating Results

Well, it looks the book I use for media preparation was right! Seriously guys the “Handbook of Microbiological Media” by Ronald M. Atlas is a MUST have reference for anyone who’s making up any kind of medium, and especially for home yeast ranchers since it includes recipes that can be made from your every day around the house materials. One such recipe is the Potato Dextrose Agar which goes something like:

Potato Dextrose Agar Composition per liter:

Potatoes ………………………… 300.0g

Glucose …………………………… 20.0g

Agar ……………………………….. 15.0g

Preparation of Medium: Dice potatoes and place in 500.0mL of boiling water for 30 min. Strain through cheesecloth. Adjust volume to 1.0L with distilled/deionized water. Mix thoroughly. Add agar. Gently heat and bring to boiling. Add 20.0g of glucose. Mix thoroughly. Distribute into tubes or flasks. Autoclave for 15 min at 15 psi pressure @ 121°C. Pour into sterile Petri dishes or leave in tubes.

Use: For the cultivation and maintenance of numerous fungi such as Cephaleuros virescens.

I modified the recipe a bit by adding sucrose (table sugar) instead of glucose to allow for Lactobacillus differentiation. Lacto grows as small colonies on other media, but sucrose allows it to form large colonies due to some complex formation that I don’t remember off the top of my head. So the plan is to seed a mixed culture such as that Berliner I’m currently playing with, or a culture from grain, or Cascade dregs (their Lacto strain is a damn monster based on how sour the beers come out) on Malt or something else, pick out small colonies and streak on PS plates. Unless my books are wrong, Lacto colonies will get big. Another route would be transfer the entire plate onto a filter/membrane/paper, transfer onto a PS plate and compare the growth.

I also read that this medium is very good for mold growing and boy were they right! Mold contamination is not that uncommon, but it takes a while for it to grow out to be a problem. By then you’ve grown whatever you need and you don’t care about the mold. It appears that this is indeed an ideal mold growing medium. I have never seen such rapid growth. Never! It’s just so cool that I’m not even mad about the plate being all but useless now.

Another good piece of news is that all four plates grew colonies and I started further propagation – transferring individual colonies to their own plates. The Berliner (from the original WY pack) plates seem to have colonies with 4 different morphologies. Flat smooth-edge white colonies (Saccharomyces I think), round smooth-edge beige colonies (could be Brett), rough-edge round white colonies (could be Brett), and pin-prick white colonies (could be Lactobacillus). According to WY there should only be 3 organisms there so what I see on the plates in terms of smooth vs rough/white vs off-white is probably due to agar scratching.

Also it looks like the other plates from that batch turned out fine. The agar is nice and firm so it must have been the uneven mixing or something else… don’t see how though, because I made sure I mixed it well to avoid this problem. Hmmm… Regardless, the experiment goes on!

Here is a photo of the really moldy plate. Appreciate the beauty of the mold! Seriously, I find mold to be just fascinating. I even looked into getting a Mycology degree, but there aren’t any in NYC so I ended up in Molecular Bio instead and I don’t regret it.

Appreciate the mold! As you can see, the colonies also grew out nicely but got overgrown.


That much mold in 48 hours is just amazing. It's also amazing that a 7 month old culture grew so quickly.

5 thoughts on “Plating Results

  1. Potato dextrose agar is what we used for mold identification. It allows really good sporulation. Mycology is fascinating and mold id was one of my favorite tasks. The mold you have looks like one if the few I have issues with when doing plates at home. Nice work!

  2. Well is the yeast ranching master himself complemented me, I must be doing something right!
    Thanks a lot, Roffy, for the complements, and especially for the advice you’ve given me.

  3. Pingback: #5 Agar plates (Kombucha) | Eureka Brewing

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