Things I’ve Learned

Six months ago I bought a bunch of lab equipment and took up yeast ranching. At this point it’s almost a parallel hobby on its own that happens to be connected to my interests in baking and brewing. I have learned a lot in these six months so it seems appropriate to share. Hopefully this will help those just starting out. Many thanks to Dmitri from BKYeast, Samuel from Eureka Brewing and jaapie for their help and suggestions.

  1. Use a jeweler’s scale for weighing out your ingredients for media. My regular kitchen scale was only accurate down to one gram, and even then it didn’t seem particularly accurate weighing small amounts. I had a lot of problems weighing out agar in particular, which is one of the more expensive ingredients. Using the right amount will help prevent you from making mushy or hard media.
  2. Malt-based media only need a tiny amount of malt extract. BKYeast suggests around 1.002 gravity wort. My last malt plates used only (I think) 2 grams per 100mL and yeast grew just fine on them. Using stronger wort makes it harder for the agar to solidify. I had to use twice as much before and still had a strange consistency. So, save your DME and agar.
  3. Potato-based media are cheap and easy and work well. Unlike malt extract media you can change the sugar, which lets you try to select for certain bugs.
  4. Prepare your medium in a flask, sterilize it and then pour into sterile plates. This is the standard way of pouring plates. I instead started using the method some homebrewers recommend, which is to pour the plates prior to sterilizing. I figured this saved me from having to open the plates in my kitchen and thus helped prevent contamination, but what happened instead was that media seeped into the sides while boiling, and this caused mold growth in storage.
  5. Plates will dry out, so store in a plastic Ziploc bag. I store them upside down and taped shut inside the bag. Lately I have stored them in the fridge until I am ready to use them. This also applies to incubating plates. Incubate upside down and inside a bag. Keeping them upside down keeps stuff from falling onto the media on top of the desired bugs.
  6. Even inside of a bag the plates will dry out, at least in the fridge. So, store your desired yeast strains in slants that you can tightly seal. After a few months the plates I had stored inside a tightly sealed bag in the fridge had dried out colonies and media, while an older slant was fine.
  7. It is possible to separate yeast from bacteria from a mixed culture at home. I had read something on a forum indicating that it’d be foolish to try this without antibiotic media, but even using standard media I have isolated yeast from mixed cultures like my sourdough starters.
  8. When preparing yeast for a batch make two in parallel or at least do it well in advance, because things can go wrong. I ended up brewing a batch with a contaminated, slightly sour starter. I got lucky and got clean beer out of it but don’t count on that!
  9. It can be hard to tell when a yeast colony is contaminated with bacteria without a microscope, so if you end up with sour starters it may be the slant or plate at fault, not the step-up technique. That’s what led me to get the contamination mentioned in #8.
  10. Glass plates are nice in that you can reuse them, but now that I pour plates the correct way I’m strongly considering switching to sterile plastic plates. For one thing, if you get something suspect growing inside you can just toss the plate without having to clean it up.
  11. It is easier to use an inoculating loop than a needle for streaking. I switched after watching a few YouTube videos where they only used a loop. The needle scratched the media more and provided no benefit that I could tell.

I think that’s it for now. I may amend this post if I remember anything else.

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