How the yeast bank came about

Now everyone knows of the drawbacks of maintaining yeast on slant. It's a hassle to make up a starter; make a little wort, flame your loop, drag out a sample of yeast, innoculate the wort, let it grow a few days, add this to a 10x quantity of wort, then repeat, repeat, repeat, etc. You open it up every few days for a week or more, exposing it to possible contamination every time, and finally you have enough to pitch after a week or 10 days. A regular pain in the butt. I figured there must be a better way.

So, I acquired some screw cap test tubes, 4 oz, 8 oz, & 32 oz canning jars, made up some wort, and pressure canned it. I made some tubes with 1 ml, some with 10ml, 4 oz & 8 oz jars with 100ml, and 32 oz jars with about 600ml. At least now I didn't have to make up the wort each time I needed some. This did make it easier, but it still required planning 2 weeks in advance of brewday. I needed a little more freedom to be (somewhat) spontaneous in my brew schedule. And I still had to deal with reculturing unused strains every 6 months.

Then I acquired a stir plate, and heard all the wonderful things about being able to produce 6-10 times the yeast with the same amount of wort, and my head started spinning. I figured that if a stir plate makes yeast grow that much faster, then out with the old 10x rule. After all, the rule was intended to allow yeast to outcompete any other beasties to minimize contamination. If they grow that much faster with a stir plate, then why not go from 5ml to 1000ml all at once?

So I tried it. And, it worked fine! The 1000ml wort was totally consumed in two days, and there was over a 1/4 inch of pure slurry in the bottom (after chilling overnight) of my 2L erlenmeyer flask. Now I modified my process a little more, and it was even easier, but a little more expensive. I began adding the 4ml wort to the slant, then 2 days later pouring it into the 1000ml wort, dripping the last teeny, tiny drop into a new slant for reculturing. Voila! a pitchable quantity in 4 days from slant! So I pressure canned some more tubes with 4 or 5ml wort and brewed on, and every time a yeast was used it was recultured. However, it was now costing me about a buck every time I used yeast.

Bear with me, I know this is getting lengthy, but I'm almost done. I decided I needed to start making my own slants. I needed a little help with this, and since my other ranching buddy happens to be a microbiologist who grows bugs for a living, he was naturally the one to turn to. We researched growing media and making slants, talked 9 others into joining the project, bought 1000 tubes & caps, and made some agar slants - a whole boatload of 'em. Lucky we had access to a lab, where we could do 500 at a time. The initial purchase of all the materials cost about $.30 per tube (80 slants each club bank, 40 slants & 36 wort tubes per person for about $28.00 each), and when they are empty and we reuse them to make new slants, the cost will be rock bottom, about 2 cents each. And we can do them in smaller quantities in a pressure cooker.

How I make the slants

In order to make the slants with agar nutrient, you will need a test tube rack of some sort, a pressure cooker, and a method of measuring and dispensing small quantities of solids & liquids (single digit grams & milliliters).

Instructions for making 100 slants, 3-4 ml each:

    Ingredients:
  • 400 ml water (low carbonate)
  • 10 gr DME
  • 5 gr Agar
  • 1 gr Yeast Nutrient
    Steps:
  • Mix water, DME, & yeast nutrient; boil vigorously
  • Strain thru filter funnel, add agar, reboil
  • NOTE: Agar starts to set as it drops below about 45C. Try to fill and cap all tubes before this occurs.
  • Add 3-4 ml to each slant and loosely screw on the caps

DISCLAIMER: Pressure cookers are dangerous! This process works for ME using MY pressure cooker. Use this process at your own risk!

Now you will need to pressure cook (autoclave) them. My cooker is the type with a pressure gauge. Its instructions say to heat until steam starts escaping from the valve, wait 15 minutes, close valve and take it to 15psi, wait 15 minutes, then turn off. This will result in a mess, as the agar will boil over and the tubes will be near empty. What I did was to modify the process to simulate the process in an autoclave:

I use low carbonate or distilled water to avoid carbonate buildup on the outside of the tubes

What I do is to add about an inch of low carbonate water to my cooker and preheat it to about the same temp as the slants (50-60C). I place the rack into the cooker at about a 30 degree angle so that the tubes are an inch or more above the water. I seal the cooker, and begin heating. The pressure will start to build before the boiling point is reached, hopefully keeping the agar from boiling over, and when it reaches 15psi, I maintain it for 20 minutes. I turn off the flame and allow to cool to the touch before opening (just wait overnight). Then open and screw the caps on tight.

Alternatively, you can put the tubes upright to help avoid possible boilovers. When the cooker has cooled down, but is still above 45C, the media will still be liquid. You can then set the rack at the desirable angle PREFERABLY in the cooker or other sanitary environment, replace the lid and let cool until set. Then tighten the caps. Store in a cool place (fridge is best).

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