There are several ways to store pure yeast for future use, as well as propagating yeast from the storage media or store bought beers. What you will need:
Propane torch or bunson burner (you perform work below the flame - as the flame keeps the air rising and kills any bacteria that would fall on your growing media/agar)When you receive your yeast pack, sanitize the pack by placing in iodophor solution. Clean your hands with an anti bacterial soap making sure not to handle anything other than what you are working on as far as the yeast is concerned.
Be extremely careful when working with a propane torch or bunson burner - failure to exercise extreme caution and common sense may lead to severe burns, property damage or death. Make sure there is adequate ventilation, without creating any drafts (which should be avoided to prevent the storage media from becoming contaminated)
Make your slants by boiling the agar/yeast nutrient mix with the recommended amount of water, and filling autoclavable test tubes. It is a good idea to use some empty clean cans (from canned food) to hold the test tubes. Fill the tubes 1/4 to 1/2 of the way full. Place the lids on the tubes loosely. Place the cans of test tubes in our pressure cooker, and pressure cook according to your pressure cooker directions for canning food. It is a good idea to make sure the media is acidic enough to prevent botulism spores from forming/reacting. The media should be below 4.6PH. This also helps prevent many types of bacteria from forming on the media (makes it more resistant to growth of bacteria)
Use a digital ph meter and compare against litmus papers if possible. It's a good idea to get two independent results just in case their is a variance. Autoclaving in a pressure cooker sterilizes the media, and also destroys any botulism spores present.
When you are done autoclaving the slants and they have cooled a little, tighten the lids to prevent bacterial contamination.
Perform the same job with the pyrex/duran perti dishes. Autoclave them in the pressure cooker. When you are done, pull them out without seperating the two dish halves. Special way tape is available to seal these plates from outside contamination.
Please note, if you house has a mold problem, it may not be wise to attempt to make your own media on slants or dishes.
If you notice any growth on your "sterile media" in your slants or dishes, then your sterilization procedures failed and the contaminated media should be disposed of promptly, and in a safe manner.
When you are ready to use the media, perform all work closely under a flame source, such as a propane torch (making sure the torch or burner is mounted in a stable way that it cannot fall over). Heat the innoculation loop until it glows red. Place it in your liquid yeast and swirl, then carefully open the lid on your slant just enough to get the loop inside, and drag the loop across the surface of the agar. Remove the loop and close the lid tightly on the slant. Store slants in a brown bag at room temp (70F) for a 3-7 days until you see a layer of white yeast on the top of the agar. Place bag in the refridgerator - yeast can be stored for several months this way.(Repeat for multiple slants).
To use the yeast cells on the slant, follow the same sanitary procedures, working closely under a flame, flame the innoculation loop, open the top of the slant just enough to get the loop in, then let the loop cool on the wall of the slant for a minute or two before innoculating it with your pure yeast from the slant. Remove loop and place it in a test tube (you prepare earlier) that has been autoclaved with wort & yeast nutrients inside of it, and cooled to room temp. Swirl the loop, remove loop, screw top on tube and shake vigourously to aerate. Unscrew cap slightly to allow co2 to escape tube during ferment.Store at room temp for 3 days, shaking twice a day and releasing any pressure that builds up (prevent explosion). Aim away from body when releasing pressure by slightly unscrewing cap slightly.
You will transfer the propagation test tube contents to a 500 ml pyrex flask that has wort in it you previously boiled & cooled. Shake to aerate. Place sanitized stopper & airlock on flask. Repeat transfers in 500 ml increments every 1-3 days (at the head of each ferment), until you have a suitable sized yeast starter (we recommend 1000 ml (or 1 liter) per 5 gallon batch. It is recommended to make the transfers during the vigorous ferments to minimize the lag time and maintain a healthy yeast starter. Be extremely careful not to leave flasks uncovered during these early stages of your yeast starter.
It is recomended you cover flasks with aluminum foil when boiling and cooling wort for your yeast starters, to minimize bacteria from falling inside the starter media (i.e. wort)
Petri dishes are used for seperating out single colonies. Usually, you innocuate the petri dish agar by making one line with the innoculation loop after you have dipped it into media containing yeast (like your yeast smack pack or WhiteLabs Tube). Then you flame the loop, cooling it down inside the partially covered petri dish - you can cool it by touching part of the agar you don't intend to use. Then, making a line from the original line. Do this several times, flaming the loop between making each line. What you are doing here is "diluting" the yeast, so that you are leaving single cells to grow and form perfectly round single cell colonies on the agar.
Close the petri dishes and seal with wax tape - let incubate at room temp for several days. We like to place the dishes in ziplock bags, pushing out all the air - tis helps to minimize contamination.
When you have sighted the single colonies, you are now ready to place them in storage.
Autoclave (pressure cook) several test tubes filled to the top with distilled water. Place caps on tubes, but do not tighten until autoclaving is completed. Tighten cap after tube begins to cool. Cool to room temp with lids capped.
Using sanitary procedures and working under a flame, flame innoculation oop, immediately placing inside of petri dish - let cool against glass wall of dish for a minute. Then, innoculate loop with a pure colony, remove lid on tube with distilled water, and swirl loop inside of distilled water to dislodge pure yeast colony. Make sure not to pick up any agar in this process. Remove the loop, top off tube with distilled water and cap tightly.
Now your yeast is ready for long term storage.
When you need to use the yeast - drain the tube except for the pure white yeast at the bottom. Use the same sanitary innoculation procedures mentioned in building a starter from a slant, but make a slant from the yeast that you placed in long term storage (distilled water) first.
Storage of pure yeast colonies in distilled water yields the same results as storage in liquid nitrogen - the yeast can be stored for years this way.
By learning the proper techniques to store & propagate yeast, you can amass a huge library of yeast from which to choose from, completely eliminating the need to purchase yeast regularly which will save you big $$$. We recommend making multiple slants from each yeast pack, and storing those in the refrigerator for future use - this will guarantee you pure yeast strains.
All yeast you store in this manner will have to be built up from the small colonies at first using a test tube with some wort (for a day or two), and then small 500 ml beaker for a few days, to larger beakers until you have a pitchable quantity of yeast.
The process takes close to 2 weeks, but if staggered with other batches you won't be "waiting around" for your yeast to be ready. This really is a great way to save money and at the same time exercise full control of your brewing process. On top of that, the methods you learn to propagate your own yeast can also be used to propagate yeast from unfiltered, unpasteurized fresh commercial beer.
Gerhardt
