Eureka, the banking journey goes on. The introduction to yeast banking and background of this particular post can be found here. Lets proceed with technique number three, banking yeasts on agar slants. Method number one was banking yeasts on agar plates, the second one banking yeasts in sterile solutions. Banking yeasts on agar slants is very similar to the agar plate method. However, has less disadvantages than the agar plate method. Lets have a look at the method.
Description of the technique
Agar slants are basically tubes filled with agar media (Fig 1). When you prepare agar media for plates you can use the same media to prepare some slants. After the agar media cooled down the media stays gelatinous. You now can streak some yeast colonies on the agar in the tube, seal the tube and leave the tube at room temperature for some days until colonies on the agar appear. If colonies appeared, the agar slant is ready for storage. Simple as that.
– Tube or any other containment containing the agar media. Make sure you chose a containment that can be tightly sealed (with a cap etc.)
– Agar media (see post about agar plate method)
– Source to get the agar slants sterile (for example a pressure cooker)
1. Prepare your agar media. Best would be to mix all the components for the agar media together and heat it up a bit until the agar agar is dissolved. Agar agar is not very soluble at lower temperatures and has to be dissolved at warmer temperatures. Just heat up the whole agar media (malt agar for example) until the agar agar is dissolved and then proceed to step number two.
2. Fill your tubes (or any other containment) with the freshly prepared agar media. Seal the containment and sterilize them in a pressure cooker if possible. Let the tubes sterilize for approximately 15 min. You could even submerge the tubes in boiling water for 15 min.
3. Cool down the slants. Lay the tubes sideways to get the liquid surface as shown in Fig 1. This makes it easier later on to streak some yeasts on the agar media. Wait until the agar cooled down to room temperature.
4. Store of streak. The agar slants are now ready to bank some yeast. Or can be stored at room temperature or in a refrigerator for later use.
Bank the yeast
Just pick up a yeast colony or yeast slurry with a sterile inoculating loop and streak the stuff on the agar slant. The process is very similar to streaking some agar plates. If you need further information about how to streak agar plates or slants, please have a look at the agar plate post.
Store the agar slants in the refrigerator (not in the freezer). You could even store them at a cold, dark place.
Please refer to the agar plate post reanimation process.
My experiences with this method
I have to mention, I do not have a lot of experience with agar slants. I just tried it once to store yeasts for some weeks and use it to ship yeasts. I therefore can’t tell you how long you can bank yeast with agar slants. However, this is a widespread method to store yeasts. Some advantages/disadvantages of this method relative to the others I described:
|Rather easy method||Yeasts can overgrow agar media|
|Not a lot of equipment necessary||Contaminations happen|
|Contaminations can be visible||Can’t store yeast mixtures, blends|
Let me talk about the advantages first. This is a rather easy way to bank some yeasts. You just need some tubes, agar media and an inoculating loop or any other sterile gadget to get the yeasts on the agar media. Please have a look at my agar plate post to see what equipment you could use. Second, if any contaminations happen on the agar media you might see it. However, not every contamination has to be visible. And at last, you can easily trade some yeasts with other homebrewers. Just streak some yeast on an agar slant and either wait until colonies arise and then ship or ship right after streaking.
Disadvantages. Again, with agar media the yeasts still grow. Sooner or later the agar media is overcrowded with yeast colonies. This does not occur every time. And does not have to be bad after all. Its how you look at it. I do not like overcrowded agar media. I like to see single colonies… Second, because nutrients are in the agar media other yeasts, bacteria can grow as well. Contaminations can happen. Well contaminations can always happen. Independent of the yeast banking method you choose. It is therefore really, really important to keep the yeasts away from any contaminations.
Concerning agar slants as a long-term storage method. I do not have any long-term experience with this method. Please let me know if someone out there has any long-term experience with this method. I would not be surprised if you could use agar slants to store yeast for months or even years. If long-term storage (months to years) is the main goal for you to get into yeast banking, please have a look at the sterile solution method or the next post which is about a frozen yeast library.
I have to mention again, this is not a method to bank yeast mixtures or any other mixtures, blends etc. Since some growth still occurs, the ratio between the yeasts, bacteria etc. will eventually change. Even if the ratio of the mixture stays during the storage, it could change again as soon as you recover the mixture… The only way to store mixtures is to separate the individual strains and store them separately.
To summarize. Banking yeasts with agar slants is very similar to banking yeasts with agar plates. A main difference here is the lower risk of contaminations and dehydration because agar slants are tightly sealed tubes (or any other sealed containment).
The next, final post in this series is about a frozen yeast library. This is in my opinion the only way to store your yeast for a longer period of time. Stay tuned!