Yeast propagation made easy

One of the biggest problems faced by homebrewers in India is poor availability of ingredients. Specially Yeast.
This article shows you how to easily propagate yeast from a single gram of dry yeast or a tube of  yeast slurry.
You will never have to run around for yeast if you manage your own stocks.
Its a long post, but an easy process.

What you need

  1. Stir Plate - Buy this online. The cheapest one will do the job. You don't really need a hot plate on it. But its hard to find one without a hot plate
  2. Two Magnetic stirrer bars ( 3 cm ) - Any lab shop 
  3. Conical Flask ( 1 liter or 2 liters, larger the better ) - Online or lab shop
  4. 50ml Centrifuge tubes / Falcon Tubes / vials ( check the picture ) - Lab shop
  5. Sanitizer - Check my post here
  6. Dried Malt Extract - Buy it at - http://www.brewof.com/product/dried-malt-extract-dme/


Stir plate, Stirrer bar and Conical Flask

Dried Malt Extract
Falcon tubes







Propagation process


Starting yeast - 
Start with half a gram of dried yeast or a tube of yeast you created earlier using this process. 
Hope this was in the fridge. Take it out of the fridge and keep it at room temp. This will warm up until you finish the rest of the process.





Make a starter wort -

Volume = A little over half the volume of your conical flask, i.e 600ml for a 1 liter flask.
DME to water ratio = 1 is to 10. So use 60gms of DME in 600ml of water.

Be careful, this is very hot stuff. Have a towel handy.

Steps -
  1. Dissolve the dme in water making sure there are no lumps. Use a small pot for this.
  2. Boil the wort for 10 mins. Keep an eye out for boil overs.
  3. Turn off the flame.
  4. Sanitize the flask and a small piece of aluminium foil.
  5. Carefully pour the boiling hot wort in the flask. Try not to get the wort on the inner walls of the flask.
  6. Cover the flask with an aluminum foil and put in the fridge/freezer to cool it down to room temperature as fast as you can. Take care you don't freeze it.


Dissolve the DME
Boil the wot for 10 mins

Pour boiling wort in sanitized flask



Cover with a foil and keep in freezer


Start the Starter

From here on sanitation is going to be extremely important. Sanitize everything that is going to come in contact with wort. This will make sure you have many generations of healthy yeast.

Steps -
  1. Your wort is now at room temp, take it out of the freezer.
  2. To sanitize the stirrer bar, soak in sanitizer for a min. Sanitize your hands too.
  3. Quickly open the foil on the flask and drop the stirrer bar in the flask.
  4. If you are using a tube created earlier, shake it properly and add in the flask. If you are using dry yeast, add the dry yeast in the flask.
  5. Immediately close the foil.
  6. Put the flask on the stir plate.
  7. Make sure the heating on the stir plate is turned off.
  8. Turn on the stir plate. Keep on a lower speed setting at first. Slowly increase it until you see a small whirlpool in the center of the wort. You really don't need too much speed.
  9. In hot summers cover the flask with a wet towel. Keep changing the wet towel every now and then to keep the flask cool.
  10. Keep the starter on the stir plate for about 36 hours. 


Stir plate on minimum speed
Wet Towel in summer




The continuous stirring drives the CO2 out of the solution and keep the yeast in suspension. This ensures that the yeast multiples in a healthy environment.

At the end of 36 hours, you will have a very muddy liquid. The color will turn from dark brown to light brown. 


Concentrate the yeast

Steps -
  1. Use the second stir bar to drag the stir bar inside the flask to the top of the flask.
  2. Keep it in the fridge ( NOT the freezer ) for 2 days. 
  3. After 2 days you will see a thick layer of yeast at the bottom and clear liquid on top. We are ready to package now.


Stir bar on side and flask in
fridge for 2 days
Yeast at the bottom and
clear liquid on top after 2 days


Sterilize the tubes

We are going to store our yeast in the tubes, so we want to make sure they are sterilized.
Auto-clave the falcon tubes to sterilize.
Poor man's autoclave - a pressure cooker.

Steps -
  1. Fill a small cooker with water ( half the volume )
  2. Put the tubes and lids into the cooker.
  3. Close the cooker and heat until you hear 2 whistles
  4. Turn the flame off and let the cooker open on its own.
  5. Santize a bowl and a fork / pair of tongs.
  6. Use the fork / tongs to take the tubes and lids out in the bowl
Cook this for till 2 whistles

Use a fork to drain water and put in a bowl

Package the yeast

Steps -
  1. Take the flask out of the fridge. Make sure everything on your working surface is sanitized.
  2. Remove the foil and sanitize the neck of the flask.
  3. Carefully drain the clear spent wort on top in another container leaving all the yeast in the flask. Keep very little liquid on top the yeast.
  4. Rigorously swirl the flask to mix up the yeast and the small amount of liquid left in the flask.
  5. Fill the tubes with the thick yeast slurry.
Sanitize the neck of the flask

Drain the spent work

Swirl to mix up the yeast

Fill the tubes

Packaged Yeast !!!

Tip :

Taste the spent wort from that container. The spent wort is not going to taste very good. But if it tastes vinegary or too sour, you got an infection. Dump the starter.

Storing the Yeast

Label the tubes. Date, strain and generation. Everytime you use a tube to follow this process increase the generation number. More on this later.

This yeast can be stored in the fridge upto 4 - 6 months. Do NOT store in the freezer.
After 4 - 6 months make sure you follow this process to create a new generation of the yeast. ( see the last section )
Do not store it near the cold air vent in the fridge, sometimes it blows too fast and can freeze the yeast. If that happens, the yeast will die.

After a couple of days all the yeast would have settled at the bottom. Our aim is to get maximum yeast in the tube. You will improve with practice.

Concentrated yeast at the bottom 
Labelled yeast tubes



How to use

All the hard work will pay off now.

3 days before the brew day, we are going to create a starter out of one of the tubes and use the starter for the batch instead of dry yeast.

Use a starter calculator to calculate the volume of your starter.

Simplified volumes - 

Starter volume for a 8 liter batch - 500ml ( use 50 gms of DME )
Starter volume for a 19 liter batch - 1200ml ( use 120 gms of DME )


Steps - 
  1. Use the volume above and follow exactly the same process in the Propagation section all the way upto "Concentrate the Yeast" step.
  2. On the brew day you will have the flask in the fridge.
  3. At the start of the brew day take the flask out and keep it at room temp. By the end of the brew day the flask with the yeast in it would have come to room temperature.
  4. Now instead of pitching the dry yeast as we normally do, we are going to drain the spent wort on top of the yeast and pour the concentrated yeast at the bottom of the flask into the fermenter.
So basically instead of packaging this yeast you are using it to ferment the batch.



Cheating --

What happens if you forgot to create a starter 3 days before brew day ?
If you have 2 tubes which are not more than a month old,  shake and add the yeast from the tubes in a 8 liter batch and it will work just fine. But beware that older yeast will not work well.
This cheat method is only for emergency.


Next generation

The beauty of the this process is that you can keep repeating the process for several generations of yeast.

E.g. 
You started with a gram of dried yeast and created 4 tubes. 
Use the 3 tubes for 3 batches. 
From the last tube follow this process again to create the next 4 tubes. This is your generation two.
You can safely repeat this process upto 7 or 8 generations.

What more, you share these tubes with other homebrewers, and they can follow the same process.
This is really useful to store and distribute rare strains of yeast that are not easily available.


Further readings

What I have described above is a dummies guide to yeast maintenance. If you really want to understand what is happening behind the scenes, I high recommend reading further -

https://www.wyeastlab.com/yeast-fundamentals

https://byo.com/article/fermentation-time-line/

http://beersmith.com/blog/2008/06/18/beer-yeast-fermentation-and-home-brewing/

http://masterbrewerspodcast.com/064-yeast-fundamentals

https://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices


Resources


Lab shop in Pune - 

Radha Enterprises
Shop No 7 Mantri Corner,
Opp Sakhar Sankul,
26/3 Shivajinagar,
Pune 411005
Ph : 020-25536731


Conical Flasks can be found real cheap on Snapdeal - 

https://www.snapdeal.com/product/lab-gear-borosilicate-glass-conical/666391216107#bcrumbSearch:conical%20flask


Stir plate examples on Amazon - 




4 comments:

  1. Excellent reading & explanation! Well done!

    Co van den Raad,
    Centurion,
    South Africa

    ReplyDelete
  2. Great article!
    If you want to store for a long time the tubes, you can fill them with a combination of glycerine and yeast, and keep them in the freezer :-)
    I do it :-)

    Cheers from Spain!

    ReplyDelete
    Replies
    1. Hi Adrian.
      We had published a post long back on yeast banking. But I though it was a little complicated for the new folks.
      Here the link - https://www.indianbrewer.com/2015/10/yeast-harvesting-and-banking-made-simple.html

      Its very nice to have international audience. How did you find my blog ?

      Delete
    2. Hi!
      I'm homebrewer too, and I have a blog about homebrewing (https://cervezarudimentaria.wordpress.com/), searching info about "I don't remember what" (hahaha) finally found your blog, and I saved it in my RSS reader :-)

      Cheers!

      Delete

Please mention your email ID, if you have any queries, so I can contact you.