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Yeast Harvesting & Growing

This blog post is about the method I use for growing and harvesting yeast.

I first create the recipe that I will be brewing so that I know the OG of my brew.
I also get the manufactured date of the yeast I have purchased as that will allow the calculator to calulate the viability of the the yeast thus the current yeast cells. Typically for liquid yeasts at the date of manufacture is around 100 billion cells, Imperial are 200 billion cells. In terms of harvesting I always intend to overgrow 100 billion cells and harvest that amount although I don’t measure cell count I use the calculator to estimate the millilitres to harvest which should give around 100 billion cells.

The calculator I use is here An explanation of each input:

Your Wort Details
Target Pitch Rate: My rule of thumb here is (OG) below 1.060 go for Ale – .75 million/ml and above 1.060 go for Hybrid – 1 million/ml
Batch volume: This is in gallons so for ease 15L = 3.30gallons, 19L = 4.18gallons, 20L = 4.40gallons & 23L = 5.06gallons
Original Gravity: That is the OG of your recipe
Overbuild Cell Count: I set this to 100 because that is typically what is provided by the yeast manufacturers
Yeast Cells Needed: This is calculated by the website and is the number of cells required for your recipe + 100 billion cells for the harvest

Your Yeast Details
Initial cell count: This is the yeast you have bought or the harvest from another WHBC yeast bank member. For the benefits of the WHBC yeast bank I would suggest we always overgrow 100 billion cells so we can always enter 100 in this cell. For purchases yeast then the packet or the manufacturers website should always state the provided cell count of their yeasts.
Production Date: This is the manufactured date on the yeast packet or provided from the the WHBC yeast bank member. Some White Labs packets don’t have the manufactured date on them but if you take the Lot number from their packets and enter the number on this website: You can see the manufacture date, for White Labs it should be 6 months prior to the Best before date.
Viability: This is calculated by the website based on the manufactured date
Viable Cell count: This is calculated by the website based on the viability %

Your Starter Details
Flask Size: Enter the size or your erlenmeyer flask in litres. For a recent brew that had an OG of 1.069 I need to create a 1.7 litre start so that I could create a 100 billion cell harvest so I would recommend a 3 litre flask.
Gravity: 1.037 – 1.040 tends to be the standard for starters and so I leave this at 1.037. This is the SG of the starter brew you are going to make using water and dried malt extract.
Volume: This field is where you can play around with the size of starter you are going to make to achieve. So I start with 2 in this field and reduce it down until the data cell called Total Cells shown under the heading 1st Starter Step matches the Yeast cells needed data cell with the first section called Your Wort Details. Also if the Total Cells within the 1st Starter Step goes red you need to increase the number in this cell until it goes green.
DME needed: This is calculated by the website and tells you the weight in grams of Dried Malt Extract you require for the starter.

1st Starter Step
Method of Aeration: I would recommend a stir plate, to be honest they are fairy cheap to buy and also fairly cheap to make. I made one using a Celebrations tub and a computer fan, I had to buy a speed controller and some magnets but they are pretty cheap.
Starter Volume: This is copied from the previous cell within the section above.
Innoculation rate: This is calculated by the website.
New cells created: This is calculated by the website and shows the amount of cells that will be grown within your starter.
Total Cells: This is calculated by the website and will be the addition of the cells you are growing as well as the number of cells in the yeast packet or mason jar that you have been provided.

Starter with 100 billion cell harvest

Armed with that info we can now make our starter:

  1. I carefully measure the amount of water into a pan, I use filtered water just for extra piece of mind. Don’t be afraid of adding a little more water to account for boil off
  2. I start to bring that to the boil whilst weighing out the Dried Malt Extract (DME).
  3. When I start to see bubbles in the bottom of the pan I add the DME and stir vigorously until all the DME has dissolved, you want to get rid of all the lumps
  4. Now as it comes to the boil there is a very high risk of boil over so have a spray bottle of star san handy to spray on if it looks like it is going to boil over and keep stiring
  5. Once it is simmering then boil for 10 minutes
  6. At the end of the boil then chill down to yeast pitching temp. I use a washing up bowl in the sink, put a stainless dish in the bottom of the bowl and fill with water. I then add icepacks to the water. I let the saucepan sit in the bowl for a few minutes and I then carefully put the tap on so the water overflows out of the bowl. You can give the wort a stir with a sanitised spoon to aid cooling
  7. Whilst it is cooling I start sanitising my flask, stainless funnel, stir bar and some aluminium foil about A4 size is all you need. All that goes into the bottom of my sanitising bucket
  8. Once the wort is at pitching temp you can transfer that to the sanitised flask using the stainless funnel and also add the sanitised stir bar
  9. Then add your yeast
  10. Place the sanitised aluminium foil over the top of the flask and crunch it round tight
  11. Now place the flask on the stir plate and locate the stir bar just by moving the flask round until you hear it flick into place
  12. Start the stir plate rotating and adjust it until you have a small dimple formed on the top of the wort

I leave it on the stir plate for 36 hours, that seems about right for what I have found. After 36 hours I sanitise a mason jar that will hold 500ml comfortable, I think I have 1 litre mason jars. I then pour in the Amount to Harvest volume that is shown on the website towards the bottom of the page. Then I label the mason jar with the yeast type and date of harvest and set both the mason jar and the remaining starter in the flask into the fridge. I make sure I do this 24 hours before brew day but it can be a bit longer if you want just make sure the aluminium foil is scrunch tight on the flask.

Let me know what you think in the comments or any differences you do in your processes.

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