Author Topic: Yeast Starter Boiloff  (Read 366 times)

Offline kpfoley

  • BeerSmith New Brewer
  • *
  • Posts: 2
  • BeerSmith 2 Rocks!
Yeast Starter Boiloff
« on: January 04, 2020, 09:29:46 PM »
Say BeerSmith3 indicates that I need a 1 liter starter for my all-grain Porter recipe.  I put the required 3.38 ounces of dry malt extract into the indicated 1 liter of water, which shows that it is going to provide a 1 liter starter at a specific gravity of 1.036.  However, I know that I am going to lose about 150 ml due to boil off when I boil the starter for 20 minutes. 

My question is, does this mean that I then only have an 850 ml starter? 

Do I need to start out with more water, like 1.15 liters, so that I will end up with 1 liter after the boiloff?  Do I then have to add more than 3.38 ounces of DME because I am then using an extra 150 ml of water, more  than BeerSmith indicates?   

Or is the 1 liter starter shown as needed in BeerSmith the starting amount of water, and I don't have to worry about how much boils off?  Is the 1.036 specific gravity the value I have with my after-boil 850 ml, or is it 1.036 before I boil it, and then a different value after the 150 ml are boiled off? 

Or am I just overthinking this?  What is the correct interpretation?

Offline Oginme

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 2709
  • Goats, guitars, and a home brew; Life is good!
    • Longvu LaManchas
Re: Yeast Starter Boiloff
« Reply #1 on: January 05, 2020, 05:33:43 AM »
I can understand the confusion.  The volume of the starter in the program is the ending volume with the given amount of DME to give you the gravity target for the starter.  The real critical aspects of a starter are (1) the amount of sugar as determined by the DME, and (2) having a concentration of the sugar less than 1.040 in order to prevent the yeast cells from having to work too hard versus replicating themselves.  The actual volume is not critical as long as the (1) and (2) above are met.

I usually start by measuring out the amount of DME I want and then adding an overabundance of water to bring it to a boil.  After boiling for 10 minutes, I will check the gravity using a refractometer to make sure I am around the range of 1.034 to 1.038 gravity before removing the heat.
Recycle your grains, feed them to a goat!

Offline BOB357

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 494
  • Beer is my bucket list!
Re: Yeast Starter Boiloff
« Reply #2 on: January 05, 2020, 12:08:40 PM »
 Start with a liter of water and 100 grams of DME, simmer for 10 minutes in a flask covered with foil.

There's really no need for a rolling boil for 20 minutes. A 10 minute simmer will suffice. Covering with foil will causes a good part of the steam to condense and drop back into the flask. Between the minimal loss to boiloff and the volume added by the DME you'll end up very close to the 1 liter mark within the acceptable SG range for starter wort.