Yeast Starter

[Gytaryst]

I'm wondering if there is a factual method for calculating a 1.035 gravity yeast starter?

I've made a lot of starters and I'm not sure I've used the same method or mythical theory twice. The home brew academy states:

"1 gram of DME for every 10 ml wort (after boiling)."

I'm probably just missing something or reading it wrong, I'm sure.

Adding water to DME to get a total volume of 2 liters is a higher gravity than adding 2 liters of water to that same amount of DME. Maybe it's not a significant amount, (idk), or maybe it is. The fact is, it's not the same.

The pre-boiled volume is going to be more and the pre-boil gravity is going to be lower than the pitching volume and gravity. Again, maybe that's not a significant difference either??? But the fact is, there has to be a difference.

Most of the methods for making a starter aren't really too specific. Is it 100 grams of DME to 1 liter of water or 100 grams of DME and enough water to make 1 liter total? How long do you boil it and what is the average boil off? How much shrinkage is there in cooling and how does that affect the gravity and volume at pitching?

Or are all those factors so insignificant that it doesn't matter?

 

[chickypad]

I wouldn't over think it, for the purposes of a healthy starter something in the range of 1.030-1.040 is what you want so either way you should be in this range. If I'm calculating right with the second option you get about 1.037- i.e. put in the 100g DME then add water to get 1 liter total. At least that's what I do. I boil directly in the flask on my gas stove, just a minute or two so there is really no meaningful change in volume from boil off. I measure the liter cold, so shrinkage also wouldn't apply as you're chilling back to room temp.

 

[flars]

Try this calculator. I bring 1 liter of water to a boil and stir in 100 grams of DME off the heat. Boil off is minimal so I don't worry about it. The boil is to sanitize the kettle not the DME. DME only needs 171° for a minute for pasteurization.
http://www.brewunited.com/yeast_calculator.php

 

[Gytaryst]

I wouldn't over think it...

As soon as I asked the question that was my thought... "I'm probably WAY over thinking this - as usual."

for the purposes of a healthy starter something in the range of 1.030-1.040 is what you want so either way you should be in this range. If I'm calculating right with the second option you get about 1.037- i.e. put in the 100g DME then add water to get 1 liter total. At least that's what I do. I boil directly in the flask on my gas stove, just a minute or two so there is really no meaningful change in volume from boil off. I measure the liter cold, so shrinkage also wouldn't apply as you're chilling back to room temp.

Try this calculator. I bring 1 liter of water to a boil and stir in 100 grams of DME off the heat. Boil off is minimal so I don't worry about it. The boil is to sanitize the kettle not the DME. DME only needs 171° for a minute for pasteurization.
http://www.brewunited.com/yeast_calculator.php

Thanks guys. I think it's always irritated me that any instructions I found to make a starter always seemed blatantly vague. No one seemed to ever address the specifics I mentioned above, and without really thinking it through it just felt to me like there was some important information missing.

After writing it all out in the form of questions above - and after posting it, I realized the "specifics" I was stressing over were probably too insignificant to stress over.

 

[GPP33]

Actually the volume remains the same. The water is a solvent which means it dissolves the sugar which goes into the space between the water molecules. The volume will only change when you reach the solubility limit and the sugar no longer goes into solutions. 100g of DME into 1L of water is the same as adding enough water to 100g of DME to reach 1L. I boil for 5 minutes, after dumping the solution into the flask I boil up a little more and top off to reach my desired volume.

 

[IslandLizard]

I typically prepare 2 or 3, 1.6 liter starters at once, and always use a ratio of 100g or DME plus 1000 ml water, and get close to 1.038 each time. I add a little more water to a) compensate for evaporation during the 2 minute boil in a (large) 2.5 gallon pot, and b) to bring the gravity down by 1 point to 1.037. The refractometer is a handy tool to quickly check current gravity quickly.

Actually the volume remains the same. The water is a solvent which means it dissolves the sugar which goes into the space between the water molecules. The volume will only change when you reach the solubility limit and the sugar no longer goes into solutions. 100g of DME into 1L of water is the same as adding enough water to 100g of DME to reach 1L. I boil for 5 minutes, after dumping the solution into the flask I boil up a little more and top off to reach my desired volume.

This not accurate...
See the explanation by AJ.
And also here.