[punatic]

Which is a good Specific Gravity for a beer yeast starter

Right, that's what I was saying. 

Hey, the boards were a bit slow this morning, so I figured I'd stir it up a bit...   

[kgs]

If 10% of the volume of water is lost during the 10 minute boil (assume no solids are lost during the boil) ...

That calculation caught my eye. A ten minute boil is a long time for a small amount of liquid.  I brought a quart of water to a boil in a two-quart saucepan, uncovered the pan, and set the timer, then turned off the flame and poured out the water as soon as ten minutes were reached. The water had lost 50% of its volume.

Obviously, there are easy fixes: add preboiled water to restore the volume. Start with more than a quart of water. Cover the pan for part of the boil. Palmer recommends, "Put the lid on the pan for the last couple minutes" -- I do that anyway, to steam down any wort crystals and to kill the bugs -- and that would also help reduce loss. 

But the key is to know what your target OG should be for your starter and focus on that, and I can honestly say I haven't been doing that for starters (why, I don't know, since I am almost obsessive about hitting my OG for my beer).

Good thread!

[maxieboy]

Whew! I'm glad that's settled...

[denny]

That calculation caught my eye. A ten minute boil is a long time for a small amount of liquid.  I brought a quart of water to a boil in a two-quart saucepan, uncovered the pan, and set the timer, then turned off the flame and poured out the water as soon as ten minutes were reached. The water had lost 50% of its volume.

Very interesting.  I boil for 10 min. also.  I start with 9-10 cups and end up right around 2 qt.  some loss, but nowhere near 50%.

[punatic]

Is boiling the starter wort for sterilization or hot break, or neither/both/something else?

I used 10% cause it's easy and in the ballpark.

[kgs]

That calculation caught my eye. A ten minute boil is a long time for a small amount of liquid.  I brought a quart of water to a boil in a two-quart saucepan, uncovered the pan, and set the timer, then turned off the flame and poured out the water as soon as ten minutes were reached. The water had lost 50% of its volume.

Very interesting.  I boil for 10 min. also.  I start with 9-10 cups and end up right around 2 qt.  some loss, but nowhere near 50%.

I assume an uncovered pan, and a rolling boil, with the ten minutes starting at the beginning of the boil? I was surprised by my boil-off results myself, but there it was. I'll test it again for repeatability. As tests go, it's an easy one This time, I'll wear a lab coat.

I wonder if wort boils off more slowly than water. I wonder if I'm over-thinking this and should RDWHAHB (actually I am!).

[tygo]

I generally boil my starters in an Erlenmeyer flask which helps keep the boil off down.

I don't usually wear a lab coat though. 

[oscarvan]

[punatic]

Give him some chin whiskers and he looks a lot like Tom...

[bluesman]

Is boiling the starter wort for sterilization or hot break, or neither/both/something else?

I used 10% cause it's easy and in the ballpark.

Sterilization.

Boiling starter wort is necessary to produce a sterile environment for the yeast to grow in.

Hot break will come with the boil but I don't believe it's necessary.

[denny]

I assume an uncovered pan, and a rolling boil, with the ten minutes starting at the beginning of the boil? I was surprised by my boil-off results myself, but there it was. I'll test it again for repeatability. As tests go, it's an easy one This time, I'll wear a lab coat.

Ooohh, impressive!  A lab coat will definitely guarantee results!    I do my boil as you describe.  I use a 6 qt. SS post to boil a bit over 2 qt.  I wonder if the geometry has something to do with it?

I wonder if wort boils off more slowly than water.

I wouldn't think so.

[tschmidlin]

Give him some chin whiskers and he looks a lot like Tom...

You've got to lose the tie too

[beersk]

hmmm I usually do 1/2 cup DME to 1 quart of water.  I think sometimes I use just a little more water to account for boil off.  I don't typically worry about the gravity too much, as I believe 1/2 cup DME per quart of water gets me in the ball park with a 10 minute boil.  Cool the wort, shake, add yeast, shake some more.  I also intermittently shake my starter throughout fermentation also to keep the yeast suspended more. 
Seems to work fine for me.