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Old 12-05-2012, 09:14 PM   #1
jcaddy35
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Default Yeast Starter- calculating the amount of DME

When calculating the amount of DME to use in the yeast starter, should I be using the beginning (pre-evaporation) amount of water, or the ending (post evaporation) amount?

For example:

If I want a 1 Liter yeast starter that has a gravity of 1.037, I would need to use 1.5 Liters in the pot to boil for 10-15 minutes. Therefore, I would need either 5.2 ounces of DME (which gives me 1.037 in 1.5 liters), or 3.5 ounces of DME (which gives me 1.036 in 1 liter). Which one is correct?

I'm guessing it's 3.5 ounces since the water evaporates, but not the DME. Am I correct here?


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Old 12-05-2012, 09:21 PM   #2
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Pre...it makes life easy as starters aren't exacting so it doesn't much matter if you are off by 5 points. I use 1 gram DME/ 10ml water, add the DME and yeast nutrient into my flask, top up to desired level and boil.


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Old 12-05-2012, 09:23 PM   #3
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Quote:
Originally Posted by jcaddy35 View Post
When calculating the amount of DME to use in the yeast starter, should I be using the beginning (pre-evaporation) amount of water, or the ending (post evaporation) amount?

For example:

If I want a 1 Liter yeast starter that has a gravity of 1.037, I would need to use 1.5 Liters in the pot to boil for 10-15 minutes. Therefore, I would need either 5.2 ounces of DME (which gives me 1.037 in 1.5 liters), or 3.5 ounces of DME (which gives me 1.036 in 1 liter). Which one is correct?

I'm guessing it's 3.5 ounces since the water evaporates, but not the DME. Am I correct here?

You are correct. Post boil is used to calculate gravity. Although you shouldn't have much boil off at all making a starter. You just need to get it to a boil and then cool.
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Old 12-05-2012, 09:23 PM   #4
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I always put the recommended starter amount in the actual beaker. So if it calls for 1 liters of starter and 1/2 cup DME, I make sure that volume is what's in my beaker in the end, not 750 ml after boiling evaporation. I don't think a couple points off your target starter OG will really matter, especially if you're only pitching a slurry and not the whole volume.
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