RotorHead6

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During my brew day yesterday I took two gallons of second runnings and saved to make starters with. I did this to save money on using DME all the time. I had a gravity reading of 1.020. I would like my gravity to be at 1.040 for starters. I froze the wort in .5 gallon batches.

My question is when it comes time for a starter, how much DME would I add to obtain a gravity of 1.040? I also thought about boil off to obtain a 1 quart starter but I also can't figure out what the gravity would increase to if I boiled off half of the liquid. Thanks for the help.

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Piotr

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Just go ahead and use 1.020 wort, yeasties will by even happier with thinner wort.

conpewter

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if you boil off half the water you'll end up with 1.040 wort.

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SpanishCastleAle

Recipes 

Figuring points is easy. Just remove the '1' from the gravity reading and use the digits to the right of the decimal as 'points'.

So 1.020 is 20 gravity points. If you are boiling it down or adding water to dilute it just divide or multiply the points by the ratio of the before/after volumes. So if you had 2 gallons of 1.020 wort and boiled it down to 1 gallon you'd have: 20 * 2/1 = 40 points. Your new gravity would be 1.040. If you aren't sure whether to multiply or divide by the ratio (or you get the ratio 'upside down') then just use a little common sense: Boiling it down will increase the gravity so your answer should show an increase in gravity. So in the example here...multiplying by 2 and then dividing by 1 will increase the gravity number. If you had mistakenly multiplied by 1 and divided by 2 then your answer would show a decrease in gravity which wouldn't make sense. It's really that simple.

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Ender

Recipes 

I agree, just use the 1.020 wort. It's a little low, but the yeast wont mind. To figure out the gravity numbers use this from Ray Daniels book:
Begining gravity * begining volume = Ending gravity * ending volume

so in your example:
20*2=X*40
so X=40/40 or 1 gallon

you can use this formula for anything any time. use it at the begining of your boil to find out what your ending gravity will be for a specific volume. Or use it for a known ending volume and ending gravity and find out how much beging wort you need or what the gravity should be.

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