First time yeast starter question

So when Mr. Malty recommends a certain size yeast starter, is that assuming a constant OG of 1.040 for the starter? i.e. If I make a 1L starter at 1.040 and realize I need 2L, then more fermentables need to be added along with top off water when it gets diluted? Or will they multiply enough to get the right cell count

Yes - if you double the starter size, you double the fermentables.

First take a look at the Brewers Friend yeast starter calculator. This calculator presents the numbers in an easier to understand format. Check the information below the calculator for the explanation of the pitch rate to choose in the calculator.

http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

Not all starters are made with a 1.040 wort. Old yeast should be started with less fermentables. Often this is 1.020. It can be less.

For the situation you posted you could double the fermentables or make a two step starter. For a two step starter the 1 liter starter would be fermented out and then the step up starter would be made. Plug your numbers into BFs' calculator and you will see how each step will progress with yeast cell count estimations.

BFs' calculator will also tell you if your starter volume will achieve the desired number of cells you need.

I will usually decant the spent wort between steps if steps one and two will equal 3 liters or more in volume. It is just easier to cold crash less than three liters in the refrigerator to get ready for pitching.

Thanks! That's a much better tool than mr. malty

An easy rule of thumb for a starter is 10:1. Use 1 liter (1000 ml) of water and add 1/10 that amount of DME, 100 grams. This also makes it easier to step up to a larger starter.