Good luck with your porter! I handle this problem by stepping up a vial into multiple 1L starters, and then I save one for future use. Other's certainly do it differently, but I find this method works the best for me and is quite simple.
1. Determine the predicted OG for your first beer.
2. Visit
Mr. Malty to determine how large a starter you need for this beer. If you don't have a stir plate (you're in good company if you don't), plan to intermitently shake the starter.
3.
Create a 1L starter using 1/2c DME to 2c water. I like to make my starters in sanitized juice bottles. This has a few advantages - first, they're disposable. Second, you can tighten the cap to shake the starter really well. Third, you have way more headspace. I've done starters in mason jars with foil, and it's a pain. They almost always blow off, and shaking is a chore. With juice bottles, I tighten the cap, shake once, burp, and repeat. When it's all said and done, I throw the bottle away.
4. At this point, you have a 1L starter fermenting on your counter. Make sure you continue to intermitently shake, and give it enough time to fully attenuate. I find this takes about 2 days. There certainly isn't any rush.
5. With the 1L starter complete, put it in the fridge for a day and then decant.
6. Now, make enough wort for as many 1L starters as you need
+1. If you need two litres of starter for your porter, make three litres. Use the same rate of DME to water as above.
7. Split the 1L starter you made between the containers you're using to make your starter.
8. Once the yeast has reached room temp, and the wort has cooled to room temp, split the wort evenly onto the yeast.
9. Intermitently shake these starters until they've reached full attenuation, chill in the fridge, and then decant all of them.
10. Combine all the yeast from the starters
save one into a single container (I use mason jars). Pour sterile water (bottled water or boiled tap water) on top to
almost fill the container and cover with foil. This will be the starter for your porter. You can save this in your fridge until the day you brew. Be sure to remove this starter from the fridge and let it warm to room temp before you pitch into cool wort.
11. Place the yeast from the remaining 1L starter into its own container (another jar), fill with sterile water, and cover with foil. You can use this starter to create all future yeast for your brews.
12. Repeat the process from step 6 onward using this 1L starter for each new batch of beer. Don't make complete starters for your current and future batches at once if they're spaced by a few weeks - you want to make sure the yeast you pitch is fully viable.
And that's it. 12 steps may seem like a lot, but it's a very simple process - the yeast is doing most of the work. Good luck!
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