Feeding yeast starters

So I am going to do a yeast starter for an AB clone tonight that I want to brew next week. I have heard people talking about feeding your starters to continue to grow more yeast for bigger beers or more beer. I am going to be brewing a 7.5 gallon batch using wlp007. I was thinking off starting off with about a 500ml starter and then feeding it maybe Monday or Sunday night. i have read that you want to cold crash the starter after a few days in then dump off some of the excess wort and then dump more fresh wort in to give more sugars. I have also read that you can (if you have a big enough container for your starter) dump more fresh wort on top of the old.
Any thoughts on this? Also, I would just continue to stir plate away the whole time correct?

Thanks!

It depends on what the OG of the wort will be. 500 ml is probably too small of a step. I generally do only 1 step starters of about 1L with a stir plate the night before for a 5 gal batch and just pitch the whole thing. Most of the growth occurs within 12 to 18 hours of pitching the yeast into a starter.

Mrmalty.com

According to the Mr Malty calculator, 7.5 gal of 1.048 wort requires a starter of 1.27 L with a stir plate.

So it says I need 2 vials and a 1.17L starter for 7.5g batch at OG of 1.070. Do I really need 2 vials or can I feed the yeast to make it work for a 7.5g batch at 1.070 OG?

Matteo57 said:

So it says I need 2 vials and a 1.17L starter for 7.5g batch at OG of 1.070. Do I really need 2 vials or can I feed the yeast to make it work for a 7.5g batch at 1.070 OG?

Click to expand...

If you slide the Growth Factor to the right, the calculation will give you 1 packet at 2.91L with a stir plate. For doing a multi step, I don't know what you would use exactly, but if you use these 2 sites, you should be able to calculate what you need.

Mrmalty.com

Wyeast Laboratories : Home Enthusiasts : Brewers : Pitch Rate Calculator

According to the 1st site, you need approx. 383 bil cells, or 13.5 mil/ml. Just playing around with the Wyeast, I get 2 stages of 1L (0.26 gal) with a stir plate to achieve your desired pitch rate. You can play around with the numbers to see what you get.

Matteo57 said:

So it says I need 2 vials and a 1.17L starter for 7.5g batch at OG of 1.070. Do I really need 2 vials or can I feed the yeast to make it work for a 7.5g batch at 1.070 OG?

Click to expand...

I get different figures than you. For a 1.070 brew at 7.5 gal., you need 362 billion cells of yeast. You can obtain this by a number of ways; 2 packs of 11 gm. dry, 4 packs of liquid yeast (harvest/production date must be today), or 2 packs of liquid (harvest/production date today) in a 3.13 liter starter, or 177 mL of yeast slurry (harvest date is today). Notice that the harvest date is important. If your liquid yeast samples whether from Wyeast or White Labs or from washed yeast happens to be aged somewhat will change the amount needed to obtain that 362 billion cell number. So it's good to have fresh yeast. If it isn't, plan on using more. Dry yeast will stay the same.

I am not familiar with stepping up a starter. I either use dry yeast or use multiple washed yeast slurry samples in usually a 1500 mL. starter. This is why I like to always make 8 pint jars of washed yeast from generally every beer I make. I'm cheap I guess.

Hope this helps.

Everything you said is correct. You can either step up the starter, cold crash, decant and then add fresh wort or you can keep adding in a big enough vessel. Stepping up the starter accomplishes essentially the same thing as using multiple vials for a single step starter, namely creating heathier robust yeast cells instead of a multitude of weak ones. If your beginning at 500 ml with an OG of about 1050 and then stepping it up every couple of days with a 300-500 ml addition you should be good with one vial.