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Brewed a 1.060 OG IPA last night (extract), pitched a packet of US-05 reconstituted with 5 ounces of water. Pitched at 68 degrees, but I wanted a clean fermentation with minimal esters, so I have the fermenter at an ambient temp of 63 degrees. Less than 12 hours of a lag, and I'm seeing some airlock activity, thermstrip on the fermenter reads 63 degrees. A couple of questions:

1.) I know this is the low, low end of US-05's preferred fermentation temperatures, but unfortunately, I do not have temp control at the moment, so its either 63 degrees (basement) or 68/70 degrees (main floor of house). Do I have yeast strain issues at 63 with US-05? I would warm it up to 68/70 after a week or so for a diacetyl rest (may not be necessary). The other problem is there might be some minimal draft/temp fluctuation in the basement this time of year.

2.) I have never top-cropped before, but want to use this yeast for a cream ale I'm doing next week. The common knowledge is that US-05 rarely needs a starter, but since I am propogating from a working batch, I thought it might be a good idea. The alternative is just cropping, funnel into a vial, and pitch into the cream ale (OG will likely be low .060's). Small starter with the stir plate or no?

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up vote 1 down vote accepted

The only problem with a complete repitch is that you generally want to go from lower gravity to higher gravity, lower IBUs to higher IBUS, lighter to darker.

Top-cropping should work fine, but you'll need to harvest while it's a high-kraeuesen (if you had activity this morning, you'll be at high kraeusen this evening or tomorrow morning), and that can be a smallish window: generally 2 or 3 days max. At the temperature you're fermenting at, it may take a little longer and have a little less "high" kraeusen than otherwise, but it should be fine. the only reason the dry yeast doesn't need a starter is that you're pitching so many yeast cells from a 11.5g packet. You will most likely need a starter unless you can get the whole kraeusen directly into the next beer while it's still fresh.

It should be fine at that low temperature, as long as the temperature is stable there. Basically, if it's fermenting at that temperature now, it will be fine there for the duration. If you're really concerned about diacetyl, you can certainly move the fermentor to the warmer area of the house when the yeast has had 4 or 5 days of fermentation (or has 2-5 gravity points remaining to hit your FG).

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stupid follow up question, but when the yeast is krausening, the cells are actually metabolizing the sugars right? If I'm removing a few hundred billion cells from the fermentation, why doesn't that stress the remaining yeast, particularly if they have finished multiplying? Or is the krausening stage when multiplication is at its highest? –  Pietro Feb 2 '12 at 13:45
    
I don't know for certain, but I think that the cells in the kraeusen aren't actually doing much beer processing, because they're floating on top, rather than churning around in the wort. Also, there are a lot more cells in suspension working on eating the sugars than there are floating on top, so harvesting kraeusen shouldn't have a significant effect on your attenuation. –  baka Feb 2 '12 at 18:02
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I've used rehydrated US-05 for my last 4 batches. The typical room ambient is ~61-63 degrees. I typically pitch when my fermometer reads are 63-65, and the yeast take off within 6-8 hours. For the active portion of fermentation, the fermometer typically reads between 67-69.

Being that this yeast is spec'd on the low end at 59 you should be okay. You could try rousing them periodically by gently rocking the carboy..

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