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I boiled and pitched a low-gravity (~1.033) Scottish Ale this past Sunday.

The wort was cooled via immersion to under 75° F and then aerated via a whisk-on-drill contraption before pitching the yeast. The house has stayed at a consistent 75° F the whole time, within range of the yeast's comfort zone.

As of this morning (Wednesday), there was no activity to speak of. Despite verifying the airlock and seals were all tight, it was apparent no pressure had been generated. I removed the airlock and found neither krausen or any yeasty smell--it looked and smelled the same as before I lidded it on Sunday.

When I came home this afternoon, I was about to attempt a re-pitch when I found something rather different. The airlock was bubbling away. I popped the top I found quite a healthy-looking (if a bit dark) krausen, and a definite yeasty smell. Perhaps it wasn't quite the smell I expected (I'm not used to smelling it mid-fermentation), but it certainly smelled more of beer than of wort.

So what was going on the past three days that made the yeast take so long to kick in? Do I need to worry about acquiring an infection during this time without alcohol, and particularly having now opened the lid twice (I'd never opened it before bottling time in the past)? Or should I just relax, not worry, and drink a homebrew?

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What strain of yeast was it? –  mdma Aug 15 '12 at 22:50
    
Wyeast Scottish Ale 1728 smack pack (see link in post) –  Ray Aug 15 '12 at 23:16
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2 Answers 2

up vote 3 down vote accepted

I've had 72hr starts also with some yeast strains, particularly the Irish Ale strain from white labs, WLP004 either pitched directly from the vial or built up from a 10ml slant in a starter.

This is usually a sign of underpitching, and the yeast require many more generations to build up sufficient numbers of cells.

I wouldn't worry about infection, the yeast will also acidify the wort to some degree, which helps prevent any airbourne contaminants from taking hold. Also, you opened the fermentor not long before visible fermentation started, so there wasn't much time for any other organisms to take hold.

I'd relax, your beer will be fine. Attenuation may suffer a little with such a long start, but that's not so bad in a scottish ale.

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+1 and thanks for the reassurance. I'd chatted with LHBS owner about it earlier this afternoon (prior to getting home and finding activity), and he insisted I must have pitched while it was too hot or failed to aerate or something. Good to know this happens. –  Ray Aug 15 '12 at 23:20
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I realize this was answered already, but in case you didn't know... Despite the fact that Wyeast and White Labs say their vials & smack packs are enough yeast for a 5 gallon batch, Jamil Zainasheff/mrmalty.com recommends pitching 2 smack packs for a 5 gallons or making a starter. This yeast pitching rate calculator will tell you how much to pitch:

http://www.mrmalty.com/calc/calc.html

For a 5 gal batch you're generally going to need 2 vials/smack packs or a ~1.5 liter simple starter.

You can make a smaller starter (1 liter) if you build a stir plate. I built one last week for about $25 and it worked like a charm. They can be built for even less if you have an old PC you can harvest the fan and hard drive magnet from. You can google for DIY homebrew stir plates to find lots of different plans.

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My smack pack was manufactured in June. According to the calculation on Mr. Malty, that leaves around 50% viable. So if it was a fresh pack, the site thinks the one would be enough for my low-gravity beer, but it was just old enough that they say it should be two. I think this essentially agrees with mdma's answer--I likely underpitched. I guess I should just make starters from here on out. –  Ray Aug 16 '12 at 10:32
    
I wouldn't think a 1.033 beer really needs a starter. –  Graham Aug 16 '12 at 12:31
    
It doesn't need it, one smack pack/vial is enough according to the manufacturer, but it might make it start faster. –  paul Aug 16 '12 at 14:57
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The purpose of making a starter is not shorter lag time, it's for better fermentation and better beer. Although I agree that for beers under 1.040 you don't generally need a starter, given a fresh pack of yeast. –  Denny Conn Aug 16 '12 at 15:19
    
Agreed, that's not the purpose and it's probably not necessary. I've had good experiences adding yeast vials directly to 5 gallon batches in general. But I usually make a starter with liquid yeast anyway, since it doesn't hurt and it gives me a chance to break out the Erlenmeyer flask! –  paul Aug 17 '12 at 19:51
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