No fermentation

[Adam]

Last night I pitched a vial of WLP004 Irish Ale Yeast into 24litres of Stout with an OG of 1062.
The yeast was well within it's best before date and the wort was at 24degree C.
It's now over 15 hours later and there's no sign of fermentation yet. The ambient temperature in the room where it's sitting is a bit low, about 15deg C, but Iv got two other batches of beer happily fermenting alongside it, one with safale 05 and the other with a gervin yeast.
This is the first time Iv used liquid yeast so don't know if Iv done something wrong or should I just be patient.
At the minute I'm trying to raise the temp in the room to see if that helps.

[Simon_]

Did you make a starter? A vial of liquid yeast has a lower cell count than a sachet of dried yeast so there could be a longer lag time

[phoenix]

You generally need a starter with liquid yeast, especially if its come from the US and is a bit old. Heres a handy calculator which will help you work out how many cells are left in the vial and how many are required

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

[Adam]

Thanks guys. For some reason I had a notion that there was a higher cell count in liquid yeast and that fermentation would kick off faster. I'll make a starter next time around.

Is my best bet to just be patient now, leave it alone and wait for the lag phase to finish?
This brew is the first time I've deviated from a mash kit and made up my own recipe so I'm eager for it to go smoothly.

[Parky]

I've pitched a single vial into a batch of 20L myself not so many moons ago - took awhile to get up an running, but turned out fine in the end.

Best to be patient I think, but I would certainly try to get those temps up by a few degrees if you can. Looking at the spec. sheet for WLP004 it seems to be happiest at 18-20^oC. Safale US05 will work nicely from 15-22^oC, but the Irish Ale yeast seems to like things a little warmer.

Interesting article here re: over/under pitching yeast - http://sciencebrewer.com/2012/03/02/pitching-rate-experiment-part-deux-results/ Looking at the bar chart halfway down the page it would appear that under pitching produces more fruity esters. This might actually suit the character of a sweeter style stout, so may not be so bad if that's the profile of your recipe.

Also, just a thought - the ambient temp in the room may be a few degrees lower than that in the FV. Might be an idea to measure the temp in the FV so you can adjust the room temp. accordingly to keep things on track.

Hope it turns out well 

[Adam]

Cheers Parky, I have the room temperature up to 20degrees now and from reading that article you linked it looks like under pitching could have been a happy accident!

[DEMPSEY]

As has being said under pitching is an issue that many home brewers often do . In  this case you appear to have done so and so will likely  produce some off flavours as the yeast struggle to get  up to speed with all that lovely sugar . As it is a stout the esters will not be out of place as such but it will at least remind you of the next brew you do particularly if it is a pale ale or IPA as esters are not suited to these styles.  

[Adam]

It wasn't my only hiccup. Being the first time I was working from my own recipe, I now have a list of mistakes as long as my arm to remember for next time.
It was the first time I under pitched, first time I got a stuck sparge, first time I missed my target OG by a significant amount and the first time I forgot the whirlfloc tablet. Still though, the wort tasted excellent and I'm expecting a good result.

[imark]

From my experience WLP004 is a beast of a yeast. It'll happily ferment at 15C so don't panic. In fact best thing you could do now is stay away from it altogether as the most likely problem is you'll introduce unwanted guests.
Also have you ensured the fermenter is properly sealed. If it's not airtight co2 could be escaping there. I've assumed fermentation hadn't started previously as there was no activity from the airlock only to find I hadn't sealed the fermenter fully.

[Adam]

Yeah that was my first thought so I sealed all around the lid with wide tape, just to be sure. I'm pretty certain I have a good seal.