Tweaking fermenting timeframe due to elevation

I can only assume that elevation is having a decent effect on my fermenting. It took two full days before the air lock started bubbling. I talked to another homebrewer here in Mexico City and he warned me of the lag time. So, it sounds like that is common.

My question, should I extend my fermentation time? I am now at 14 days and there is no activity in the air lock. I guess I should take OG reading for 3 consecutive days and if it is stable, it is ready to bottle?

I can't imagine altitude having any effect on fermentation, I think maybe it's the amount of yeast and or the fermentation temp. I brew at 3310' above sea level, I've had batches blowing and going in 4-6 hours if I pitch enough yeast at the right temp. Altitude does affect boiling, my boiling point is only 203F so I tend to boil everything longer.

One possibility could be re-aeration potential of the air in your city. You might want to shake your wort more aggressively or get an oxygenation system. Or, you could always just plan for an extra week in primary and let it ride a little longer than us flat-landers.

Regardless, once your FG is stable for several days, it's done.

An airlock is a pressure release valve not a fermentation indicator. Buckets are infamous for having active fermentation with little or no airlock activity. Take an SG reading, wait 3 days and take another. Be sure to adjust both for temperature. If they are the same it is safe to bottle.

As far as altitude affecting fermentation I really don't think so. It's more likely other factors. Altitude will affect boiling temps and carbonation.

Im at 7500' above msl.

I used a Williams kit with the liquid WYeast. Started the yeast 3 days prior and it was nice and fat when I pitched it. Prolly could have aerated the wert in the fermenter better.

Plus side is, the temp has been steady 68* Should be perfect for the London Ale yeast which has a range of 62-72.

ill give it 3 wks in the fermenter.

Starting the yeast 3 days in advance might have something to due with the lag. The yeast likely activated, realized there was no food and went back into dormancy, but this time with their glycogen reserves depleted. Low glycogen mean low membrane permeability which means low activity.

I agree with woodland. Make the starter the day before you brew. The yeast should still be active when you pitch.

Altitude had nothing to do with it. People I know living at 7900' elevation have no issues with lag time. You most likely underpitched. What was the OG? A proper pitching rate typically requires making a starter, especially if the smack pack isn't super fresh. When you say you "started the yeast 3 days prior", did you make a starter, or just smack the smack pack? There are a couple of sites that can help you estimate how many viable cells are in your smack pack, and how many you need for an ideal pitching rate.

http://yeastcalc.com/

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