Lag time - explain it to me, please

[Judochop]

First of all, when does the clock start on ‘lagtime’?

1. Is it the time between pitching and visible fermentation?
2. Or, is it the time between the moment the wort is cooled and visible fermentation? (eg. If I cool my wort, transfer it to the fermenter and move it to a fridge to bring it down to 50 degrees over a period of 6 hours and then pitch a lager yeast, is that all considered lag time?)

Second, why is it a concern?

Presuming definition #1 is correct, what is happening at the specific time between pitching and visible fermentation that should make us concerned? If the yeast takes 50, 60, 70 hours to start a krausen… so what?

If the answer is simply ‘risk of contamination’, then is not that also a concern from the point that the boil stops and the wort begins to cool? (See definition #2 above.)

Or, is there actually a GREATER risk of contamination in that period between pitching and active fermentation?

Or, does a long lag time indicate that the yeast is struggling through a process which in turn may lead to undesireable flavors?

I am confused. Please help.

 

[JonK331]

Answer #1 is correct. Lag time is the time between pitching and the start of visual fermentation. This is the aerobic phase of fermentation where the yeast are consuming oxygen and reproducing. Yeast consume the oxygen first, when it runs out, they stop reproducing and start consuming the sugars.

The biggest concern for contamination is when the wort drops below 170f before fermentation begins. Long lag times are generally associated with underpitching and/or not enough oxygen in the wort. If you are worried about contamination while you cool your lager down to pitching temp, I wouldn't, it's really not that big of a concern if your sanitation practices are good and you keep the fermenter closed.

 

[kanzimonson]

Good answer JonK. To add to it, nobody should ever think "long lag = bad, short lag = good." You want to have some sort of lag time. When yeast are growing, they are producing most of the flavor compounds we associate with beer. If you have a short lag time, you will have less flavor overall.

As an example, in my early homebrewing days before I fully understood how to properly use yeast, I once pitched an entire yeast cake onto a beer instead of pitching the proper amounts. By my calculations, I estimate that I probably pitched 5x the proper amount. The yeast strain was Wyeast 1762, the Rochefort strain. This strain is notorious for producing delicious banana, tropical esters and light spicy phenols. But because I overpitched, I got NONE of that. It was a very boring and bland beer.

When I pitch the right amount of yeast (using Mr Malty), my lag is almost always 12-18 hours. This is regardless of the state of the yeast - from the pack, fresh starter, reharvested slurry - it doesn't matter. If I pitch .75mm cells per mL per *Plato, I usually see activity in 12-18 hours (for ales).

 

[JonK331]

Good answer JonK. To add to it, nobody should ever think "long lag = bad, short lag = good." You want to have some sort of lag time. When yeast are growing, they are producing most of the flavor compounds we associate with beer. If you have a short lag time, you will have less flavor overall.

As an example, in my early homebrewing days before I fully understood how to properly use yeast, I once pitched an entire yeast cake onto a beer instead of pitching the proper amounts. By my calculations, I estimate that I probably pitched 5x the proper amount. The yeast strain was Wyeast 1762, the Rochefort strain. This strain is notorious for producing delicious banana, tropical esters and light spicy phenols. But because I overpitched, I got NONE of that. It was a very boring and bland beer.

When I pitch the right amount of yeast (using Mr Malty), my lag is almost always 12-18 hours. This is regardless of the state of the yeast - from the pack, fresh starter, reharvested slurry - it doesn't matter. If I pitch .75mm cells per mL per *Plato, I usually see activity in 12-18 hours (for ales).

I agree but it depends on how you define "long" and "short." A lag time of more than 36 hours usually is not ideal. I like to pitch lots of yeast into a well oxygenated wort. The aerobic phase is very important, I have made batches where I oxygenated longer than necessary and the lag time ended up being a little longer, this just means there was more O2 present and the phase lasted longer. The effect was a very vigorous and relatively short fermentation period.

 

[Judochop]

Long lag times are generally associated with underpitching and/or not enough oxygen in the wort.

You say 'generally associated'. Taking you literally, that means that I could potentially experience a long lag time (36 hrs or more) even after pitching the right amount of healthy yeast into a well oxygenated wort?

Can't say I have. But I could?

Bottom line is that a long lag time isn't a problem in of itself, though it may be a sign of something that is a problem (ie. under-pitching and/or under-oxygenating).

Do what's right by your yeast (count, O2 and temp) and don't sweat the lag time. Check. :rockin:

Contamination not an issue if sanitation is up to par. Check. :rockin:

 

[JonK331]

You say 'generally associated'. Taking you literally, that means that I could potentially experience a long lag time (36 hrs or more) even after pitching the right amount of healthy yeast into a well oxygenated wort?

Can't say I have. But I could?

Bottom line is that a long lag time isn't a problem in of itself, though it may be a sign of something that is a problem (ie. under-pitching and/or under-oxygenating).

Do what's right by your yeast (count, O2 and temp) and don't sweat the lag time. Check. :rockin:

Contamination not an issue if sanitation is up to par. Check. :rockin:

Yup, usually when you do everything right you will not have a long lag time though.

 

[Judochop]

Yup, usually when you do everything right you will not have a long lag time though.

Hypothetically though, if you did do everything right and you still see a long lag, I guess y'gotta figure it was a bum packet/vial of yeast to start with then? Where else would you look to find an explanation? (Aside from silly things, like missing the fermenter when you pitch and pouring the yeast down the backside of the carboy, etc...)

 

[kanzimonson]

I have never once suspected I got a "bum packet of yeast" like I see people on HBT saying. In disclosure, I've never had yeast shipped to me so that's in my favor.

If you use Mr Malty to estimate viability, and then make a starter based on the number of cells you have, then you won't have a problem. And I would always make a starter with old packets. Even if I had the right number of yeast for my batch, but it was in 8 packets with 20% viability, I would still make a starter (with fewer packs) to get them active.

 

[Judochop]

I have never once suspected I got a "bum packet of yeast" like I see people on HBT saying. In disclosure, I've never had yeast shipped to me so that's in my favor.

I have "suspected", but just once. And that was one shipped to me, over the course of a 95+ degree Chicago heat wave. It arrived rubber banded between two thoroughly melted ice packs.

However, back then my cleaning and sanitation practices weren't the best, and I fermented that hefeweizen in my apartment during that same chicago heat wave, probably close to 80 degrees.

So... let's just be fair and say 'never'.