Lager Issues: Gravity not changing

I feel like I already know what the answer is, but...

I'm trying my second lager right now, with the following details:
OG: 1050
Yeast: blend of White Labs 800 and 833
Temp: pitched at 44F, now at49F
Time so far: 48 hours

So the yeast is taken from my first lager batch, and it had a reasonably fast start and decent attenuation. For that fermentation, it was pitched at about 55F and allowed to rise to 60. I saved about 1 cup of slurry at the end (yeast, trub, cold break) and kept it in the fridge for 3 weeks while I accumulated enough dad points to brew again.

This time around, I measured my starting gravity at 1.050. After 24 hours, it was 1.048. After 48 hours, it's still 1.048. The sample seems bubblier, but quite clear. There's no convection going on, and it's covered in a layer of foam that I think has remained from when I shook to aerate at pitching time.

So, is my yeast dead, too cold, or doing its thing?

It's tough to tell sometimes with lagers since they're bottom fermenting. However, if you're gravity hasn't changed in 48 hours I'd say it's something else. Try warming it up to 55 or so, gently rock the carboy to rouse the yeast, and keep your fingers crossed.

You did not pitch enough yeast. So at that low of a temperature it is going to take a long time for it to get going. If you want to pitch lager that cold you need a ton of yeast.

belmontbrew said:

Time so far: 48 hours

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Am I reading this wrong or are you actually checking your gravity 48 hours after pitching? Give it some time to do it's thing... One thing to keep in mind is that more CO2 stays in solution (does not bubble) at lower temps so you are likely to see less airlock activity.

I still think your beer is probably fine especially since it has only been 48 hours but a few other things worth noting:

belmontbrew said:

I saved about 1 cup of slurry...and kept it in the fridge for 3 weeks

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After this long in the fridge your yeast will lose a significant amount of viability. (I guess 40%-50%). It would be suggested to either pitch more yeast, reduce your time in between brew sessions, or make a starter with your slurry to increase cell count/built the yeasts reserves. Doing this would decrease lag time and generally give you a better fermentation.

belmontbrew said:

... it's covered in a layer of foam that I think has remained from when I shook to aerate at pitching time.

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When making a lager shaking a carboy will not provide enough O2 for a proper fermentation. Having a more efficient manner of introducing O2 into the wort would also decrease lag time and help give you a better fermentation.

Thanks for the feedback! I'll definitely buy that the combination of not enough slurry plus a 50% drop in viability led to a major underpitch. Now, 72 hours later, gravity is starting to drop and the sample has some particulates in it.

And yes, since getting a refractometer, I usually check gravity every 24 hours from pitch until it stabilizes. Mainly because I'm curious and like to graph things.

belmontbrew said:

And yes, since getting a refractometer, I usually check gravity every 24 hours from pitch until it stabilizes. Mainly because I'm curious and like to graph things.

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I thought that refractometers only worked pre-fermentation and they do not work once alcohol is present....