How did my yeast die?

[skibb]

So I made a 3000ml starter and let it work its magic for 3 days. After that I put it in the fridge to cool it down so that I could decant it, which I did. Come brew day I ended up not being able to get all the ingredients I needed. So I stored the yeast starter in my fermentation chest freezer (It was set at 40 degrees) until a week later when I brewed my batch. I cooled the batch down to 62 degrees and allowed the yeast starter to raise to that temperature as well before pitching. It is now 4 days later and still no signs of activity...how did my yeast die? I covered the yeast container (a glass gallon jug) with aluminum foil during storage.

 

[weirdboy]

If they froze in solution the cell walls will explode and kill them.

 

[COLObrewer]

Your procedure looks sound, (unless the temp did dip to freezing) what yeast is it and what temp is it now?

 

[Revvy]

What are you defining as "no activity?" How do you know your yeast is dead? Have you taken a hydro reading? That's the only way to tell what your yeast is doing.

 

[ksbrain]

Assuming "no activity" means no foam, no ring of gunk, etc. I'm thinking the 40 degree freezer actually sometimes hit freezing temperatures. If your water bath where your temperature probe sits has a larger volume than your yeast did, the yeast would get colder than the bath. Though that's a lot of colder.

 

[Wolfy]

If you put the starter on the base of the freezer, its possible that the yeast actually froze even if all the liquid in the starter did not.
As others have said, take a gravity reading to ensure there has been no activity before you assume the yeast is dead, if you're still at the same OG you'll need to pitch new yeast.

 

[skibb]

It was hefe yeast. The wort with the yeast in it is currently sitting at 62 degrees. It was sitting at the bottom of the freezer so its sounds like to me they probably froze and exploded. What a horrible death. I will take a gravity reading today just to make sure (even though I don't/haven't yet seen bubbles).