Accidentally froze my starter (well partially)

[Queequeg]

See attached photos. I somehow hit the fridge temperature to max cold when making room for the starter. I would say about 40% is frozen.

There is also a thin layer of gray matter on top of the yeast cake, could that be dead yeast?

I had another stater in the fridge but luckily that was at the front so looks unaffected.

This was for an Imperial stout, so I am tempted to simply decant and top it up with another 2L fresh wort since a high yeast count is almost always favourable.

Input from anyone with similar experience
Would be great.

 

[Queequeg]

Here is a pic of the cake, not sure way my phone is rotating the pic

 

[urg8rb8]

Here is a pic of the cake, not sure way my phone is rotating the picView attachment 586377

I remember reading a while ago that freezing yeast kills off a big percentage of them. I think what I would do in your situation is the following:

Let it all thaw out, put it back into the fridge to cold crash it, decant it, then make another starter with whatever yeast is still alive.

 

[eadavis80]

I had a pack of 1010 where the smack pack itself got frozen because my brother misread my directions that said freeze the hops and put the yeast in the fridge. Figuring the yeast was dead I just bought a new pack. But, as an experiment, I thawed the frozen smack pack and made a starter just to see if it would ferment. Two days later the experimental starter's gravity was 1.010.

 

[Queequeg]

Ok, so I did some reading around the topic. It would appear the most significant factor on the yeast is the state it is in prior freezing and the duration of the freeze.

If the yeast is frozen during growth phases then the impact of the freezing is severe, don't expect to have many viable cells after that.

If however the yeasts are in starvation prior freezing then they are significantly more tolerant than they would be otherwise. I always let my starters ferment out then refrigerate to make the yeast hardy prior pitching to minimize osmotic stress.

Further reading indicates that you can expect between 5-65% loss in viability under these circumstances. Therefore I have made a new wort to refresh the decanted starter. 1.9L of 1.035 wort in fact. This should result in somewhere between 1.5mil/ml/P - 2.3mil/ml/P cells, depending on % loss of viability.