Does Fruit Lower the Viability of Yeast?

[WoodlandBrew]

Has anyone else seen the addition of fruit lower viability?

In all three of the most recent fruit beers I have made the viability of the yeast post fermentation was very low. In one case I measured the viability of the suspended yeast before adding the fruit and it was over 90%, but the harvested slurry was 1%! Even the density of viable cells was lower in the thick slurry than it was in the suspended yeast during fermentation.

Anyone have some ideas as to why this might be? Is there something I'm doing wrong?

Yeast was new in two of the three cases. I aerate the same way for all batches: Just pick the whole thing up and shake enough to make it sound like waves crashing on the beach for 40 seconds.

Here is how I prepare fruit:
http://woodlandbrew.blogspot.com/2012/11/fruit-easy-way.html

Here is how I count viability:
http://woodlandbrew.blogspot.com/2012/11/counting-yeast-cells-to-asses-viability.html

Beer                  Fruit         Yeast      Viability
Raspberry Cream       Raspberries   S-04       40%
Strawberry Champagne  Strawberries  EC-1118    1%
Sasion Terri          none          WLP-566    87%
50c                   none          WLP-566    85%
Raspberry Wheat       Raspberries   WLP-004    20%

 

[Golddiggie]

Maybe the acidity of the fruit is impacting the yeast.

 

[WoodlandBrew]

I've wondered that as well. It sounds like a good excuse to buy a pH meter! ... or at least pH paper that has a wider range than that used for mash tests.

 

[Golddiggie]

I've got the strips for both beer and wine use.