Creating a SEED CULTURE at 7,000' and 25% humidity

When I lived in Seattle, making a Seed Culture was simple and predictable using Reinhart's pineapple juice method.  

I now live in Santa Fe (7,000' elevation, though I don't know if that makes any difference to the project at hand), and it's very dry here, especially in winter.  Inside my home it rarely gets above 25% humidity, and honestly, I don't know if that matters either.

Anyway, after four days my Seed Culture has not one tiny bubble.  

Any suggestions?