[stufr67]

I am seeing conflicting guidance on how small a micron I need to use to remove all the yeast.  Anyone know which, .2, .5 or 1?  I would like to use the biggest possible and get the job done.
I am doing a cider that I want to back sweeten and force carbonate.  My wife is sensitive to sulfates and I don't want to add much to this if I don't have to.

[crakers540]

Yeast vary in sizes, from 2 to 40 um.  S. cerevisiae (most common in brewing) are around 5 to 10 um.  The problem with filtering ALL the yeast out may come with the "bud" size, which is usually around 1 um. 

I would recommend a step filtration starting out with larger pore sizes to remove the larger particles, and work your way down to 0.45um, being careful not to introduce oxygen while going through the steps.  The filters will need lots of surface area so they do not become clogged to quickly. 

Lots of info on filtering on the internet.

[Hand of Dom]

Could you not pasteurize it, and then force carbonate?  It might be simpler than running through multiple filters.