Well to be honest I'm not going to get too worried about this 'wildcard waiting to happen'.
Are you saying that yeast can somehow magically escape from enclosed tanks (where cider is fermented) and then float towards the yorkshire squares and contaminate the fermenting beer. I'm no biologist/brewer but that seems a bit far fetched to me.
Risk of contamination in such as filtration is presumably avoided by, as you say, proper cleaning regimes.
Yeast is just like any bacteria and given even the slightest amount of exposure cells will go airborne. The cider fermenters are sealed during fermentation but they have to pitched which means live yeast will be exposed for a fair amount of time, so no magic needed. There's also the risk of cross contamination in the yeast store but presumably that'll be kept well away from the beer and lager yeasts.
Anything's possible but not necessarily likely. People say all sorts of stuff against SS but one thing that is never criticised is the quality of the beer. In that sense I think it's in safe hands and there's no need to worry
The quality of the beer is usually excellent. However, if you read some of the posts on this forum then you will see that it is not always perfect.
I usually only drink real ale, but the quality of the Old Brewery Bitter in my local Samuel Smith's has not been great of late. Instead, Ive been drinking mix on the recommendation of a former bar tender.
I started this particular post as a result of trying the Samuel Smith's cider for the first time on a hot day the other week and really liking it - it's the best fizzy cider I've had in years and is now my drink of choice at my local Samuel Smith's pub.
DB.