You disagree with me. What else is new? I agree that the mention of expensive microscope was over the top, and I blame it on the whiskey, but if you are using older, undated bottles a microscope can come in handy. From fresh bottles, agree no microscope is necessary.
A microscope is completely unnecessary when culturing yeast. A microscope will not tell one anything that agar plates made simple and/or selective growth media will not bring to light. In fact, nine times out of ten, the reference culture can be separated from any contamination by observing colony morphology on an agar plate made with simple DME-base media. White fuzzy colonies are mold. Dark colonies are usually bacteria. Round, domed shaped, cream colored yeast cultures are usually domesticated yeast.
Here's a plate that I streaked with Scottish and Newcastle's Tyneside strain:
Here's a plate that I streaked with Southern Tier's yeast culture:
The S&N plate was streaked from a culture that I grew from a slant. The Southern Tier plate was streaked from a 40ml liquid culture that I inoculated directly from a bottle of Southern Tier Live (I start my cultures in media bottles). I transferred the well isolated colonies inside of the rectangle on the Southern Tier mini-plate to separate slants (that plate is only 60mm wide). Hopefully, people noticed the complete absence of fuzzy and dark colonies on both plates. The Southern Tier plate is proof that Southern Tier is not just winging biological quality control like many craft breweries. That plate tells me that Southern Tier's quality control program is overseen by someone who knows what they are doing. I have plated cultures from the two big yeast producers that were not that clean.