My most recent attempt at propagating a yeast starter has proved disastrous. I had hoped to produce a large cell mass and use my nerdy beer equipment to do a cell count and pitch a known number of cells per mililitre of wort, but this plan came to an abrupt end when I removed the foil from the flask to take a sample for counting and was met with the unmistakable smell of contamination. In case you don't know, this smell is identical to the phenolic fluid that the local council use to wash out lanes and such that have been used as a communal urinal by non community minded individuals. If you have been spared the unpleasant experience of passing a lane that has been washed out thusly, the classic association with this smell is hospitals in the old days when everything was scrubbed with phenol and super bugs gave them a wide birth.
I was miffed with this turn of events because I have never suffered a spoiled yeast starter before, but know exactly where the contamination crept in. My usual method of aeration is to vigorously shake the flask of wort in much the same way I strenuously shake the 25 litre carboy of wort before fermentation kicks off. This time, however, I took the advice of an American website which suggested shaking smaller volumes in a separate vessel and pouring into the primary flask. I was keen to get as much oxygen into the wort as possible, but was all too aware that this method required the wort contacting far more surfaces and atmosphere than I like. I'll be sticking to the tried and tested next time.
The pictures with this post are microscope shots of the contaminated starter. I must admit to being a little confused by it all because my experience with yeast morphology is limited. What we are looking at is either the smaller desired yeast strain along with a typically larger wild yeast strain that caused the nasty smell, or we are looking at the larger desired yeast strain accompanied with smaller bacterial cells. I'm not certain, but there's definitely something in there that shouldn't be.