CONTAMINATION

I’ve often been told, “my sourdough's dead”. Sorry folks, it’s virtually impossible to kill it off. You can keep it almost indefinitely at room temperature, in the fridge or even freeze it. It’s still alive and well, simply dormant. If kept at room temperature it’s at its most vulnerable, so you have keep an eye on it to make sure it doesn’t start to grow mould. If it does, scrape off the mould and refresh. How many times? Until you get to the consistency you want and the acidic smell is bearable. Say 3 times. If it’s been kept in the fridge or freezer all you need do is allow it to return to room temperature and refresh it a few times, as above.

However, contamination is another matter. My sourdough loaves went tasteless about a month ago, no tangy aftertaste at all. The loaves, whether baked after being in the proofer, or retarder overnight, certainly rose. But the taste was zero. I realised that “mother” (or the leaven if you prefer) had been contaminated with commercial yeast. There are several possibilities of how this happened and I’ll come back to that in a moment. Curiously, Chris R contacted me and reported the same problem. Not surprising as I’d recently given him some leaven.

Fortunately I had a very dormant pot of “mother” sitting in the fridge, untouched for more than 3 months. It smelled pretty high and some water had separated from the flour. Back in July I’d been given some stone-ground flours, by the miller at Foster’s Mill, and wanted to try them out. I’d converted some of my existing, and at that time untainted leaven, by taking a portion of it and refreshing it 3 or 4 times with the Foster’s Mill flours and by doing so diluting my existing leaven to a minimum in the refreshed leaven. I then made some very tasty loaves using the Foster’s Mill flours and leaven. Holiday time came so I stored the remaining Foster’s Mill leaven in the fridge. Luck was on my side as the stored Foster’s Mill leaven was uncontaminated.

Here are a few tips to keep commercial yeast from contaminating your precious leavens:
o Never use a utensil to mix a sourdough leaven after it has come in contact with commercial yeast
o Never remove excess leaven from a mix that also contains commercial yeast and put it back in the leaven container
o Never take excess water out of container that contains yeast and put it aside for future use

If your leaven(s) are in perfect condition I suggest you store a portion of each in the freezer. Should any of your leavens in regular use get contaminated you’ll have a backup supply. A word to the wise is sufficient.


Carl
2 December 2009