The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Contaminated Starter?

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ANFlynn's picture

Contaminated Starter?

I was wondering if it is possible for your sourdough started to some how get contaminated with commercial yeast?  My started (made by Reinhart's method in BBA) made great bread for a while.  Lately, though, I have noticed that the rise is too fast and although the starter still smells sour, the bread isn't coming out like it used to.  It acts just like instant yeast!  Thoughts?

LindyD's picture

I guess if you leave your sourdough culture in an uncovered container and spoon commercial yeast next or it or above it, some yeast to could fall into the container - but the presence of such a tiny amount of commercial yeast would soon be eliminated through the regular refreshments of the culture.

How many hours does it take your culture to double now, versus before?  Has the temperature of the refreshment water changed, or the room temp?  How about hydration?

ANFlynn's picture

I keep it at 100% hydration, and usually triple it to feed it.  It doubles within 3 hours, and when I make bread, the dough can double in 2-3 hours!  I can't really imagine that any contamination with commercial yeast could have done that, since the low pH of the starter should kill it anyway.  There was a time, however, around Christmas when the starter sat in the refridgerator for 6 weeks without getting refreshed.  I rebuilt it, and it is since then that this problem has arrisen. 

I think I will just build a new one and starter over. ;)

LindyD's picture

Don't know if you use warm water, but you could just use very cold water when refreshing it, and place it in a cooler room.  You could also try lowering the hydration.

I maintain a very firm starter - about 60% - and can manipulate the timing by water and room temp.  If I'm planning to bake the next morning, I'll feed it around 11:30 p.m. using my very cold well water, then move it a cool room.  By morning, it has a nice dome and is ready to go.

Warmer water and a warmer room will get it to double within five or six hours.

Sounds as if you have a starter on yeast steroids!

alarisch's picture

I made a starter using the same method. Ive had the starter for about a year. Last Oct, i got too busy with work, and kind of forgot about it, and didnt feed it for like 2 months. In Feb I started a week long refreshment period, and since then i have the same problems. The starter will defiantly double in size with in 2.5 hours. I feed it at a 100% hydration. Im not sure if its just a really healthy starter, or something is wrong with it. But ive also noticed that it doesn't really have a sour smell to it any more. Smells kind of like a very mild yogurt, but quite musty. If anyone has any suggestions, please help. 



ANFlynn's picture

I am thinking that I will try converting my 100% starter to a firm 60%, with cold water and really try to promote a slow rise.  The whole "starter on steroids" thing isn't making for good bread!

Not that any of this is a big deal, its really not too tough to just start over, but I am curious about the science.  I don't really believe that our starters are contaminated with commercial yeast even though they act like commercial yeast.  I think that even if you tried to make a starter with commercial yeast, eventually it would get "infected" with natural yeast which would take over.  I suspect what is going on with our starters has more to do with the bacterial types that have colonized it.  Going back to a colder, slower rise may help change that.  (Could also eventually try adding a small amount of buttermilk to spike up the lactobacillus content, but that may be scary!)

Mini Oven's picture
Mini Oven

Drop to feeding less flour and make it wait out the 12 hours.  Raising the acid in the starter to slow down the yeast.   Or tuck it into the refrigerator an hour after you have fed it but give it a day or two before taking it out again to finish maturing before using or feeding.  A few feedings like this should slow it down.


diah's picture


Acturally I don't really understand what is a 'starter'. What is the different using yeast dry and a starter. Which of them is good and healthier. And can I have the recipe on how to make a starter. I am really new to all this and just don't get what you guys talking about when you all saying using starter and using yeast. Please help me I am confused and blank.




LindyD's picture

Hi Diah, 

People use the term starter when they are speaking of a sourdough culture, which is created by mixing flour and water, which naturally ferments and ultimately produces a culture which will raise your bread naturally and give it a tasty acidic tang.

While there is wild yeast in your environment, the flour contains a good amount as well.

You can learn how commerical yeast is manufactured here

If you haven't baked bread before, you can get a good start by reading TFL's Handbook (see the tab at the top of the page) and making a couple of loaves using commercial yeast.

Or you can jump into the pool and create a sourdough culture.  Here are a couple of links to explore, one from Wild-Yeast and the other posted here at TFL

BTW, welcome, and happy baking.