The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Does rising sourdough starter always prove the presence of yeast?

kabeee's picture

Does rising sourdough starter always prove the presence of yeast?

I'm not sure if this has been asked before but I was wondering whether the fact that the starter could raise dough is proof it contains the correct yeast/bacteria for sourdough and is therefore perfectly safe to make bread with, or if there are other kinds of bacteria that could raise dough the same way that are either unsafe or won't taste very good. I know there are some bacteria that can make the starter bubble in when you first start it that are more or less harmless, but is there anything that would thrive in starter that is older that would simulate yeast by raising dough?  

I am new to making bread and made a sourdough starter following the directions on this site (flour and pinapple juice to start, then flour and water until it could raise dough to double).  The starter is about a month old now, although I haven't made anything with it yet.  Its been in the fridge for the last few weeks and gets what I assume is hooch on top if I forget to feed it for too long (greyish water that smells distinctly alchol-like).

The problem is I have never seen or smelled starter in real life and while the starter doesn't smell bad, it just doesn't quite smell like what I expected given how baked sourdough bread smells.  Its not moldy or oddly coloured or anything like that.  I just want to make certain that it is definitely sourdough starter and not a colony of something else that I am baking with so I don't waste flour, or worse make someone sick :)

Mini Oven's picture
Mini Oven

Start by pouring off the protective hooch on top and digging out some starter from the bottom layers.  About a heaping teaspoon.  The consistency can vary from soft dough to crumbly wet chalk like.  (Now cover & replace the old starter back into the refrigerator as back up starter while you feed and play with this new one.)  

To the scoop of starter:  Add 40g water or about 1/4 c and stir vigourously to break up lumps and get some air into the liquid.  Now add some flour, up to 1/2 cup (40g) to make a soft paste or dough.  Note the smell or lack of it.   Cover and let rise in a warm location.  (about 75° F to 80°F or 25°C)  

It may take a little time to recover after the long fast but give it 24 hours before you discard and feed.  Save a heaping teaspoon and repeat the above amounts.  Should no rising or bubbling occur after the second feed, wait another 24 hours.   Let the starter rise to the maximum height it will go and when it starts to level out or fall back, discard, reduce to a heaping teaspoon and feed again.   It may take about 3 days before it is ready to use in baking. 

Juergen's picture

Your starter seems to be just fine except for the fact that it is in a state of dormancy after spending a few weeks in your fridge. Revive it as per MiniOven's instructions. 

I'm not a microbiologist but I can assure you there is zero risk in baking with it. Somehow the 'good' colonies of yeasts and bacterias -those we need for sourdough baking-, thrive in a relatively warm environment of flour and water. Nature takes care of that.

kabeee's picture

Thanks for your help.
I figured the fact that it produced hooch, along with raising dough, was good evidence that I did actually have the right organisms living in the starter. I had done what you suggested to revive it, and the alcohol smell had gone, but the smell of the healthy starter wasn't quite what I expected so I wanted to make sure there was no risk that my starter was housing something else that just happened to act a lot like the yeast and bacteria I want. I'm about to make some dough with it now, so hopefully it will turn out ok :)

Thanks again!

Ruralidle's picture

Just to comment that, when you bake to an internal temperature of around 200F, there are very few strains of bacteria or yeast that will have survived.  That means that it shouldn't poison you :) even if it tastes unpleasant.

MaximusTG's picture

While what you say is probably right with regard to breadbaking, however, the presence of unwanted bacteria or other microorganisms and their absence after heating doesn't necessarily make it safe to eat. The bacteria might be dead, but toxins produced by them may survive such heating. 

Ruralidle's picture

Botulism being a case in point but the vast majority of such bacteria very rarely get into bread ot sourdough starters, so long as very basic hygene procedures are followed.

kmrice's picture

Clostridium botulinum is an anaerobic bacteria which produces the toxin, botulinum.  I don't know if this bacteria is likely to be present in a sourdoug starter, but, perhaps it could.

The bacteria itself won't hurt you; it is naturally present on many vegetables which are eaten raw. Being anaerobic, the bacterial does not produce the toxin in the presence of oxygen in the garden or in the house.

The toxin the bacteria does produce when oxygen is not present causes botulism, which is very deadly.

The bateria is fairly hard to kill. Canned foods which have not been adequately heated during processing may contain the live bacteria after processing. Since canned foods are sealed and lack oxygen, the anaerobic bacteria can produce the toxin in the can.

The toxin is much less hard to destroy and breaks down into harmless compounds when heated.

Thus, you don't get botulism from eating fresh vegetables, although the bacteria is often present. You also don't get botulism from eating canned foods which are brought to a boil before eating; any toxin is destroyed.

In poorly preserved foods, eaten cold, the bacteria may have survied the processing and produced the toxin in the can, with fatal effects.

The same foods, if brought to a boil, would be harmless. 

One big botulism outbreak involved vichyssoise. It was not properly processed, and the living bacteria in the cans produced the toxin. Since vichyssoise is served cold, the toxin was not broken down before the soup was eaten, with fatal results.

At bread temperatures of 180 f to 210 f, any botulism toxin would be broken down. I tend to think the bacteria itself would all be killed as well, and, if not, would not produce toxin since bread is not stored in an environment without oxygen. I've never heard of a botulism outbreak involving bread. Perhaps it could be a problem with canned bread.


Grenage's picture

canned bread


kmrice's picture

Actually, there is a canned bread which is regional to Boston. It has molassas and raisins and is sort of steamed in a can, or water bath. After cooking, the commercial product is then sealed. It can be made at home and can be pretty good. Sort of the same idea as fig pudding.