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worried about acetone smelling starter, doing a side by side test, should I toss out the acetone smelling starter

Jimmy Blob's picture
Jimmy Blob

worried about acetone smelling starter, doing a side by side test, should I toss out the acetone smelling starter


I am new to this forum, as well as to sourdough starters.  I could use some advice regarding whether I should keep my acetone-smelling starter, a result of me missing two feedings -> cutting from 2X/day to 1X/day on back to back days.  And any other tips welcome.

Our (my kids and me) first starter didn't work out.  I used 1:1 ratio with 50g rye and 50g water.  It seemed like my flour was super absorptive because the mixture was a very thick paste.  We gave it a go over 5-6 days and with little change, we tossed it.  I learned here my starter was getting too much air, as it would form a thick skin on the top, so now I cover with plastic wrap.

Our second starter, Apr 30 (1 month ago), I decided to aim more for the consistency of "thick pancake batter" rather than the 1:1 ratio I read so often about - that placed us around 50g rye and 80g water.  There was a fit of activity at the beginning, then some 20-30% growth in volume Day 3, 4, 5 and then poof on Day 6, it doubled.

Things were chugging along, it would almost double to triple, but has never passed the float test.  I eventually cut down volumes to save on discard, to 10g starter, 10g rye, 12g water.  Then Monday and Tues last week, work got busy and I missed the morning feed two consecutive days, so the starter only got the evening feed.  Immediately, the starter reeked of acetone.  I've read enough in these forums to know it was due to underfeeding and feel pretty guilty about messing it up. 

To fix the acetone smell, the last 4 days:

  • I tried feeding it slightly more (though I now see in forums recos to feed it 1:4:4 or even 1:5:5) to 10g starter, 17g rye, 19g water.  Twice a day.
  • I also left it covered a little looser - and did notice the smell would dissapate some, but it would be back after re-covering for some time.

The starter would still double (not triple), but the acetone smell was ever present.  Not as strong as when I originally underfed, but present in a way that made me wonder if I had negatively shifted the yeast and bacteria ecosystem.


This weekend, starter now 1 month old, I had some extra time, so wanted to give it a shot at baking sourdough bread.  I followed this recipe: with bread flour.  Deviations

  • Leaven step - I noticed in the morning, the smell was sour, but not very bubbly
  • Autolyse step - I let it go four hours, figuring more flavor was better.  I wonder whether this was too long, especially since I went long on following step.
  • Folding step - The recipe suggested six folds, for a total of 2 1/2 hours.  I had in my mind six and not 2 1/2 hours, so I ended up folding for 3 hours.  It didn't look like there was much inflation here.
  • Proofing step - I put one of the two balls in the mixing bowl on the counter to proof for 3 1/2 hours.  The other ball in the fridge for overnight proofing.  When the 3 1/2 hours was over, it didn't look substantially different, so I figured there was going to be little rising action.
  • Dutch Oven step - My husband pointed out when we put the second ball in, as I was explaining the importance of steam, that our Dutch Oven doesn't seem to seal super well. 

Indeed, the bread did not rise much, though it tasted well enough that the kids asked for thirds.  Ball 1 (rm temp proofing on left).  Ball 2 (overnight proofing in fridge on right).


I am wondering if the lack of rise is because the starter has become too acetoney, or if it is because I overproofed it, or something else?

To do a side by side experiment, I fished out some starter discard that I had accumulated in the fridge, likely from over a week ago (I didn't keep discard from when the starter smelled like acetone - too scary) and did the same 10g starter, 17g rye and 19g water for both.

On the left is the "Current Acetone" starter. On the right is the "Old" starter from a week ago.  This is a picture 9 hours after the morning feed.  The top of the tape is where the starter level starts at.  I notice that the current "Acetone" starter has not yet peaked, whereas the "Old" starter from a week ago is already sliding down. 

  • At this point, the "Current Acetone" starter smells like acetone, I can't smell anything else because it's quite overwhelming. 
  • The "Old" starter smells a little like alcohol (not acetone) but I can still smell something sour underneath.

I figured it'd take a few days to get the refrigerated starter back to full strength, so I plan on doing this side by side for a few more days.


Could you give me advice about

  1. I'll wait a few days for the "Old" starter to get back in shape, but if it goes well, would you recommend throwing out the "Current Acetone" starter and move forward with the "Old" starter? 
  2. Should I be feeding a higher ratio of flour and water?  I naively thought all sourdough recipes asked for 1:1:1, but am starting to come across much higher ratios, like 1:5:5.
  3. Considering this is rye flour, should I be increasing the water?  See the consistency in second pic (sorry, I can't seem to get it flipped the right way, even after multiple tries).
  4. Any other tips on the sourdough bread baking part welcome as well!

Thank you so much for offering your time to help a newbie, I really appreciate it.


andykg's picture

the acetone smell is fine, it just means the starter is more sour and hungry. If you dont want an overly sour starter feed it more often using cooler water and a lower temp fermentation, otherwise feed like normal and you'll find the smell goes until its hungry again.


Jimmy Blob's picture
Jimmy Blob


Thank you both for your advice.  I wanted to report back on my A/B testing after a few additional days (now 6 days since missing morning feed on back to back days):

  • Ace, the current acetone-smelling starter, still smells like acetone, but it isn't as overpowering of a smell.  
  • Original, from the starter I fished out from the fridge from before acetone, smells slightly acidic but I can smell sour rye underneath it. 

My observation is that Original seems to be peaking later, but also sliding down a bit earlier than Ace.  

I'm inclined to do one more day of this A/B testing and if it continues well, I'll probably pick going forward with Original because it seems to double as well as Ace, but smell better.

For those of you with more experience, is there any advantage/disadvantage to a starter that peaks later, but falls faster?  Thank you kindly!

Some pics (sorry, I flip it before uploading, but it's not cooperating)

June 1 9am (right before first feed of day, Ace on left, Original on right)

June 1 4:30pm (7.5 hours after morning feed, Ace on left, Original on right).  Orig is still rising.


June 1 9pm (right before second feed of day, Ace on left, Original on right).  Seems like Original feel further

June 2 9am (right before first feed of day, Ace on left, Original on right).  Similar pattern of Ace holding onto its rise better.

June 1 6pm (9 hours after first feed of day, Ace on left, Original on right)

phaz's picture

By the numbers

  1. Keep the healthiest, unless you want to keep more than 1 starter, then keep both. 
  2. How much to feed is all up to the starter and how much time you want to spend taking care of it. More active the starter, the more food it needs and/or the more often it needs it. You can play with the ratios and times and find a combination that fit into whatever schedule you choose.
  3. I tend to keep starters a little on the thick side. It's harder to see bubbles and rise when to thin and thicker seems to last a little longer between feedings.
  4. Tips - experiment (you'll find lots of ways of doing something), see what fits your needs, make lots of bread. Enjoy!
Jimmy Blob's picture
Jimmy Blob


Thank you for the advice.

  1. Yes, planning to keep the better smelling one, assuming both perform the same.  See above comment asking if there's any advantage/disadvantage to choosing the one that seems to peak later, but fall faster?
  2. My plan is to keep with the 2X/day schedule.  I'm feeding roughly around 9am / 9pm.
  3. Thanks for letting me know that the thickness of my post-feed starter seems ok.
  4. Yes, the plan is to make bread this weekend again =)!!
phaz's picture

Which to keep - either one really. I believe they are or will be the same after a little while anyway. You're probably just seeing the difference between a healthy starter and a not quit as healthy starter. With regular feeding they most likely will end up the same beast. Enjoy!