Sourdough Starter Refrigeration Maintenance Protocols

^{Edited from an original post by Betsy Tranquilli in our public Sourdough Geeks Facebook Group on 30 March 2025, where Betsy is a valued Admin, Group expert and All-star contributor. When not volunteering for Sourdough Geeks, Betsy is the owner operator and fantastic baker at Makani Mills micro-bakery in Hawai'i. Follow her on Instagram @MakaniMills.}

At Sourdough Geeks, we strive to be a source of scientifically sound information to help guide you on your sourdough journey. Our ultimate goal is to help you become better bakers, if that is indeed your goal.

The foundation of everything is the sourdough culture we maintain.

We offer a number of resources already on best practices when it comes to sourdough starter care, including these two articles on this blog:  You & Your Sourdough Starter: Relationship Advice & Maintenance Guide & Hooch: To Stir or Not to Stir?  [Editor's Note: See FREE RESOURCES for plenty more on Everything Starter. We also offer a comprehensive Mastering Sourdough Starter Course.]

And if you’ve been here any length of time, you know that we acknowledge that the preponderance of sourdough science to date shows that the microbiome of a properly maintained counter fed starter will harbor stronger, more established dominant strains of species compared to starters that are refrigerated.

A while back now, James provided this excellent summary regarding fridge v counter maintenance, with cited studies, for those interested in the science behind the advice:

"There are 3 main reasons why I assert that it is best to keep sourdough starter refreshed regularly at ambient temperature:

1. We know from research that F. sanfranciscensis rarely appears in starters which are subjected to cold storage.* This is because the growth rate approaches zero at 4°C. This bacteria generally thrives in bakery cultures, establishing a dominant pairing with maltose negative yeast K. humilis, which is inactive at 7°C and below. 
   ^{See Modeling of Growth of Lactobacillus sanfranciscensis and Candida milleri in Response to Process Parameters of Sourdough Fermentation from Michael Gänzle, the Canada Research Chair in Food Microbiology.}
2. We also know from research that starters subjected to cold storage generally do not have the same leavening power as those which are not. Although some exceptions were found, here is a direct quote from the below study. “Overall, the tested methods of storage did not succeed to get reactivated sourdoughs with leavening capacity as high as that of unstored sourdoughs."
   ^{See Assessment of comparative methods for storing type-I wheat sourdough from Anna Lattanzi, Department of Soil, Plant and Food Sciences, University of Bari Aldo Moro, Italy.}
3. The writings of Ian Lowe, who is absolutely one of the preeminent minds in cereal fermentation, all converge on this observation: “If there’s one sourdough ‘golden rule’, it’s this: For best results, refresh your starter at least once a day, and always maintain between 20° to 30°C.
   ^{See Aphorisms, Axioms, Rules, Guidelines [...]} 

So ‘consistency’ in sourdough exists in a range, with the ideal range being 20-30°C (68-86°F), and the sweet spot generally in the middle, and the generally listed desired dough temperature (DDT) in a professional bakery setting.

Can you get results outside of this range? Absolutely.

Will the average home baker be able to distinguish differences anecdotally? Most likely not.

But if we follow the people who know more than we do, all roads point to the objective ideal of not using refrigeration in a sourdough system.”

*Specifically, we know that after 1 week, 99% of these Type I heterofermentative bacteria are dead in unfed (unrefreshed), refrigerated starters. And after 1 month, 99.9% are!  

Dr. Michael Gänzle (referenced above), is one of the top researchers in the world on sourdough microbiome. In 2021, he gave a talk at Johnson & Wales International Bread Symposium on “How to recruit Sourdough Microbes for Baking” that discusses the organism changes found in refrigerated starters vs. daily backslopped bakery starters. Watch in full here.

So while the science clearly points one way, this information should not be misconstrued to say that you can’t or even shouldn’t refrigerate your starter.

We understand people live in the real world. We understand that every person should have their own individual goals for the outcome of their own bread and it is not up to us or anyone else to define that goal for them.

What we can offer, though, is best practices for starter refrigeration that is most likely to produce the best outcome based on what the science and the best sourdough minds tell us.

As James mentioned, Ian Lowe, considered one of the preeminent minds on cereal fermentation who has served as a consultant at sourdough bakeries worldwide, has been a vocal proponent for counter-top feeding frequently (ie. at least once daily) and kept between 20-30c.

But in a 2018 interview with Bread magazine, Lowe spoke at length on starter refrigeration protocols.

“Refrigerating a sourdough starter isn’t a bad thing, but it’s not without a few caveats,” Lowe said.

The following is drawn from that article as a summary of Lowe’s protocol for making best use of the refrigerator to store a starter:

Sourdough Geeks Starter Refrigeration Maintenance Protocols

• Start with a healthy, active culture. Ideally, it would be recommended that upon establishment, a starter has several months of daily, room temperature feedings before refrigerating to ensure a fully viable and stable cell population.
• Do several successive refreshments before using to build the maximum cell population possible and boost the culture’s metabolic capacity. “The more refreshments, the better (three is good, five is ideal),” said Lowe.
  
  
• Before placing back in the fridge, refresh and allow the starter to ferment at optimal conditions (room temp), to begin building cell numbers before cold storage, during which all growth will completely cease. This can mean allowing the starter to ferment at room temperature for anywhere from 4 to 12 hours (depending on ratio fed and room temperature).
  
  
• Refresh at least on a weekly basis out of the fridge, even if you are not using the starter. This will maintain the established cell populations, particularly yeast, before they die out completely. “This will make using the starter for baking more convenient because of well-maintained cell numbers,” according to Lowe.

Let us know how you get on!