Frequently Asked Questions
Moving forward, many of the questions that you ask will be the driving force behind new directions and new research questions. We will continue to add to the list as we receive new questions. So keep them coming, but please do check here to see if your question has already been answered!
- Characterizing starter
- Educator Resources
- Experimental Design
- Flour type
- Indoor/Outdoor Experiment
- Microbial Ecology
- Using sourdough starter
- Wild Sourdough
Mistakes happen. Please send an email to firstname.lastname@example.org with the changes you need to make.
A failed starter can be humbling and discouraging – but it’s still scientifically important! Anecdotally, we know that starters DO fail sometimes – but we don’t yet understand the reasons why. This is partly because folks may not want to share their failures, and partly because there are so many different factors that contribute to a sourdough’s success, that it can be difficult to pinpoint the root cause of failure. By controlling for the age, environment, flour type, and the ratio of inputs (by using a single standardized recipe), and by claiming your failures, we hope to determine which factors might put a sourdough starter at greater risk of failure – meaning, hopefully, we can help you prevent other failures in the future. And we will add, make sure you are giving your starter enough time, the microbial succession process can take time (usually at least 14 days). Many folks give up on their starters prematurely!
We’ve asked you to transfer your starter to a new jar on day 15 to ensure that you (and we) can get a clear visual of maximum height and bubble production. After you’ve submitted your data and pictures on day 15, you can maintain and use the starter(s) however you like! (For this project, we are focusing on the first 15 days, only.) The easiest thing to do, will be to maintain only a single starter; although, if you grew starters using different flours, you may choose to keep them, to maintain any distinct characteristics.
The Wild Sourdough Project is a new, separate effort from the original global sourdough project, with the goal of addressing different questions. Most importantly: we want data about NEWLY GROWN starters (not pre-existing, old, or revived ones), to eliminate any differences in age or travel histories among starters.
We chose to provide our protocol and recipe in volume because we suspect that more people have measuring spoons at home than scales. That said, it is certainly possible to convert a recipe from volume to weight; but each participant would have to make this conversion, separately, for each flour and starter. (This is because the density of each flour varies – so 1 tablespoon of all purpose flour will weigh a different amount than 1 tablespoon of whole wheat flour – and so on, across different grains and perhaps even across different brands of flour.)
The dry layer may be unavoidable in some cases. The only reason we would absolutely recommend discarding a dry layer is if it has a lot of (fuzzy) mold growing on it. Otherwise, just go ahead and mix it back in. We do NOT recommend a solid lid, since this might prevent colonization by environmental microbes, though (of course) we don’t know the consequences.
If you live in a really dry climate (or in a cold climate and have the heat on full blast) you can use a little bit of extra water (up to ~¼ tsp) when you feed your starter.
Of course, the dry layer itself could potentially impact the ecology of the starter too. For example, Pichia kudravzevii likes oxygen so usually accumulates at the top of starters with O2 exposure (or in starters with lots of mixing). The dry layer could prevent environmental organisms/O2 from coming in. So if you do have a starter with this layer, just make note of it when you submit your data. So if you have a dry layer, dont worry about it too much, but please DO tell us about it in the “Extra notes” section when you fill in your data. This will give us an idea of how common this phenomenon seems to be.
For this project, we are focused on characterizing starters grown from only flour and water, so we can determine which “behaviors” (i.e., rise or aroma) might vary according to flour type or inside/outside conditions. Adding other yeast sources will “muddy the waters”. You’re welcome to experiment with other yeast sources on your own time; but we prefer that you NOT share those data for the Wild Sourdough Project.
You will feed your starter 14 times. The day you first mix your flour and water is Day 0 (we aren’t counting this as a feeding). Day 1 starts 24 hours after you first mixed your flour and water and you are ready to remove some and add more flour and water.
We just added a recipe to the Wild Sourdough page! For maintaining your starter, we partnered with NCSU Extension to create instructions and you can find them here: https://www.youtube.com/watch?v=6ePV91WPq48
Don’t despair! You shouldn’t expect a stable starter for at *least* ten-fourteen days. In that time, a lot is changing within your starter. As acids (produced by the Lactobacillus bacteria) build up, they start to kill other microbes. Sometimes these microbes are dominant in the starter for the first few days and can make a starter appear to be colonized by bubbly yeasty goodness, when in fact they are simply other microbes that are producing carbon dioxide. As acids build up, they will suppress other microbes that are producing carbon dioxide – that is until the acid tolerant yeasts have a chance to build up as well. So dont give up yet. Keep discarding and feeding your starter!
Just give the two some distance. Don’t let the starter you have fade.
One of the questions you will answer when you enter you data will ask about current sourdoughs in your home. This will help us tease apart any strange data anomalies.
RRD: Yes. This is really one of the remarkable things about starters, you can make them with many, many, kinds of milled grains and they converge (much of the time) on very similar microbial communities. To me this is as close a thing to magic as there is in the world. Well, this and spitting spiders.
The only flour type we don’t recommend is self-rising flour, since this flour has baking powder and salt added to it.
You certainly can, but be warned: many starters haven’t reached their full, glorious bread-making potential before 15 feedings. At that point, a starter is considered “mature”, with a stable microbial community full of acid-producing bacteria and acid-tolerant yeasts that leaven and flavor your bread. Before that, the community is changing daily in a process ecologists call “succession”. Just as a bare patch of dirt will grow grass and weeds, then flowers and shrubs, and eventually a forest (that transitions from pines to hardwoods), the “microbial garden” in your sourdough starter undergoes some pretty drastic changes in its early life. You can “measure” these changes by smelling your starter and recording its height every day. Different microbes perform different functions; so, as the community grows and changes, you will notice that your starter grows and behaves differently, too.
So – if you want to bake with your discarded starter, feel free – but don’t expect a particularly tasty loaf of bread in the early days. (Without a healthy community of yeasts to leaven the bread, your loaf may seem more like a rock cake.) But, in case you’re still interested to compare the bread your starter makes over time, I developed a “tiny loaf” recipe (on page 2 of Dr. McKenney’s easy sourdough recipe) that uses 1 tablespoon of discarded starter.
Not yet. It may be tempting to start using the starter now, but for now, keep doing the daily routine of discarding and feeding. A functional starter is dominated by lactobacillus bacteria (which produce acid) and acid tolerant yeast. Before the bacteria start producing acid, other microbes are competing with the yeasts. These microbes, often molds and unwanted bacteria, can often also produce carbon dioxide and cause your starter to bubble up. But they are tricking you. Told back from the temptation of baking with your starter just yet. From our previous work we know that very few starters reach their stable state before day 14, even fewer reach it before day 10.
Sourdough starters produce hooch when they are hungry. (After the bacteria and yeast have consumed all available sugars and starch, the yeast get stressed and start to produce alcohol.) The same way that you might feel more or less hungry on different days, we suspect that sourdough metabolism may change over time – making it more or less likely to produce hooch.
**You should always feed your starter at least once a day (i.e., every 24 hours). After a few days, when you notice that the starter is consistently falling from its peak rise (i.e., high tide mark) and producing hooch after 24 hours, you should start feeding your starter twice a day. Feeding more often may provide enough nutrients that your starter stops producing hooch.
We appreciate your enthusiasm, but we would prefer that you stick to the “recipe” if you want to contribute data to the project. Bigger starters generally have smaller surface area (and therefore smaller exposure to environmental microbes in the air) compared to smaller starters. Making all starters the same size, from a standard recipe, will help to control factors that might “muddy the waters” so that we can more clearly determine the effects of geography and flour type.
Please do the procedure on your next feeding, and make sure to clearly mention this (and indicate which number feeding you are characterizing on) when you report your data
We prefer that you stick to one type of flour per starter for the first 15 feedings; but after you submit your data, you can feed your starter whatever you like. As with so many other questions, there hasn’t been any formal research into the effect that a “change in diet” might have on the microbial community or behavior of a sourdough. But, anecdotally, many bakers have shared that the same sourdough starter might act differently when fed different types of flour.
Unfortunately, for the purposes of our experiment, we wouldn’t be able to use the data from such a starter. However, if you decide you just want to get baking ASAP and decide not to contribute data to our experiment, you can certainly try putting your starter in the fridge while you are gone. The cold will slow down the microbial activity, so they will use up the starches and sugars more slowly, but will not kill them. Just make sure to feed your starter before you put it in the fridge. When you get back, take it out of the fridge and pick up where you left off. But again, you just wont be able to share your data with us.
We are still investigating all of the microbial species we have found in sourdough starters. Stay-tuned, as we expect to publish these results in a scientific journal within the year.
We suspected that some folks might have issues with nosey outdoor animals. For the purposes of our experiment, I think a failure that is clearly due to interference by a sneaky animal might not tell us much about the microbial world. We will still be able to use the data from the starter you are maintaining indoors, even if you don’t have an outdoor starter to pair it with
We LOVE that this question has been asked more than once! Our answer: a very resounding “YES, please”!
Some starters need to be feed three times a day (i.e., every 8 hours) – particularly when the community is healthy and environmental conditions (i.e., warmer temperatures) promote high activity.
Of course! You can find all of the information you need in order to participate here: http://robdunnlab.com/projects/wildsourdough/ you will also find the link to submit your data.
Indeed, one of the questions in the data entry portal will ask you for the diameter of the jar. Ultimately, we want to calculate the total volume rise. As long as we know the diameter, starting height, and ending height, we can get a sense of the leavening. As for whether the diameter of the jar actually impacts the ability of microbes to colonize the starter: we dont know! But its a really interesting question and really gets as some of the basic ecological principles of dispersal and colonization. My hunch is that a very wide jar would mean a very thin layer of starter and therefor a greater surface area exposed to air. In addition to being more accessible to colonizing microbes, it might also impact the ratio of anarobes (the kinds of microbes that dont require oxygen) to aerobes (those that require oxygen, and would therefore only survive on the surface).
I think the question here is what we are actually expecting to be able to glean from the data. We do not presume that anyone is using sterile technique for this experiment. On the contrary, we expect microbes from the environment (air, water, cooking utensils,- even bodies!) will factor into the microbes that colonize the starter. We have done more controlled experiments (on a necessarily much smaller scale) where we had bakers make starters using flour from the very same batch of flour (http://robdunnlab.com/…/belgian-sourdough-experiment/), to address some of these issues. Experimental design is always about tradeoffs. We decided to opt for the design with the lowest barier to entry, so as to have the most amount of data. When you have a little bit of data, a little bit of variation matters a lot. When we have a lot of data, we have more statistical power, and so a little bit of variation is more acceptable. We could certainly try a follow-up experiment in which people keep two starters, both from the same flour, discarding and feeding for the first four days on one, and not disturbing other! Id be very interested to see those results!
RRD: For sure. We love experiments. Try any grain, or acorn four if you have it. Hazelnut. We’d love to know.
The only flour we don’t recommend is self-rising flour, since it has baking soda and salt as additives.
Your best bet here would be fermenting your loaf at a cooler temperature for part of the process, or refrigerating your starter for some time in between re-feedings (i.e. feeding your starter at 6am, letting it rest at room temperature until 6pm, refrigerating in overnight, and then taking it out of the fridge to use at 6am the next day). The recipe we have included as our basic sourdough includes this step. In terms of science, what is happening when you do any of these practices is you are aiming to slow the activity of bacteria (which make acid and enjoy warm AND long fermentations). If you utilize a refrigerator for any part of the process, you help to slow bacteria and acid production.
You can also avoid an overly sour sourdough by consistently re-feeding your starter every time that it “deflates,” (ie. not letting it go hungry) and by making sure that you don’t bulk ferment your loaf for too long. These steps help prevent the acidity from essentially “building up.”
Nope! We will likely start consolidating data and doing preliminary analysis during the summer. If data rolls in throughout the summer, we will likley be able to incorporate it.
Indeed! One of the questions you will answer when you fill in your data is about the temperature in your home. For starters outside the home, we can pull climate data from national databases, hence our question about your rough geographical location.
Thanks for pointing this out. Yes, chlorine will evaporate, but chloramine will not. We have gone ahead and added an additional question to the data entry so that folks can enter a little more information about their water source. It will not necessarily get at the choloramine issue, but will help us tease apart the results. If you DO know that your city treats your water with chloramine, id recommend using bottle or filtered water instead. You can certainly boil your water, if you like. Just make sure to let it cool before using it.
RRD: Good question. You can always make the outdoor starter and bring it in when it is below freezing. The truth is we don’t know what happens to starters when it freezes repeatedly. Some species will die, but others won’t. It also makes me wonder what people did a thousand years ago in cold environments with their starters.
I’m particularly interested in the temperature of the water we add, as in my limited reading (complete noob here), I’ve seen that in addition to the obvious effects of ambient temperature on the culture’s metabolism, the temperature of the water (particularly for the initial mix maybe?) can have a big effect. I’d like to start the little ones off with the best they can get, but I also understand the importance of uniform procedures. So I ask, does it matter for the experiment you’ve designed? I might just do one room temp and one closer to ideal just for my own edification, but it’d be good to know if the experiment requires the room temp for good data! (Q from Nathan Staffa)
LMN: Really good points! This is what we love about this: we could do a whole separate experiment just to explore these questions! Given our directions, we assume most will use room temperature water. SO using room temp water will give us the best comparison to other’s data. But, if you want to use slightly warmed water, you can do that. Make sure to note it in the “other notes” section when you enter your data. But making two starters, one with warmed water and one with room temp water, would be really neat! We would certainly be interested in the results.
RRD: Our lab is closed now (as are all the labs we depend on). Once they re-open we will be sequencing a subset of starters from this new phase of the project and a handful of old starters from around the world that help us fill in some gaps in the Global Sourdough Project (e.g., Africa).
EAL: This is something that we’re interested in understanding better. We have good evidence that starters can remain relatively stable over time in terms of the species of yeast and bacteria that are present, but we haven’t measured how individual species are evolving genetically.
AAM: We have a number of research projects underway. Some of the findings are published, some are available in a preliminary form, and some are still being investigated. Stay connected with our social media sites and newsletters to hear more as we continue to share our findings. In the interim, we suggest reading our research paper on the connections between bakers’ hands, ingredients, microbial communities, and flavors of bread in this paper: https://msphere.asm.org/content/5/1/e00950-19.abstract or visit our interactive website to view the species of yeast and lactic acid bacteria we found in individual sourdough starters across the globe: http://robdunnlab.com/projects/sourdough/map/. Want to get to know these microbes beyond their names? Visit the website of one of our team members and meet these beautiful yeasts: http://microbialfoods.org/yeast-profiles/.
AAM: In our world of the internet of things we have an unprecedented capacity to measure our own activity, be it heart rates, sleep rhythms, or hormone cycles. One could very well imagine a future where we co-opt this technology and sensor systems to help your bread communicate with you. To give it the ability to tell you when it needs to be fed, how acidic it is, and whether it is ready to be used for baking. But, as a society, we are not there yet, and like all technology advances these would present both opportunities and challenges. In the absence of having “smart bread,” we look forward to working with you all to find improved ways of measuring aspects of your sourdough starter and bread and in turn, measuring the activity of the microorganisms inside of them. For now, we remain excited that the current methods for making a starter and measuring sourdough activity require a tiny bit of flour, some water, a few spoons and jars, and one of the most sensitive pieces of equipment on earth for detecting aromas: your nose.
LMN: Make sure to check out Anne’s mini-seminar scheduled for June 11th: Baking Yeasts of the Future: Where to Discover Them and What They Can Offer
RRD: YES! Absolutely. We have created additional resources specifically geared toward teachers that you can find here(they are hosted on our education focused site, StudentsDiscover.org). We are super dedicated to helping students at any time, especially now. So also let us know what you do in the classroom and what else might be useful for the students.
Martha: Absolutely. In the scientific literature, sourdough has been studied in various bread-like products, like Ethiopean injera, lavash (western Asian origin), and pizza (Zolfaghari et al., 2016; Gaglio et al., 2018; Fischer et al., 2014). But, there are hundreds of recipes out there for sourdough “anything.” Sourdough pancakes, sourdough waffles, sourdough granola bars, sourdough donuts, sourdough brownies, sourdough muffins, sourdough biscuits, sourdough bagels, etc. Oftentimes a little bit of sourdough is even used to make laminated pastries, like croissants! When you use sourdough and let whatever you are making sit for a while before cooking it, you use sourdough as a leavening agent. But, if you put a scoop of sourdough into banana bread (for example) and then immediately bake it, sourdough acts as more of a flavor-enhancer.
EAM: Sourdough starters (especially those made with whole grain flours) contain minerals including potassium, phosphate, magnesium, and zinc. However, phytase and other plant compounds in flour bind these nutrients, preventing us from digesting them. The microbial digestive enzymes and low pH in sourdough starters both work to degrade phytic acid, releasing those micronutrients and making them available. In addition, the microbes produce folate (a B vitamin).
RRD: Great question. We didn’t receive any samples from Africa. Once our lab re-opens, we’d LOVE to begin to gain a better understanding of starters in Africa. More generally, we’d love to better understand the diversity of kinds of starters outside of those employed just for bread.