Sacrificing upwards of 50 g of flour per day to the levain gods isn't really a sustainable model, nor is it convenient - eventually we'd like to get back to a regular schedule, right?
So, how do you put your bread adventures on hold, without needing to wait 5-6 days to start a new culture of yeast from scratch? People often throw their starter in the back of the fridge in a glass jar to sit in timeout, right next to the bread and butter pickles that you regret buying because B&B are absolutely disgusting. Don't @ me. But if your fridge is at all unlike a professional kitchen's (read: a superposition of controlled and uncontrolled chaos), you'll forget about it. For weeks, or at worst, months, you'll have a still slowly fermenting jar of flour sludge (alas! is that mold also? can we bake mold? *frantically Googles*). You can certainly do this if you know you'll be back on the sourdough train within a week or two - hey, we all need breaks. Any longer though, and you'll need to almost pay more attention to it than if it were freely fermenting on your counter. You can read conflicting answers on how to store it in the cold recess of your fridge: open top, tight lid, only cheesecloth, cheesecloth plus a rubber band, cheesecloth with a layer of parchment as well, cheesecloth with the blessings of Martin Luther himself. And truthfully, you've already had a cold fermented loaf before - you know the yeast doesn't just stop being active at 35-38 deg F. It will keep fermenting and accumulating excess acidity in an uncontrolled fashion. So what's the point? What's the solution?
Don't put your starter in the fridge.
At the point where you have a healthy sourdough starter (i.e. it can easily double in volume after feeding over the course of 5-6 hours), you'll have excess. The discard. You've seen the bakers on the 'gram making everything from sourdough pasta, to sourdough pie crusts, to sourdough biscuits, sourdough liege waffles, to sourdough hair ties. I generally do not fall into this camp of what I do with my discard. I cannot sustainably eat or store the baked goods that you can make from an every day discard schedule. I'm sorry, sometimes I just don't want discard pancakes - read: very often I do not want discard pancakes.
But Cas, that seems supremely wasteful to just throw away the flour and water mixture resulting in a yeast colony that you worked so hard to cultivate by doing absolutely nothing but awaiting the cruel passage of time, right? Right. You can toss it. I'm not going to judge you, but remember, the more you throw away when you aren't under the explicit plans to bake loaves of sourdough within the next several days to a week, the more flour you wind up wasting in the long run.
That was merely an aside to the true argument I want to make here: dehydrate and freeze your starter. What are the chemical and physical process that are keeping your yeast colony alive? The presence of liquid water and above freezing temperatures - you know damn well it's harder to make a new sourdough starter in the winter than it is in the summer due to differences in ambient temperature. Solve this problem by spreading out your discard (or your entire ripe levain) onto a silicone mat as thin as you can - I use an offset spatula to aid with this. It'll get sticky, but whatever, you were going to throw the starter away anyway. Let this sit out, uncovered, in a dry-ish room temperature location in your house. If you have a crafts room, feel free to use that, but you'll need to make sure it goes undisturbed for 2-3 days while it completely dehydrates. If you were to somehow suck all of the water content out of your starter, it would surely kill it, but by slowly starving it of water, the colony sacrifices parts of itself to save the whole (maybe the analogy here is broken, but hopefully you get what I'm talking about). Smooth gradient dehydration. Don't try to speed this up in a warm oven or anything, let nature do its magic.
Once you can easily pick up the sheet of dehydrated starter and snap it like a Christmas cookie, do just that. Break it up into tiny chunks like you're reenacting the one scene from Breaking Bad, you know...the one where they make meth. Weigh out the starter and place into a freezer bag, and FFS, label the bag with how much you have, it'll make your life much easier. Toss that bag into the freezer. Congratulations, you've now preserved a portion of your culture that you took so long to make in the first place (unless you were gifted an already ripe sourdough).
But the temperature!! Won't this kill the yeast)? It will not. Commercial yeast production facilities essentially flash freeze and coat their yeast with a protective barrier to place into those nice little packets. Recall that the yeast SLOWS DOWN at fridge temperatures, but will essentially go dormant at near-zero deg F temperatures. You can now call yourself a preservationist for your lactobacillius.
When the spark of sourdough strikes you again, or for when you have another protracted length of time when you're home for say, a pandemic, you can start your addiction much quicker than going from scratch. And is much less of a pain than taking up precious fresh food storage in your refrigerator.
Simply take 30-40 g of your broken chunks of frozen starter and place into a jar with equal parts room temperature water. Let that sit for 2-3 hours and give it a stir to make sure your chunks are well hydrated. If you smell it, you should already be getting whiffs of acidity and sourness. Once you have a tahini-like consistency in your starter, give it a small feed (if you normally feed 50 g of flour and water each day, go with 25 g on this first one), and check back in after another 4 hours. If there isn't any activity, let it go another 4, or until you start to see activity and bubbles popping on the now ideally domed surface of your starter. After 2 subsequent days of regular feeding, your starter is now ready to be baked with for full loaves of bread. Record time, if you ask me.
For testing purposes, I have now successfully revived frozen, dehydrated starters 3 times, all from the same mother starter at regular intervals (after 6 months, 12 months, and 18 months). They are all winners. I have some data to show a side-by-side of how a frozen starter and a fresh starter compare at the same time interval. 5-6 days on average for a fresh starter; 2-3 days for the frozen one. The math is there, folks.
As a closing remark, I want to remind you of the crucial second element: temperature. Your dehydrated starter will fizzle out in activity if you do not put it into your freezer. I conducted an experiment where I took the same dehydrated chunks and tossed them in my room temperature pantry and attempted a revival after 12 months. This did not work, even after several days of feeding. By then, the yeast is fully dead. I don't recommend this.
I have plenty of pictures to below that show the process of revival and dehydration process. Ask me if you have any questions or need clarification in the comments below, or email me at my contact page.
Comparison of two sourdough starters that were revived at the same time, each measurement on each day on the x-axis is at 5PM after an 8AM feeding schedule, identical amounts of whole wheat flour and room temperature tap water for both. (color online: frozen starter in blue, fresh starter in orange) Note: on day 2.5, I was able to measure the height over lunch, indicating that the frozen starter had reached its activity peak for the day and had sank down by the time I measured again at 5PM