Cover with plastic wrap and and let ferment on the counter for 24 hours.
Day 2: Feed/Ferment
Add to Day 1 sponge 130g bread flour and 115g water.
Mix until well incorporated.
Cover with plastic wrap and let ferment on the counter for 24 hours.
Day 3: Feed/Ferment
Discard half of the starter.
Add to the remaining half, 130g bread flour and 115g water.
Mix until well incorporated.
Cover with plastic wrap and let ferment on the counter for 24 hours.
Day 4: Feed/Ferment/Finish
(See Notes)
Discard half of the starter.
Add to the remaining half, 130g bread flour and 115g water.
Mix until well incorporated.
Cover with plastic wrap and let ferment on the counter until doubled (up to tripled) in size, 4-24 hours.
Start the Barm - a 100% Hydration Sourdough Starter
Once the seed culture has doubled after the Day 4 feeding, you can start the barm.
Mix together well the 450g bread flour, 450g water, and 200g seed culture. Make sure all the flour is hydrated and the seed culture is evenly incorporated.
Cover with plastic wrap and let ferment at room temperature until bubbly (~6 hours).
Refrigerate at least overnight, and up to 3 days.
Your barm is ready to use as your levening in a sourdough bread recipe!
Maintain the Barm
The barm needs to be fed/refreshed every 12 hours if kept at room temperature. I recommend refreshing this frequently for the first couple weeks to increase activity. Eventually, you can store the barm in the fridge, and pull out to refresh 3-4 times once every month, or more often if you plan to use it.
Discard (or save for a "used starter" recipe like my sourdough crackers) all but 200g of the barm.
Add 100g of bread flour and 100g of water. Stir to fully combine.
Let sit 12 hours at room temperature.
Repeat steps 3&4 every 12 hours as long as you keep your starter out at room temperature.
If you do not want to continually feed the starter, you can feed, and then transfer to the fridge for up to a month. (I like to store 400g.)
At least 1x/month, pull out the starter from the fridge and let it warm to room temperature. Discard any accumulated alcohol on top, discard all but 200g, and then feed according to steps 3&4, 3-4 times, before either using or returning to the fridge.
Long Term Storage for the Barm
If you want to put the barm to "rest" for a period of time the simplest way is to dry some.
Give it a fresh feeding with equal parts bread flour and water.
Then simply spread a thin layer on a parchment-lined baking sheet and leave at room temperature until dry.
Break into pieces and store in an airtight container, in a cool dry place, indefinitely.
Return the Barm to an Active Starter
To begin, add 2x water by weight to the dried starter. For example, if you had 25g of dried starter, you would add 50g of water. Use a container that allows you to fully cover the dried pieces with the water.
Let sit for a few hours until the dried pieces are softened and you can stir it all together.
Add 1x bread flour (so 25g in this example).
Stir, and let sit for ~12-24 hours. You should start to notice some bubbling activity.
Feed again with the same equal amounts of water and bread flour (25g each in this example). Do not discard any starter at this time.
Repeat steps 4&5 until you have a bubbly and active starter, it should only take a couple times.
Once the starter is activate, discard all but 100g, add 50g of bread flour and 50g of water, and resume your regular feeding schedule by following the "Maintain the Barm" instructions above.
Notes
Before Starting Day 4 - The sponge should have at least doubled since the previous feeding on day 2. If it has not, allow it to sit out another 12-24 hours until at least doubled, before proceeding to Day 4.After Day 4 Fermentation - Once the starter from day 4 has at least doubled, you are ready to move on to the barm. The barm will become more active and flavorful over time, so keep the same barm going as we have done, and it will continue to reward you with better leavening action and deeper flavors.