A Starter’s Life
I wanted to post a small piece on what the life of a starter was, what I tend to refer to as its Feedcycle because lifecycle seems to suggest birth and death and that’s not the case. A quick disclaimer though: I’m not a biochemist, this is mainly discovered through experience. I do however have an accurate PH probe :)
Here is a video of the typical Sourdough starter you will construct in a lesson. It’s fed purely Stoneground Wholewheat. It has a ratio of around 1:2:2.5 or 1 part starter from last feed cycle, 2 parts water, and 2.5 parts fresh wholewheat. That means it’s a fairly stiff starter which is good to begin with because it’s easy to see when it needs feeding as it gets more liquid as it moves past its peak.
The starter goes through a pretty repeatable Feedcycle where upon being refreshed with new food and water it gets a bit shocked and does not much, the Lag phase. Then it starts to expand its populations of both bacterias and yeasts, and builds a lot of gas, the Build phase. This gas raises the starter in the jar because the gluten in the starter is trapping the gas, unlike Cola or Beer where the gas just percolates out of the top. This building of gas tends to look like it stops after around 8 hours (in my case, at my temp) but actually that’s not fully the case, this is the Peak phase. For sure there are finite nutrients in the starter, and also as the bacteria and yeast populations increase exponentially then some of their byproducts and processes cause the environment to be less conducive to population growth and more of the nutrients are spent on just staying alive. The starter is also now less stiff because some byproducts have weakened the gluten so much so that the starter becomes liquid and (as you can see towards the end of the video) the bubbles of gas can now percolate out of the starter just like Cola, the Fall phase.
The video below shows all those phases over a 12ish hour feed cycle. This isn’t what every starter does: this is what my starter does at my temp with my ratio of old starter to new food. Even day to day a starter will perform slightly differently, but generally for my set of circumstances (the ones we teach in the classes) it doubles in around 7-8 hours, peaks for around 2 hours then falls.
You may see some folks saying “my starter triples in volume”. For sure, this means they have a very active starter, but it doesn’t equate to a better starter necessarily, and that’s probably (but not always) down to gluten’s role. Gluten is like the latex of a balloon. A starter behaves much like bread dough, except without the salt, in that gluten forms and holds gas as bubbles. Gluten forms and somewhat conditions itself. Conditioning - when liquid hits wheat flour, then proteins combine to make gluten. It’s like suddenly millions of shards of latex are in your mix/dough/starter. Some of these shards, over time, gather together and form balloons, not very strong balloons, but they can contain gas. Gas- mainly Carbon Dioxide, that is a byproduct of the fermentation that the starter is working on. So your starter is making gas pretty much constantly after the Lag stage. Even when it reaches the Fall stage and the gas bubbles start to dissipate, it’s still making gas, it’s just that there is little gluten (balloons) left to trap that gas, so it effervesces out of the top of the mix as a light foam.
So let’s go back to “my starter triples in volume” - we tend to just lightly mix our starter ingredients. This means that gluten can’t form strong bonds on its own, and thus the “shards of latex” mainly just stay as shards. However, if we vigorously stir/mix/knead our starter after feeding, then the starter will form very strong gluten bonds - it will form many very strong balloons. Now the majority of the gas the fermentation produces cannot escape these millions of strong balloons, and therefore the starter will appear to rise much higher than double: even triple or more.
Once the starter is introduced to the bread dough mix then all that trapped gas is lost, therefore the amount of trapped gas has no tangible benefit to the bread end product. Your starter wants to look lively and active that’s the key, don’t worry about doubling or tripling.
Here’s a cool experiment. Feed your starter and then put a very large Ziploc in place of the lid, with an airtight rubber band around the neck. Now watch the gas that gets pumped into the Ziploc. This is a way better indicator of starter activity. Being a little more scientific, we could add a small fermentation bubble lock on the top of the mason jar and then time the bubbles. As long as the temperature is the same, the feedstock (flour type and water) is the same, the ratio of old starter to new feedstock, and the amount of starter in the jar is the same, then the bubble count would be a fairly accurate method of testing starter activity.
There is one further thing happening here that is difficult to see or test, but easy to smell and taste. During the Build phase your starter is making lactic acid (think natural yogurt smells and flavours), but toward the end of the Build phase, through the Peak phase, and absolutely in the Fall phase it transitions to making more acetic acid (think sour sourdough, and vinegar smells and flavours) and less lactic. It’s the acetic acid that destroys gluten, that’s why the starter falls, because the gluten balloons are destroyed. Wheat flour and water (without gluten present) is more of a liquid than a solid.