Why is baking soda included in sourdough cracker recipe?

Question

I'm following a recipe for crackers made with unfed sourdough starter (other ingredients are flour, oil, and salt). It also calls for 1/4 tsp baking soda and I'm wondering why since the dough sits on the counter several hours before baking, and can also be stored in the fridge for days. I would think the baking soda would no longer be active to work as a raising agent. Is it possible it is there for some other reason?

Am I correct that the baking soda is no longer active in the dough after so many hours before baking? If so, how can it work as a leavening agent?

I've added a photo of a cracker from the batch with baking soda. Not sure if the photo shows it well, but there's a big raised bubble in the middle, although hard to say if it's due to the baking soda or the sourdough starter. I'd say 80% of the crackers have a bubble of some sort. I read somewhere that baking soda might be used to make a more tender cracker and this batch is in fact not crispy (big disappointment). My next batch will be identical but without baking soda, so I'll see!

Answer 1

To answer the question in the second paragraph:

Baking soda is a chemical, sodium bicarbonate, not a microbe, so it is always "active" so long as it is still baking soda. Once baking soda is "activated" it chemically transforms into something else through an acid-base interaction. First, baking soda must dissolve in water. This is the important part! Acid-base interactions do not occur in solid form, they occur as solutions in water (not fully correct, but true enough for this answer). Without the presence of water, you won't have a carbon dioxide producing acid-base reaction.

Baking soda is NaHCO₃. The carbonate anion (HCO₃^-), once separated in water, can then interact with some other acidic molecules, such as those produced by the sourdough bacteria. Since sourdough (when present in water) will produce an acidic solution, there will be things for baking soda to interact with. The interaction of the carbonate ion will usually produce carbon dioxide (CO₂), and this is the gas that causes the desired rising.

Baking soda that is dissolved in water in an acidic solution will rapidly "activate"; mix baking soda and vinegar and watch the resulting reaction. But a dough is not a water solution, although there is water content present in it. Therefore, the rising action will not proceed immediately, it was wait over time as sodium bicarbonate molecules come into contact with acids in the presence of water.

Therefore, the rate of rising action you get from baking soda depends on several things; temperature, water content, acid content, and mechanical agitation (i.e. kneading). A cold, un-kneeded, low moisture dough with a poor sourdough starter will see very slow activation of the baking soda. A warm, wet, well-mixed dough with a very active starter will see very fast activation and rising.

Answer 2

In addition to leavening, baking soda increases the PH of the dough. Since your recipe uses sourdough starter, it may be fairly acidic. Adding baking soda will make the dough less acidic. The PH level, in turn, is important for browning: a high PH level facilitates the Maillard reaction, giving you brown and toasty crackers.

Answer 3

Baking soda decomposes when heated (T above 80 °C) releasing carbon dioxide and water. While other answers cover true or untrue aspects, baking soda and other chemical leavures formulation work even without acid/base reactions and without letting the dough stands for raising.

I would say that in addition to the raising due to the starter, your crackers should get an extra raised texture, with inner bubbles typical of less compact crackers, those looking a bit layered, less dense. This last raising would happen while baking.

https://www.scientificamerican.com/article/vanishing-baking-soda/