Using Liquid Foam from Lentils to make Mediterranean Sourdough

Hi, 

the process of making a sourdough starter with chickpeas is shown here, starting from 2:50. 

It starts with raw chickpeas, and warm water. The master-baker pounds dry raw chickpeas in mortar with pestle to break them down in halves, pours warm water which resulted from boiling water with a bit of cumin and sugar on top of chickpeas/ Water should be warm to touch, not too hot, about 40C. Then he places the jar in a warm place to keep it at around 30-40C throughout the day/night. In this case 'warm place' is jar being surrounded with wood shavings and chips, they work like an insulating blanket around the jar.

When the foam comes out of the jar, long enough "tube" of foam, as shown in the video at 4:27, it's ready to make a sourdough starter with it. 

He blends this foam and liquid drained from fermenting chickpeas with flour and lets the resulting piece of sourdough rise. After that he uses that piece of sourdough to inoculate the bread dough, as a piece of any regular sourdough or levain would. 

So, the answer to your question is no. The foam from cooking peas or lentils, or meat or beans or potatoes, or any other food will not give your sourdough. It must be raw grain, or raw chickpeas, because bacteria and yeast live on the surface of the raw grain and the rising foam is actually a layer of baker's yeast, just like yeast foam on top of fermenting beer. 

At home you can use a simpler process if you have a place where to keep your starter at 40C. LIke in a yogurt maker or inside your oven set to PROOF setting. You obviously don't need outdoors or warm weather for that. 

Soak your whole raw chikpeas in room temp water for 10hrs. 100g chickpeas, 400g water, 20-25C. 

Blend them in a blender  or in a jar with an immersion blender fairly smoothly to break down the grain

It will look like a watery grainy mass, like so:

Add 1 tbsp of sugar, blend and let it sit, uncovered, for 6hrs at 40C. The foam will rise. 

Add to that 1 tsp of salt and 100g bread flour. Mix and let it rise for 8 hrs at warm room temperature (25-30C). Your sourdough starter is now ready to be used in breadmaking.