Saturday, July 5, 2014

Classical Gas: a LAB Experiment

A brewer's "blow out tube" system is modified to aid in lacto-fermentation to displace CO2.

Sulfide gas, the devil in the bottle

In a salt rich environment, microbial activity is suspended with exception of lactic acid bacteria (LAB). Once a colony is established LAB creates an acid environment in which it will  synthesize sugar and protein into enzymes and amino acids. But most importantly it creates the glutamic acid responsible for the umani flavor. At room temperatures, carbonic acid forms rapidly as organic matter breaks down. As it degrades into carbon dioxide gas (CO2) and water it gives kimchee and other fermented foods a characteristic complex, tart flavor. CO2 becomes very soluble at lower temperatures, penetrating deeper into fermented food matter taking the umani and other flavors along with it.

The Experiment: Pass the Gas
In a long winded way I’ve described first and second fermentation. Lacto-fermentation occurs in the absence of oxygen as it creates CO2, which is heavier than air. In a closed chamber it displaces air and oxygen creating the essential anaerobic environment. As any brewer knows, CO2 can build up quickly in a sealed vessel, forming pressure that can literally blowing the lid right off... with fragrant results. Airlocks are commonly used to alleviate the pressure, but does little about the infamous odor. Most of the kimchee aroma comes from sulfides in garlic, chives and cabbage. I’m experimenting with a “blow out tube” system commonly used in beer fermentation. But instead of draining overflowing liquid, I intend to filter CO2 and sulfide gases as they dissolves in water to trap the trademark aroma. Gather these materials:
  • a mason jar of prepared kimchee
  • a drill
  • plastic aquarium airline and tube connecters
  • a clean soda bottle
  • rubber bands
As CO2 displaces air, the plastic tube delivers and neutralizes pungent sulfide gas into a water.

Up your nose with a plastic hose.
For this LAB experiment I bought some plastic aquarium airline and tube connectors at a pet store. I modified a connector into a one-way spout by cutting off and sanding one end flat and widened the opening. Drill a clean hole though a mason jar lid, select a bit that matches the barrel of the the connector. Attach the airline tube snugly. Now make sure the cap is screwed on tightly. Lead the other end of the tube into a bottle of water and secure the tube in place with rubber bands.

As CO2 pressure builds, it is forced gas up and through the hose down into the bottle of water. CO2 and sulfide gas molecules easily lose their covalent bond in water and dissolve to form a weak acid; pungent aromas are also filtered and absorbed in water. The idea is to remove enough CO2 to allow a gentle carbonation that will lead other gasses out of the fermentation chamber, while retaining enough CO2 to aid in creating deep, complex flavors. That’s the mechanics of carbon dioxide gas production, so far it works well at room temperature (68-72°F). The water has already absorbed some of the sulfides. When acid levels drop to 4.2 pH I’ll move the set up to refrigerated temperature (38-41°F) for second fermentation. At lower temperatures CO2 will slowly develop deep, complex flavors in kimchee over the course of four to six weeks. Stay tuned!

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