Soy sauce production using the press method involves extracting the liquid soy sauce from a fermented mixture through pressure. Here's how it works:
The Koji Stage: Preparing for Pressing
Before pressing, the soy sauce mixture must reach the koji stage. This involves several key steps:
- Steaming Soybeans: Soybeans are steamed until cooked.
- Roasting and Crushing Wheat: Wheat is roasted and then crushed into smaller pieces.
- Adding Aspergillus Mold (Koji-kin): The steamed soybeans and crushed wheat are mixed with Aspergillus mold spores (typically Aspergillus oryzae or Aspergillus sojae). This mixture is called koji.
- Koji Fermentation: The koji is placed on wooden trays or in controlled environments and allowed to ferment for 2-3 days. This process generates enzymes that break down the soybeans and wheat.
Moromi Fermentation: Developing Flavor
The koji is then mixed with salt water (brine) to create moromi, the fermentation mash. This mixture undergoes a long fermentation period, typically ranging from several months to over a year. During this time, bacteria and yeast work together to develop the characteristic flavor and aroma of soy sauce.
Pressing: Extracting the Soy Sauce
Once the moromi has matured, it's time to separate the liquid soy sauce from the solid residue. This is achieved through pressing:
- Wrapping the Moromi: The moromi is typically placed in cloth-lined containers or bags.
- Applying Pressure: The containers are then placed in a pressing machine. Hydraulic or mechanical pressure is applied to squeeze the liquid soy sauce out of the moromi.
- Collecting the Raw Soy Sauce: The extracted liquid, known as raw soy sauce, is collected.
Post-Pressing Processes: Refinement and Bottling
After pressing, the raw soy sauce undergoes further processing:
- Pasteurization: The raw soy sauce is heated to kill any remaining microorganisms and stabilize the flavor.
- Filtration: The soy sauce is filtered to remove any remaining solid particles, resulting in a clear liquid.
- Bottling: Finally, the soy sauce is bottled and ready for distribution.
The solid residue left after pressing is often used as animal feed or fertilizer.
