It is produced through a natural process – fermentation, then followed by neutralization and crystallization process.

Here are 4 authority resources mentioned the manufacturing process, respectively from Wikipedia, EFSA, a China big manufacturer and Ajinomoto.

Let’s see one by one.

1. Wikipedia
Generally, MSG is now industrially produced by the fermentation of starch and sugar, such as corn starch and tapioca starch instead of extracting and crystallizing from seaweed by a Japanese scientist in 1908 when it was first made. (1)

2. EFSA
There are two bacterial approved for the fermentation of L-glutamic acid, one is corynebacterium glutamicum from strain 2256; another is a new one, from the genetically modified strain of C. glutamicum (i.e. strain EA-12).

In both processes, glutamic acid is produced by fed-batch fermentation using carbon sources of vegetal origin (sucrose), nitrogen sources, salts and vitamins.  (2)

3. A China Big Manufacturer
Starting from the fermentation of glucose, using corynebacterium glutamicum to produce glutamic acid then neutralize with sodium carbonate. The subsequent steps are decolorization, filtration, crystallization, centrifuge, drying and so on.

4. Ajinomoto
Ajinomoto said their brand MSG AJI-NO-MOTO® produced in Brazil is through the fermentation of sugarcane molasses and here with the detailed flow chart. (3)

msg manufacturing process

Specification
Structure
msg chemical structure
Image Source

Other names   
Monosodium L-glutamate
L-glutamic acid, sodium salt
Appearance    A white, practically odorless crystalline granular or powder.
CAS number    6106-04-03 (monohydrate)
Chemical formula    C5H8NaNO4.H2O
Molecular weight    187.13
Melting Point    232 °C (450 °F; 505 K)
Solubility   
Freely soluble in water with the solubility 740 g/L in water. It dissociates into glutamate and sodium ions.
Practically insoluble in ethanol or ether.
Stability    Stable in high temperatures and in the presence of light. Around 0.6% of MSG will decompose when heated its 10% solution in 100ºC for 3 hours in PH 6.9. It will lose the combined crystallization water when heated to 120ºC.