Naturally occurring MSG in demi-glace?

Yngve_Hilmo_12861

I made 2L pressure-cooked brown pork stock from 2kg ribs & minced meat + mirepoix and a sachet. Roasted the bones in the oven for one hour before pressure cooking for two hours and then strained and skimmed off the fat. Then I reduced the stock to about one tenth. The concentrated reduction had a strong, salty flavour, but I did not add any salt to the stockpot. Does this salty flavour simply come from naturally occurring MSG? And because the liquid was reduced so much, at this point the concentration of MSG is very high and can easily be identified as salty (because MSG is a salt)? 

Latley I´ve been chasing umami/msg, and trying to both incorporate and identify this taste in my cooking, inspired by stuff like these two links; 
http://www.molecularrecipes.com/molecular-gastronomy/umami/
http://www.youtube.com/watch?v=ji74pUeMayg (David Chang talking about MSG)

Tim_Roth_78505

Naturally occurring glutamate from plant or animal tissue is not going to be monosodium glutamate - the sodium salt of glutamate. The umami that you're getting from cooking the stock is the result of releasing free amino acids from protein chains by heating them and causing them to chemically break down - hence why "hydrolyzed vegetable protein" (i.e. broken down vegetable protein) is used to give "umami" taste to processed foods. It's very possible that the salty flavor is just naturally occurring salt that you're only starting to taste because you've reduced the volume of the liquid by 90%, thus increasing the concentration of any sodium ions in the original liquid to 10-times what they were to start with. 

So to clarify: the saltiness here is coming from sodium, and the umami is coming from glutamate, but the sodium and the glutamate were never bonded together as MSG to start and their concentrations in your food will be independent from one another. The saltiness could be coming from the meat, but also the mirepoix (celery has a similar salt content to some raw meats, for example), whereas the glutamate is mostly going to come from just the meat itself.