it is much too salty

[park sang joon]

1) Babies under a year old should not be given cow's milk because it is much too salty for them, nutritionists have warned.
<Source: Cow's milk 'too salty for babies' of Health In The Telegraph http://www.telegraph.co.uk/health/healthnews/8674967/Cows-milk-too-salty-for-babies.html>

I have known 'much' modify a verb, the comparative form of an adjective or adverb, the superlative form of an adjective or adverb, and a past participle.
But in #1, 'much' modifies the adverb 'too' and I'd like to know how this is possible.

Thank you in advance for your help.

 

[AutumnOwl]

I found this explanation:

All expressions which modify comparative adjectives and adverbs can be used to modify too. Examples are: much, a lot, far, a little, a bit, rather
Read more at http://www.englishpractice.com/words/too-and-too-much/#IbI5cB710VqzWESP.99

 

[park sang joon]

Thank you, AutumnOwl, for your So Very helpful answer.
I do really appreciate your very valuable answer.