"This beef is too salty."
Noun + 是 + Noun
Noun + 很 + Adjective
This is a "noun + adjective" sentence so there is no need for 是。Also remember that 很 gets replaced when the adjective is negated (不) or uses other intensifiers (太, 真, 非常, 最, etc).
他是老师 = He is the teacher
他很高 = He is tall.
这个牛肉很咸 = This beef is salty.
这个牛肉不咸 = This beef is not salty.
这个牛肉太咸了 = This beef is too salty.
It is possible to use 是 when an adjective is changed into a noun with 的 for emphasis.
我狗很大- My dog is big.
我狗是大的 - My dog is the big one.
这个牛肉是咸的 - This beef is a salty one.
You would probably only say it that way for emphasis or comparison, but it wouldn't be the same meaning as "too salty" with 太...了.