Verb (type 1): To shake.
Ravistaa appears in our example (from the label of a mustard bottle) in its present passive participle form, ravistettava. In this form it means ”is to be shaken” or ”shakeable.” (See ravistaa conjugated here.)
Ravistettava is often seen in the phrase ”ravistettava ennen käyttöä” (”to be shaken before use”) and appears on many kitchen products and household sprays.
Ravistettava is constructed by removing the –iin ending from the past passive form of the verb (in this case, ravistettiin) and adding the suffix -ava. (-ävä would be the front vowel suffix equivalent).
Wikipedia has a nice article explaining the construction, use and translation of the present passive participle in Finnish here.