Fortify
/ˈfɔːtɪfaɪ/
verb
To increase the defenses of; to strengthen and secure by military works; to render defensible against an attack by hostile forces.
To impart strength or vigor to.
To add spirits to wine to increase the alcohol content.
“Sherry is made by fortifying wine.”
Synonyms: castellate, incastellate, incastle, secure, strengthen