Old English sur "sour, tart, acid, fermented," from Proto-Germanic *sura- "sour" (source also of Old Norse surr, Middle Dutch suur, Dutch zuur, Old High German sur, German sauer), from PIE root *suro- "sour, salty, bitter" (source also of Old Church Slavonic syru, Russian syroi "moist, raw;" Lithuanian sūras "salty," sūris "cheese").
Meaning "having a peevish disposition" is from early 13c. Sense in whisky sour (1885) is "with lemon added" (1862). Sour cream is attested from 1855. French sur "sour, tart" (12c.) is a Germanic loan-word.
"a favorite German dish consisting of cabbage cut fine, pressed, salted, and fermented until sour," 1630s, from German Sauerkraut, literally "sour cabbage," from sauer "sour" (from Proto-Germanic *sura-; see sour (adj.)) + Kraut "vegetable, cabbage," from Old High German krut, from Proto-Germanic *kruthan.
They pickle it [cabbage] up in all high Germany, with salt and barberies, and so keepe it all the yeere, being commonly the first dish you have served in at table, which they call their sawerkrant. [James Hart, "Klinike, or the diet of the diseased," 1633]
In U.S. slang, figurative use for "a German" dates from 1858 (compare kraut). "The effort to substitute liberty-cabbage for sauerkraut, made by professional patriots in 1918, was a complete failure." [Mencken]. French choucroute (19c.) is the German word, but via Alsatian German surkrut but with folk etymology alteration in French based on chou "cabbage" + croûte "crust" (n.).