Well I am being unnecessarily harsh. Both are listed by the OED, with "offen" being listed first. Our pronunciation in Britain has historically preferred contraction, a preference that appears to be waning, possibly due to the effects of

In my kind of talk, in the sense you mention, ... clearly, a schwa replaces the vowel. "I k'n gowith you". Do you have the "pin"/"pen" merger? (If so, where are you from?) If youdo, your "kin"