I wish I could help you, but that style is not familiar to me.
Upon further research in Brewing Techniques
and The Finnish Society for Traditional Beers
, it appears that my ignorance should not be entirely unexpected. I do not know how "traditional" the version you had was, but the style is apparently very old and quite rustic - including wooden mash tuns, open fermentation, bouquets of juniper twigs and finnish baker's yeast. I'm pleased (but not surprised) that you enjoyed the Goose Island version;
that brewery is wonderful, but I strongly suspect that they dramatically modernized the procedures.
At any rate, Sahti seems to be rare, even in Finland. There is another interesting article from Michael Jackson
In what ways did the beer you enjoyed differ from similar Belgian or Flemish rustic ales, or from Weinheinstephaner-types? I'd assume that the replacement of hop profile with juniper is the defining characteristic, although the reviews suggest that the Goose Island version expresses Rye pretty profoundly.
Honestly, your best bet might be to brew it yourself
I discovered a mention that Lammin Sahti Oy
produces a bottled version, but the possibility seems rather remote, and they do not offer an english version website.
I deeply appreciate you providing me the nudge to learn!
My dear wife gave me several interesting beers for Christmas, and I will try to report on them in due course.