There are as many ways to brew sahti as there are sahti brewers.
In general eastern areas (Joutsa) brew paler sahti (they use
wheat) than other areas.
Also the ingredients vary wildly.
You could say that you can put any malts to the mash though
pilsner malt, rye and wheat are most common. You can use hops
or then again not. You can use juniper but many traditional
sahti brewers don't.
There are some things you do. You use baking yeast (though
some blend of german weizen yeast or belgian strong ale
yeast might do well). There are lots of phenolic and banana
flavours in sahti and I mean lots.
In the brewing process there are some peculiarities. Most
of the brewers don't boil the wort. Instead they might boil
the mash for a short time. You want to have long chained
proteins in sahti to give it some cloudiness and viscosity.
And who cares about breaks, all that fluffy stuff will sediment
in the bottom of fermentation vessel anyway. Sahti will be consumed
so quickly that there are no need to be worried about
Well, to be serious I have collected some real recipes
to follow. Especially the text by Simo Juvaste is worth
Note! Traditional sahti got a certificate of
specific character for agricultural products and foodstuffs
in EU-area on February 8th 2002. You can read how the
application describes the traditional process and ingredients.
Sahti malt specification
Brewing Finnish Sahti by Simo Juvaste
Sahti recipe by Kari Likovuori
Sahti by Jukka Heino
Brewing sahti in Kuhmoinen