Source: Simo Juvaste (firstname.lastname@example.org), r.c.b., 5/7/93
Since sahti is traditionally brewed by each household themselves, there is no a single accurate recipe for sahti. Each brewer has his/hers own version, and since the recipe isn't in a written form but as a "awareness of the process", the recipe usually varies more or less between the brews.
Put the malts to one or several big enough but not too deep containers, two 40 liters containers will do well. Add ~5 litres of boiling water, stir well. During next ~6 hours: twice an hour add ~2.5 liters of boiling water and stir. The amount of water and time are approximate. This method will not keep the temperature near the optimal 65-68, but I believe that the time will do the thing. A hot place to mash would probably raise extract rates, though I don't know if it is worth it. Insulating the containers would also help.
I I I I ImmmmmmmmmmmmmmmmmmmmmI ImmmmmmmmmmmmmmmmmmmmmI <- the mash \:::::::::::::::::::/ <- the juniper twigs \- - - - - - - - -/ <- wooden support for the juniper twigs \ / ------||-------
Of course, any filter will do. The 20 kg batch fits well on a 40 cm x 150 cm filter consisting of a layer of juniper twigs. About 3-5 cm layer of junipers is thick enough.
Boil the junipers for a while before laying them to the filter. Put the mash to the juniper filter. Allow to filter, rinse with boiling water to add to the required volume of the wort. 40-50 liters of wort gives fairly good sahti. Allow to filter. Boil the wort for a while. Filter the wort again through the juniper-mash filter, rinse with boiling water.
The wort is ready.
The less water in the wort, the stronger sahti. Also, the first wort to come out of the filter can be used to produce stronger sahti, the rest to produce thinner sahti. The more important party the stronger sahti, the more important drinkers the stronger sahti. A not-so-strong sahti is usually called "naistensahti", women's sahti.
The amount of rye can be varied. E.g. 20 % instead of the above 10 % would give a bit stronger rye taste.
The yeast used can affect on the taste. The Finnish baking yeast is quite effective and it will give quite a sour taste. I don't know how beer yeasts will do. I believe that those would do well. Anyway the sourness is quite characteristic for sahti.
All instructions given above are approximate. I myself would consider it dull to make beer or sahti using same recipe (or any accurate recipe) every time. Perhaps other Finnish readers of this news-group (or HBD) could give some other sahti recipes.
I was also asked about suggestions how to use sauna in brewing. A warm sauna (60-70 C) is an excellent place to mash since it is easy to keep the mash at desired temperature however long you want to. Besides, sauna has been traditionally considered as the cleanest place of a Finnish household.