Normally, sahti is not bottled to bottles that can keep the pressure and that's why sahti has quite low CO2 content. For making sahti you need normal equipment for making full mash beer. Here is a recipe for making a small patch. Adding hops to sahti is not necessary. Many traditional recipes don't include hops.
Procedure Put all barley and rye malt to a big kettle.
Add 1.5 litres of water of temperature about 40 degrees centigrade. Add another 1.5 litres of water every half an hour. Stir the mash when you add more water. Every time, the added water should be warmer than previously added. The last 1.5 litres should be boiling.