I've done a few sahti's. I haven't dialed it in yet, but anything I've done hasn't shown up much in my beers. I harvested some branches and used 2oz in the strike water. I boiled it for 20 min, added it to the MT, then brought to strike temp and mashed in with the branches still in. I've seen mentionings of using branches with green berries instead of blue. I've only used branches with blue ones, so I could see some merit to that claim. If you want to get some more info, then check out Lars' blog at
Exploring the Past, Present, and Future of Nordic Beer - Brewing Nordic.
This is an awesome resource for tye Scandinavian farmhouses that everyone has been mentioning.
However, if that's not where you're interest lies, try making and using your own extract. So, take a small Mason jar and add a few juniper berries. Then grab a bottle of vodka, take a shot, then add a couple shots to the Mason jar. Let it sit for a few weeks.
When both the extract and your beer is ready, grab a few glasses and fill them, making sure they are all even. Also make sure you don't have to drive the rest of the night, and have someone else taste with you. Take a dropper and add a few drops to the first glass, a little more to the next, etc. Once you get to the dosage you find just right and have your helper taste it to confirm, in case your palate is fatigued. Calculate that dosage to your batch size and dial it back 10%. Add a little at a time as needed.
BTW, I think it would work in IPA and witbier. You'd just have to tinker with it and the hop selections.