Sodastream for instant carbonation. I've mostly used it for straight club soda with a splash of lime juice, but with this last batch of ginger ale, I thought I'd carbonate a bottle with the Sodastream to compare to the fermented brew. I used Safale S-04, which the company's website calls "A well known English ale strain noted for its fast fermentation and rapid settling." It left quite a lot of sediment, which the carbonation instantly stirs up when I open a bottle. It's also really heavy on the diacetyl, which runs over the rest of the flavors in the fermented ginger ale. I've previously used champagne yeast in a number of batches, which, as you'd expect, doesn't give a butterish diacetyl flavor. I think I used Safale S-05 in my one birch beer experiment, and in that context, I liked a bit of butteriness. Fermentis, though, says that their S-05 has "low diacetyl and a very crisp end palate" which sounds better, at least for ginger ale. The fermented ginger ale is also pretty dry, which I like, but might not seem sweet enough for most people's expectation of soda.
The Sodastream-carbonated version is sweeter, with no sugar turning into alcohol. It's much more floral, especially to the nose. The cardamom, juniper, and especially yarrow make it flavorful, even though the ginger isn't very spicy. Pretty nice, though I might add a bit of lemon juice, not just dry lemon zest, to both versions. Because of the particular yeast, the fermented ale is, well, a bit too aley. So I think the Sodastream wins this round. Next time, I'll have to compare it to a champagne yeast or the S-05, and see if the crisper flavor wins out.