But testing a January iced espresso tonic with 18 g rosemary-orange syrup, 120 g tonic, and a double over ice, topped with salted cold foam, but the foam falls flat in about 3 minutes under 16 oz lids. Anyone keeping aromatic foams stable in service — do you prefer 0.5% xanthan, switching to oat for protein, or an iSi whip (1 N2O per 500 ml) to keep structure without a gummy finish?
Had the same issue — what helped was dissolving xanthan into the syrup at 0.15–0.2% and foaming skim milk, then iSi with 2 N2O per 500 ml and a 2‑minute rest; held about 6–7 minutes under 16 oz lids. Go higher than 0.2% and it turns slick, and oat collapsed faster for us. “Tonic is a foam bulldozer,” so keep the syrup, milk, and canister fridge-cold before building.
And i’ve had some luck using a bit of soy milk instead of oat — it holds structure pretty well, and you might find it retains the flavor better too. Just be sure to use an iSi whip at 1 N2O per 500 ml for optimal stability. Have you tried that yet?