Quelle

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Grabek-Lejko D. et al., The bioactive and mineral compounds in birch sap collected in different parts of habiatats, „Baltic Forestry” 2017, 23(1), 394–401.
Hamilton A., Birch Sap Wine and how to tap a birch, theotherandyhamilton.com/2012/03/17/birch-sap-wine/, (24.07.2018).