Vinification of Madeira Wine Blandys 10 Years Sercial: fermented with natural yeasts at a temperature of 18 to 21ºC in temperature-controlled stainless steel vats. Approx. After 5 days, fortification is carried out with wine alcohol (96% v/v), in order to maintain the desired natural sugar content. Aging: Blandy`s Sercial 10 years old is aged for 10 years in American oak casks according to the traditional ‘Canteiro process.