Mago gives the following instructions for excellent passum. Harvest well-ripened very early bunches of grapes; reject any mildewed or damaged grapes. Fix in the ground forked branches or stakes not over four feet apart, linking them with poles. Lay reeds across them and spread the grapes on these in the sun, covering them at night to keep dew off. When they have dried, pick the grapes, put them in a fermenting vat or jar and add the best possible must (grape juice) so that they are just covered. When the grapes have absorbed it all and have swelled in six days, put them in a basket, press them and collect the passum. Next, tread the pressed grapes, adding very fresh must made from other grapes that have been sun-dried for three days. Mix all this and put the mixed mass through the press. Put this passum secundarium into sealed vessels immediately so that it will not become too austerum. After twenty or thirty days, when fermentation has ceased, rack into other vessels, seal the lids with gypsum and cover them with skins.