Clean the fresh tomatoes and cut to pieces.Put then into the flask and place in a 4℃ refrigerator for 8~12h,then strain through gauze.Suspend 60 g of base medium in 950 ml of distilled or deionized water,add 50 ml of tomato juice.Heat with frequent agitation and boil to completely dissolve the powder.Adjust the pH and then distribute into flasks.Autoclave at 121℃ for 15 minutes.