A method for determining the quality of a juice or cider comprising: isolating DNA from said juice or cider according to an improved method for isolating nucleic acids from a liquid, the method comprising: separating the solid components from the liquid soluble components in said liquid; lysing the cells present in said solid component to release nucleic acids, polysaccharides, lipids, and proteins; generating an organic phase, an interface, and an aqueous phase wherein said lipids are in said organic phase; wherein said proteins are in said interface; and wherein said nucleic acids and polysaccharides are in said aqueous phase; separating said aqueous phase from said organic phase and said interface; and separating said nucleic acids in said aqueous phase from said polysaccharides in said aqueous phase by mixing an aqueous solution of cetyl trimethyl ammonium bromide (CTAB) and salt with said polysaccharides and said nucleic acids, wherein said nucleic acids precipitate out of said aqueous solution, and wherein said polysaccharides remain dissolved in said aqueous solution; and separating said aqueous solution from said nucleic acids; exposing said DNA obtained from said juice or cider to a first primer, a second primer, and to a fluorescent composition, wherein the sequence of said first primer and the sequence of said second primer are complementary to specific sequences in a DNA of the microorganism Candidatus Liberibacter asiaticus (CLas) and bind to said specific sequences in said microorganism's DNA, and wherein the sequence of said first primer comprises SEQ ID NO: 1, wherein the sequence of said second primer comprises SEQ ID NO: 2; amplifying said DNA to generate an amplicon; determining the Ct value of said amplified DNA; and wherein when said Ct value of said amplified DNA is approximately 30 or less said juice or cider has poor quality. separating the solid components from the liquid soluble components in said liquid; lysing the cells present in said solid component to release nucleic acids, polysaccharides, lipids, and proteins; generating an organic phase, an interface, and an aqueous phase wherein said lipids are in said organic phase; wherein said proteins are in said interface; and wherein said nucleic acids and polysaccharides are in said aqueous phase; separating said aqueous phase from said organic phase and said interface; and separating said nucleic acids in said aqueous phase from said polysaccharides in said aqueous phase by mixing an aqueous solution of cetyl trimethyl ammonium bromide (CTAB) and salt with said polysaccharides and said nucleic acids, wherein said nucleic acids precipitate out of said aqueous solution, and wherein said polysaccharides remain dissolved in said aqueous solution; and separating said aqueous solution from said nucleic acids; exposing said DNA obtained from said juice or cider to a first primer, a second primer, and to a fluorescent composition, wherein the sequence of said first primer and the sequence of said second primer are complementary to specific sequences in a DNA of the microorganism Candidatus Liberibacter asiaticus (CLas) and bind to said specific sequences in said microorganism's DNA, and wherein the sequence of said first primer comprises SEQ ID NO: 1, wherein the sequence of said second primer comprises SEQ ID NO: 2; amplifying said DNA to generate an amplicon; determining the Ct value of said amplified DNA; and wherein when said Ct value of said amplified DNA is approximately 30 or less said juice or cider has poor quality.