Reaction of glucose with 2,4-dinitrophenylhydrazine (DNPH)
The test is based on imine formation. The formation of imine from carbonyl compound occurs in equilibrium ergo the principle of Le Chatelier is applicable to the test. According to this principle the increase of the concentration of at least one of the products results in the decrease of degree of conversion of the reactant.
I guess that you are trying to perform the test in aqueous solution, because glucose has poor solubility in ethanol. The second product of the conversion of carbonyl to imine is water. So, performing the reaction in the tremendous excess of water, you are in fact pushing the degree of conversion toward zero in accordance with the principle of Le Chatelier.
That's why the expected precipitate is not formed.