Study On Key Technology Of Cold Brew Coffee Production

Coffee is a beverage made from roasted and ground coffee beans.It is one of the three major drinks in the world.At present,coffee has become one of consumers’ favorite drinks,especially ready-to-drink coffee,which is popular for its convenient and fast drinking.Cold brew coffee is made by steeping ground coffee beans for more than 12 hours in water at room temperature or lower,using a professional filter.Cold brew coffee is characterized by low acidity and bitterness,more genuine taste and aroma,and a long drinking period.As a new coffee product,cold brew coffee occupies an advantage in the American coffee market.However,cold brew coffee products are not widely used in China’s consumer market at present.Polysaccharide and its degradation products in coffee contribute significantly to the viscosity,taste and pure thickness of coffee and help to retain volatile aroma components.The solubility of polysaccharide is greatly affected by temperature so that which is one of the key differentiating components in cold brew coffee.In this study,the effects of roasting degree,grinding degree and ratio of material to water on physical and chemical properties,color,polysaccharide content and molecular composition,sensory quality of cold brew coffee were determined,and the optimal technological parameters of cold brew coffee were determined.At the same time,the quality differences of cold brew and hot brew coffee were compared,including the differences of basic physical and chemical indexes,polysaccharide content and molecular composition,sensory quality,etc.The main results are as follows:（1）Three cold brew coffees prepared from Arabica coffee beans with light,medium and deep roasted and it was found that the total sugar content,reducing sugar and viscosity decreased with the increase of roasting degree,while the contents of total acid and total phenol and the bitterness increased with the increase of roasting degree.Arabinogalactan and galactomannan were the main polysaccharides in Arabica coffee beans with three baking degrees.The content of arabinogalactan decreased gradually with the increase of baking degree,and the content of galactomannan increased gradually with the increase of baking degree.The molecular weight of polysaccharides in light,medium and deep roasting coffee beans were in 3096～15125 Da,2808～13967 Da and 1983～7478 Da,respectively,that is the molecular weight distribution of polysaccharides decreased with the increase of roasting degree.Cold brew coffee prepaped from medium-roasted Arabica coffee beans had the best taste and highest sensory score.（2）Different cold brew coffee were prepared with medium-roasted Arabica coffee beans and which were firstly grinded with gear spacing of 0.30 cm,0.35 cm,0.40 cm,0.45 cm and 0.50 cm respectively.It was found that the total sugar content,reducing sugar content and viscosity decreased with the decrease of comminution degree.The lowest total acid content was 3.78 g/L when the gear spacing was 0.40 cm.The best taste and sensory score were obtained when the gear spacing was 0.40 cm.（3）The cold brew coffee prepared by grinding moderately roasted coffee beans at a gear spacing of 0.40 cm under the conditions of material-water ratio of 1:10,1:11,1:12,1:13 and 1:14,respectively,found that the total sugar content,reducing sugar content and viscosity first increased and then decreased with the increase of material-water ratio,and reached the maximum at 1:12,when the total sugar content was The total acid content gradually decreases with the increase of the material-water ratio,with the total acid content of 5.62 g/L at 1:12 and the lowest content of 0.25 g/L at 1:12.When the material-water ratio is 1:12,the cold brew coffee has the best taste and the highest sensory score.（4）Moderate baking,grinding with gear spacing of 0.40 cm,cold brew and hot brew coffee were prepared under the condition of material-water ratio of 1:12,and the basic physical and chemical indexes of coffee under the two brew methods were measured.It was found that the contents of soluble solids,the total sugar content,total acid and total phenol in hot brew coffee liquor were higher than those in cold brew coffee liquor by 1.32%,0.85%,0.26%and 0.30%respectively.Sensory evaluation of cold brew coffee is lower in bitterness and sourness,more harmonious in taste,and its sensory score is better than that of hot brew coffee.The main polysaccharides in cold brew and hot brew coffee are arabinogalactan and galactomannan,and the content and total polysaccharide of hot brew coffee are higher than those of cold brew coffee.The polysaccharide content of cold brew coffee is higher than that of hot brew coffee at 50%,50%～67%and 67%～75%alcohol precipitation concentration,and the polysaccharide content of hot brew coffee is higher than that of cold brew coffee at 75%～80%.The molecular weight of the cold brew coffee polysaccharide is 2256～12305 Da,and that of hot brew coffee polysaccharide is 2947～9497 Da.The infrared spectra of polysaccharides extracted by two methods show that the absorption peaks of polysaccharide components precipitated by 50%～67%and 67%～75%alcohol are different around 914.09～763.60 cm-1.