In China, due to various reasons, the main problem in the harvest of grape raw materials is usually insufficient maturity, that is, the acid content is too high and the sugar content is too low.
In order to increase the sugar content of the raw materials and make the wine reach the required degree of wine, the method of adding crystalline white sugar is often used. However, care must be taken when adding sugar:
转化率： 17 ～ 18g/L 糖可转化 1% （体积分数）的酒精； (1) Conversion rate: 17 ～ 18g / L sugar can convert 1% (volume fraction) alcohol;
添加时间：应在酒精发酵刚刚开始时加入，并应使所添加的糖充分溶解，与葡萄汁混合均匀。 (2) Adding time: It should be added just before the alcohol fermentation, and the added sugar should be fully dissolved and mixed with the grape juice evenly.
Reverse osmosis and selective freeze extraction can also increase the sugar content of raw materials, but require corresponding equipment investment. Where natural conditions permit, delayed harvesting, natural freezing, and drying treatments are also good ways to improve the quality of raw materials.
There are two main methods to reduce acid content, namely biological acid reduction and chemical acid reduction. - 乳酸发酵主要用于干红葡萄酒；一些降酸酵母菌株可在酒精发酵的同时分解部分苹果酸；而裂殖酵母在白葡萄酒酿造中的应用正在研究中，并取得了令人鼓舞的结果。 In the biological acid reduction method, malic acid - lactic acid fermentation is mainly used for dry red wine; some acid-reducing yeast strains can decompose part of malic acid while alcohol fermentation; and the application of fission yeast in white wine fermentation is being studied. And achieved encouraging results. The only acid-reducing agents used in the chemical acid-reducing method are calcium carbonate, potassium bicarbonate, and potassium tartrate. Need to pay attention when using:
降酸率：要降低 1g/L 总酸（用 H 2 SO 4 表示 ），需添加 1g/L 碳酸钙或 2g/L 碳酸氢钾或 2.5 ～ 3.0g/L 酒石酸钾。 (1) Acid reduction rate: To reduce 1g / L total acid (expressed as H 2 SO 4 ), it is necessary to add 1g / L calcium carbonate or 2g / L potassium bicarbonate or 2.5 to 3.0g / L potassium tartrate.
添加时间：在发酵前降酸，并且使碳酸钙充分溶解，与葡萄汁混合均匀。 (2) Add time: reduce the acid before fermentation, and make calcium carbonate fully dissolved, and mix with grape juice evenly.
For grape juice with a high acid content, the double salt method can reduce the acidity and achieve good results.
For moldy grape raw materials, it is best to make wine by hot dipping or flash evaporation.