# HS-SPME Combined with GC-MS/O to Analyze the Flavor of Strong Aroma Baijiu _Daqu_
## 1 Introduction  
Baijiu, known as Chinese national liquor, is a part of Chinese traditional culture. As one of the daily alcoholic beverages, it is prevalent among Chinese people [1]. _Qu_, as the source of flavor and microorganism for baijiu, has received wide attention in baijiu production [2, 3]. _Qu_ is a starter, saccharifying agent and aroma generator in baijiu production, and plays a vital role in baijiu making [1]. The main types of _Qu_ are _Daqu_, _Xiaoqu_, and _Fuqu_, and the primary raw materials of _Qu_ are wheat, sorghum, and bran, respectively. The relevant microbes that play a major role in the _Qu_ fermentation including moulds, yeasts, and bacteria [2]. There are 12 flavor types of baijiu, among which Strong, Light, Sauce, and Rice aroma baijiu are four basic flavor types, and other flavor types are derived from the basic flavors [4]. The 12 flavor types of baijiu are closely related to the kinds of _Qu_. According to the main technical characteristics of the 12 flavor types of baijiu and the primary production technology of _Qu_, the relationship between flavor types and _Qu_ is summarized as shown in Figure 1a. Flavor wheel has been often used to help people understand and identify the flavor of a complicated product. The Baijiu flavor wheel [5] describes the sensory characteristics of baijiu from three aspects: aroma, taste, and mouthfeel (Figure S1). The aroma of raw materials, fermentation aroma, and aging aroma are three important aroma components for the Baijiu Flavor Wheel. _Qu_ aroma is one of the seven kinds of aroma to evaluate raw materials aroma. _Daqu_ used in SAB is a kind of _Qu_. Crushed wheat and other raw materials are mixed with an appropriate amount of water to produce _Daqu_, which is thenmade into \(Qu\)-bricks with a specific mold. Then, the \(Qu\)-bricks were transferred to the fermentation room, appropriate straw use for isolation and moisture absorption. Pile the fermented \(Qu\)-bricks in the store room to be crushed for use. The immediate process of \(Dau\)-making is demonstrated in Figure 1b. _Daqu_ contains high protein and is rich in starch and other nutrients, which is the primary source of microorganisms [3]. It can provide microorganisms with hydrolytic enzymes that hydrolyze macromolecules in fermented grains. In the process, an aroma is produced, which we call \(Qu\) aroma. Strong aroma baijiu (SAB) is one of the baijiu flavor types accounting for more than 70% of the market, for which sorghum, rice, sticky rice, wheat, and corn are used as the raw material. Its standard production technology is steamed grains mixed with _Daqu_ are put into _pit (jiacchi)_ for fermentation. After fermentation in the pit, solid-state distillation occurs with _zeng_ (a kind of distillation device). Containers are used to collect and store baijiu. At present, the research on the flavor of SAB is aimed at the study of the overall flavor of baijiu [6], the change rule of flavor substances in the baijiu distillation process [7] and the characteristic aroma: roasted and mud-like aromas [8]. This study is carried out in view of the problem that the research on \(Qu\) aroma is not sufficient. The samples in this experiment are six kinds of _Daqu_ from the freshly pressed _Daqu_ block in the production process to the _Daqu_ before it is officially put into SAB production. At present, there are mainly two methods for the extraction of volatile compounds from solid samples: (1) To make the volatile compounds of the samples reach equilibrium in the headspace in the confined space, and then use the extraction fiber coated with unique materials to extract directly from the headspace gas of the samples; (2) To extract the volatile compounds from the solid to the liquid by using the principle of compound similarity compatibility. Then, the liquid sample was concentrated and extracted by the pretreatment method.