Medium-temperature daqu

What it is

Medium-temperature daqu is a formed grain starter used in baijiu production. It is a brick containing a mixed community selected during open solid-state fermentation. The brick supplies microorganisms and enzymes to the later grain fermentation and contributes flavor compounds. It is not a named species, an isolate, a commercial pure culture or the distilled spirit.

Sources classify daqu by the maximum temperature reached inside the fermenting bricks. A 2017 study gives the medium-temperature band as 50 to 60 °C. The studied Luzhou Laojiao batch rose from 29.1 °C to a measured core average of 53.4 °C by day 4, stayed between 53.4 and 56.2 °C through day 12, and then cooled. That batch curve is one measured industrial process. It is not a universal preset, and it is not a home temperature target.

Where it is made and studied

The studies document particular production in Luzhou, Sichuan, sampled in January 2013 and September 2016; in Yibin, Sichuan, from a May 2022 production batch; and at a Songhe Co. facility in Henan, where a summer batch was made. A 2020 Henan study sampled a strong-flavor daqu process at several stages. These are modern examples, not an exclusive origin or a single national method.

The sampling dates describe the studied batches. They do not establish a universal manufacturing season.

Ingredients and making

The ASM introduction lists wheat, barley, peas and sorghum among the materials used in daqu making generally. The 2024 Yibin study identifies its substrate as wheat, and the Songhe study describes a wheat or wheat-mixture brick. The sources support cereal-brick construction, but not one fixed formula or cereal ratio for medium-temperature daqu.

During early propagation the Luzhou batch heated itself. Rapid growth over the first four days raised the brick core to about 55 °C. That bioheat was associated with a succession in which several thermotolerant taxa persisted and others declined. Bacterial groups in that sample included Weissella, Leuconostoc, Lactobacillus and later Bacillus. Fungal groups included Thermoascus, Candida, Wickerhamomyces and later Thermomyces. These are time-specific observations from one batch, not an inoculation list.

Role in strong-flavor baijiu

Medium-temperature daqu is used as a saccharifying and fermenting starter in strong-flavor baijiu. The later solid-state fermentation of the grain mash, distillation and the finished spirit are separate stages. The Luzhou study reports that daqu also contributes enzymes and flavor-related metabolites that may be transformed later in brewing. The Songhe study associates mature daqu with volatile aroma compounds, including pyrazines and alcohols. These findings describe the studied systems and do not quantify a universal flavour contribution.

Spatial variation within the brick

The 2022 Songhe study found different communities and physicochemical measurements in the outer and inner layers of the brick. It cultured and identified isolates as well as analysing sequence-based communities; those methods answer different questions, and neither makes a named isolate a suitable commercial or home culture. The 2024 Yibin study likewise reports spatial and temporal variation across the surface, middle and core. The research does not reduce this mixed system to one organism or one mechanism.

Storage, handling and safety

No complete home recipe or validated home-production process for medium-temperature daqu was found. The studies do not give ingredient quantities for a home batch, validated endpoints, a sanitation plan, a stock-retention method or food-specific safety controls. The studied batches ran for about 30 days, and the Songhe study sampled up to four months of storage, reporting relative stabilization in some indices after three months. These are distinct study batches, not a shared schedule.

Sample refrigeration or freezing in the research methods concerns laboratory analysis, not viable starter storage. A species detected in a brick is not automatically a suitable inoculum, and smell, taste, visible growth or a home thermometer reading cannot establish that a brick is safe to use.

Open questions

The earliest attestation of the temperature-defined class is not established. A producer-specific process specification, food-specific safety evidence and retained-stock guidance are not in the inspected material. The class must be kept apart from low-temperature and high-temperature daqu, which are related categories and not interchangeable.