Why a Batch of Black Sesame Paste Tested 27× the Mold Limit

In its latest round of food-safety sampling, the Shanghai Municipal Market Supervision Administration flagged a batch of "Weiwei" (维维) unsweetened black sesame paste produced on August 13, 2025 (320 g per bag). All five samples from the batch failed the mold test, with the highest reading reaching 2,800 CFU/g — 27 times the national limit of 100 CFU/g set by GB 19640-2016 for reconstituted cereal products. When asked, the company's customer service confirmed that the entire affected batch had already been recalled.

Behind the headline numbers is a story worth telling from the ground up — what mold actually is, why a bag of powder is such an easy target, and what a "27× over limit" reading really means. Let's take a closer look.

What Is Mold, Exactly?

Mold is the everyday name for a large group of filamentous fungi — the same kingdom of life that includes mushrooms and yeast. A mold colony is built from hyphae: long, branching threads that weave together into a visible network called mycelium, the fuzzy growth you see on spoiled food. What you usually notice first, though, are the spores — tiny reproductive bodies, often just a few micrometers across, that form at the tips of stalks. They float in the air almost everywhere; given moisture, warmth, and food, a single spore can germinate and grow into a whole new colony.

Because spores are so small and so abundant, mold is something you rarely see in detail with the naked eye. Under a microscope, however, the structure is beautiful: radiating hyphae, spherical spore heads, and branching networks that look like miniature forests.

Why Powdered Foods Are a Mold's Paradise

Not all foods are equally vulnerable — and powdered mixes like black sesame paste are about as vulnerable as it gets, for three reasons:

- Abundant nutrition. They are packed with starch and sugars, an ideal carbon source for fungal growth.

- Huge surface area. A powder exposes far more surface per gram than a solid piece of food, giving spores more landing and germination sites.

- Moisture attraction. Powders readily absorb humidity from the air. Once the surface moisture crosses a threshold (what food scientists call water activity), spores germinate quickly — and clumps inside a bag can create tiny damp micro-zones that keep the colony thriving.

That is why regulators treat mold as one of the core hygiene indicators for reconstituted cereal products: if a batch shows heavy mold growth, something in the process allowed moisture and contamination to meet.

What "27× the Limit" Actually Means

The unit CFU/g stands for colony-forming units per gram — a count of how many viable mold colonies can be cultured from each gram of the product. The legal limit of 100 CFU/g already assumes some background exposure is unavoidable in food. A reading of 2,800 CFU/g means the sample carried 28 times more culturable mold than the standard tolerates — not a minor blemish, but evidence of serious spoilage.

The detail that matters most is that all five samples from the batch exceeded the limit. Random, one-off contamination rarely hits every sample at once; when an entire batch fails, it points to a systemic breakdown somewhere in production, storage, or transport rather than an unlucky accident.

Why Mold Is the Core Indicator of Food Hygiene

Mold is a warning flag for two distinct kinds of risk:

- The mold itself. Ingesting heavily spoiled food can cause acute gastrointestinal illness — abdominal pain, diarrhea, and vomiting — and mold spores are also common allergens and respiratory irritants.

- The toxins it leaves behind. Far more dangerous are the mycotoxins some molds produce as metabolic byproducts, such as aflatoxins. Mycotoxins are largely heat-stable, so ordinary cooking does not destroy them, and chronic low-level exposure is associated with damage to the liver and kidneys. Health experts quoted in the report warn that long-term intake of mycotoxin-contaminated food can steadily harm these organs.

In short, mold is not just "something growing on the food" — it is a proxy for whether the whole chain, from raw material to your bowl, stayed clean and dry.

Where Did the Chain Go Wrong?

Reports point to a familiar set of suspects for powdered foods:

- raw ingredients exposed to moisture during storage;

- inadequate disinfection in the production workshop;

- defects in packaging seals that let humidity back in; and

- poor temperature and humidity control during warehousing and transport.

Any single one of these links can introduce spores or give them the moisture they need. For a product as moisture-sensitive as a powdered mix, the chain is only as strong as its weakest link.

The Lesson Beyond One Brand

The same bulletin tested 1,870 batches across 17 food categories and found only 7 non-compliant — a pass rate above 99%. Most producers do it right most of the time; the failures that slip through are the ones that teach the industry where vigilance must live: at the factory floor, not just in the boardroom.

The brand involved is a household name from the 1990s ("维维豆奶，欢乐开怀"), which has recently returned to its core business under a state-owned controlling shareholder. Governance reform, however, does not automatically upgrade the hygiene controls on a production line. As one economist put it, the lifeblood of a food company lies in frontline production management — and a single serious food-safety incident can erode decades of brand trust.

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References:

[1] Shanghai Municipal Market Supervision Administration, Food Safety Sampling Bulletin No. 25, 2026.

[2] GB 19640-2016, National Food Safety Standard for Reconstituted Cereal Products (冲调谷物制品).