# Ca Thinh Lap Thach – Vinh Phuc’s Fermented Fish That Takes Three Months to Make

> Source: https://foodvietnamese.com/ca-thinh-lap-thach/
> Updated: 2026-08-20

**Ca thinh Lap Thach** (Vietnamese: *cá thính Lập Thạch*, also called *cá muối chua* – sour salted fish) is the signature fermented specialty of Lap Thach district, Vinh Phuc province, northern Vietnam. Fresh freshwater fish are salted for several days, then coated with **thinh** – coarsely pounded roasted corn and soybean – layered with **guava leaves** in a sealed terracotta jar and left to ferment naturally for **3–4 months**. After three to four months of fermentation, the fish becomes firm and pinkish-red, with a subtle sourness and rich, savoury fragrance from the thinh. Grilled over charcoal to serve. In 2010, Vietnam’s National Office of Intellectual Property granted trademark protection to ca thinh Lap Thach for its food-safe production process. Named one of **Vietnam’s Top 100 Specialties 2020–2021**. The first time I encountered ca thinh was at a small market stall in Lap Thach. The vendor had two rows of fish pieces laid out on a tray, each piece coated in a dull golden granular crust. The smell was unlike anything I expected from fermented fish – no sharpness, no pungency. Just the warm, toasted smell of corn and soybean, with a faint sour note underneath. “Grill it at home over charcoal,” she said. “Don’t add anything.” That evening, with nothing but a piece of ca thinh on a charcoal grate and a pot of plain rice, I understood what three months of patience produces.

*— Kelly Thuy*

🐟**Ca thinh Lap Thach grilled over charcoal – golden-brown thinh crust, deep pinkish-red flesh inside**

## What Is Ca Thinh Lap Thach?

Lập Thạch fish fermented in roasted rice powder, locally known as cá thính Lập Thạch, embodies the essence of traditional northern flavour. The name “thinh” refers to any roasted grain or legume ground or pounded for use in fermented food preparation – it appears in several northern Vietnamese specialties, including thit chua (Phu Tho fermented pork) and various regional nem chua (fermented pork roll). The Lap Thach version uses a specific combination of roasted corn and soybean, making it distinct from fish-fermenting traditions in other northern regions that use roasted rice.

**Ca thinh ≠ dried fish ≠ fish sauce:** Ca thinh occupies its own middle ground. Unlike dried fish, the flesh retains moisture and has not been desiccated. Unlike fish sauce or fish paste (mam), the fish retains its shape, texture and individual flavour. The fermentation produces sourness and depth while the thinh crust produces crunch – a combination neither dried fish nor fish sauce achieves. 

| Quick Facts | Details |
| --- | --- |
| Vietnamese name | Cá thính Lập Thạch; also cá muối chua (sour salted fish) |
| English name | Ca Thinh Lap Thach · Vietnamese Fermented Fish in Roasted Grain |
| Location | Van Quan commune, Lap Thach district, Vinh Phuc province |
| Best fish for this dish | Snakehead (ca qua/ca lo); also carp, roach, grass carp, tilapia |
| Thinh composition | Roasted corn + roasted soybean, pounded to coarse granules |
| Key layering ingredient | Fresh guava leaves (medium-aged) |
| Fermenting vessel | Terracotta jar (lo sanh), sealed with clean rice straw |
| Fermentation time | 3–4 months minimum; up to 1 year |
| Serving method | Grilled over charcoal; no dipping sauce |
| Recognition | Trademark protected 2010 (NOIP); Vietnam Top 100 Specialties 2020–2021 |

## The Flooded Lowlands and the Dish They Produced

Lap Thach sits in the northwest of Vinh Phuc province, in a low-lying agricultural zone criss-crossed by waterways, ponds and seasonal floodplains. Cá thính Lập Thạch có nguồn gốc từ vùng đồng chiêm trũng của Lập Thạch, Vĩnh Phúc – nơi đây, với hệ thống sông ngòi, ao hồ, đầm lầy phong phú, tạo điều kiện thuận lợi cho các loài cá nước ngọt sinh sôi nảy nở. The annual flood season, roughly the 5th through 10th lunar months, drove enormous quantities of freshwater fish into the paddies and ponds. More fish than the village could consume fresh.

Do không ăn hết, phơi khô và bảo quản khó khăn, chợ thì xa và không có thuyền bè nên người dân đã lấy cá tươi cùng với ngô, đậu rang, muối và lá ổi kết hợp thành món cá thính. Sun-drying failed in the wet season. The market was too far. Ca thinh was the solution – salt, roasted grain, guava leaves, a sealed jar, and time.

What began as a preservation necessity became something else over generations. “No one in Lập Thạch district knows exactly when this dish first appeared, but it dates back many generations,” said elderly villager Phạm Thu Hải. “The dish is a source of pride for Lập Thạch people. It has become a traditional favourite not only among locals but also among visitors to the province.”

## Thinh – The Technical Core

### Why corn and soybean, not rice?

Thính được làm từ hỗn hợp ngô với đỗ tương có độ ngon và thơm hơn. Rice thinh is used in other Vietnamese fermented foods, but the Lap Thach tradition favours corn and soybean. Roasted corn contributes a buttery, slightly sweet fragrance; roasted soybean contributes nutty depth and protein. The combination produces a more complex aromatic profile than single-grain thinh.

### Why coarse-pounded, not fine-ground?

This is the single most important technical detail in the entire recipe. “Đặc biệt, hỗn hợp được đem giã nhỏ thành hạt li ti chứ không nghiền mịn như bột. Cách làm này giúp thính không dính bết vào cá. Cá cũng giữ được độ khô, đảm bảo thịt săn hơn, không bị tanh hay chảy nước.” In other words: coarse granules sit loosely against the fish, absorb moisture and maintain a dry microenvironment in the jar. Fine powder turns into a wet paste that traps moisture, interferes with lactic fermentation and degrades the texture. Producers who use electric mills tend to produce inferior ca thinh for this reason.

🌽**Roasted corn and soybean thinh – pounded to coarse granules, the texture that makes this dish work**

## The Role of Guava Leaves

Guava leaves (la oi) layered between the fish in the jar are not decorative. They serve two documented functions:

- **Natural antimicrobial:** Guava leaves contain high concentrations of tannins, quercetin and other polyphenols with demonstrated antimicrobial properties against food-spoilage bacteria. In the jar environment, they help lactic acid bacteria (which produce the desired sourness) outcompete putrefying organisms.
- **Herbal fragrance transfer:** Over three to four months, the leaves slowly release a subtle herbal aroma into the surrounding fish flesh. This creates an additional flavour dimension that distinguishes Lap Thach ca thinh from fish fermented without guava leaves.

The leaves are specified as “medium-aged” – too young and they lack tannin concentration; too old and they become brittle and their fragrance diminishes. Both are washed and fully air-dried before use – any surface moisture on the leaves can disrupt the jar’s dry environment.

## Step by Step – How Ca Thinh Is Made

### Step 1 – Prepare and salt the fish

Scales are left on – they maintain the shape of the fish during fermentation and protect the flesh surface. All entrails and the dark membrane inside the belly are removed. The fish is rinsed, drained and cut into sections approximately 4–5cm long, with light scoring on the flesh to allow salt and thinh to penetrate. Tỷ lệ phổ biến nhất là 10kg cá tươi với 1,5kg muối. In summer heat, producers add a little more salt to prevent early spoilage. After 2–3 days, all the liquid drawn out by the salt is squeezed out and discarded.

### Step 2 – Make the thinh

Dry-roast corn and soybean separately in a clean pan over low heat, stirring constantly until golden and fragrant. Cool completely – pounding warm grain produces something closer to paste than granules. Pound in a mortar to coarse granules; stop well before it becomes powder. The result should look and feel like coarse breadcrumbs, not flour.

### Step 3 – Pack the jar

Cá ướp xong thì vắt hết nước, cho thính ngô và đậu vào bụng cũng như mang cá, bóp kỹ, xếp vào lọ sành phơi khô. Stuff thinh into the belly cavity and rub it over every surface of each piece. In a dry terracotta jar: fish – guava leaves – a scattering of thinh – fish – guava leaves, continuing until the jar is full. Cứ mỗi lớp cá lại cho một lớp lá ổi rồi xếp rơm khô đã vò kỹ, rũ sạch, không còn lá chân lên trên đầu lọ để ủ trong khoảng 3 tháng thì lấy ra nướng than hoa.

### Step 4 – Ferment 3–4 months

Store in a cool, shaded location. Check the rice straw seal regularly: wet straw is the primary risk in long fermentation. Quá trình này được lặp lại khoảng ba lần, sau đó cá được nướng hoặc rán chín. When ready, the flesh inside will have turned a deep pinkish-red – the colour traditionally described as “mận chín” (ripe plum). The thinh granules will still have some residual crunch despite months of contact.

> Ms Hoa, who runs a ca thinh production unit in Lap Thach, told me that the thing she fears most is not losing one jar but losing a batch. A summer when the rice straw seal gets wet undetected means ten jars of three-month fermentation gone. “Unlike pickled vegetables where you can still salvage something – ca thinh that goes bad is gone immediately, there’s no recovery.” Three months of waiting is three months of not being able to check.
> 
> — Kelly Thuy, field notes, Lap Thach, Vinh Phuc

🏺**Terracotta jars of ca thinh – fish layered with guava leaves, sealed with clean rice straw for 3–4 months**

## The Flavour After Fermentation

Món đặc sản này không khô như cá mắm biển cũng không bị nhão như khi ăn cá tươi hoặc cá rán nên rất bắt vị. This middle-ground texture and flavour is what distinguishes ca thinh from every other Vietnamese fish preservation method:

|   | Ca thinh Lap Thach | Dried fish | Fish sauce / fish paste |
| --- | --- | --- | --- |
| Flesh texture | Firm but moist; not desiccated, not soft | Hard and dry, significant moisture loss | Completely liquefied or paste-like |
| Flesh colour | Deep pinkish-red (after fermentation) | Brown, uniform | Brown-black, no recognisable flesh |
| Flavour | Clean mild sourness; moderate saltiness; natural sweetness of fish still present | Concentrated salt; original fish flavour | Very high salt; intense umami; flavour transformed completely |
| Fragrance | Roasted corn + soybean + faint lactic sourness + herbal note from guava leaf | Dried fish characteristic | Fish sauce/paste characteristic |
| How eaten | Grilled over charcoal; no dipping sauce | Fried or braised | Used as condiment or sauce base |

The pieces of fermented fish are coated in a smooth golden layer of rice flour, releasing a rich aroma of roasted corn and beans that instantly makes you crave it. The fish skin is firm and chewy, and the distinctive sour smell blends perfectly with the fragrance of the rice flour, creating a sensory masterpiece.

## Grilling Over Charcoal – The Only Right Way

Producers and families in Lap Thach do not pan-fry ca thinh. Steaming it loses the thinh crust and the fragrance. Pan-frying in oil knocks the thinh off the surface. Only charcoal produces what the dish requires: slow, even radiant heat that warms the thinh coating until it crisps gently while the flesh inside cooks through without drying out.

The moment the thinh hits a medium-hot charcoal grate, the roasted corn and soybean fragrance releases again – the same smell as when they were first roasted, but deeper and more complex from months of contact with the fish. The dish is more enjoyable when grilling over charcoal.

Serve immediately from the grate with plain white rice. No dipping sauce – the salt has permeated through months of fermentation, the lactic sourness is already present, and the roasted grain crust provides its own aromatic texture. Adding fish sauce makes it too salty and masks the clean sourness.

🔥**Ca thinh on the charcoal grate – the thinh crust crisping slowly, roasted-corn fragrance rising**

## Trademark Protection and National Recognition

Năm 2010, Cục Sở hữu Trí tuệ cấp giấy phép đăng ký bảo hộ nhãn hiệu cho đặc sản cá thính Lập Thạch vì quy trình sản xuất đảm bảo vệ sinh an toàn thực phẩm. This was followed by inclusion in the Vietnam Top 100 Specialties 2020–2021.

Today, numerous production units in Lập Thạch cooperate with supermarkets to supply this distinctive delicacy to food lovers nationwide. Cá thính Lập Thạch từng lọt top 100 món ăn đặc sản Việt Nam (2020–2021), hiện được đóng gói, vận chuyển đi khắp nơi. From a village preservation method to a nationally distributed vacuum-packed product – but the three-month fermentation time remains unchanged.

## Where to Buy It

### In Vinh Phuc

- **Lap Thach district directly** – Several production units sell on-site at Van Quan commune and Lap Thach town. The freshest product and best prices.
- **Named producers:** Lan Anh Fermented Fish Facility; Dung Hoa Ca Thinh (Dinh hamlet, Tien Lu commune, Lap Thach); Ba Quy Ca Thinh; Giang Nam Specialties.

### Outside Vinh Phuc

- **Online (Shopee, Lazada, Tiki)** – Vacuum-packed ca thinh from multiple Lap Thach producers. Choose sellers with verifiable addresses in Lap Thach, Vinh Phuc and the registered trademark on the label.
- **Supermarkets in Hanoi** – Some major chains carry ca thinh from partnered Lap Thach producers.
- **When visiting Tam Dao:** Vinh Phuc is approximately 60km from Hanoi; Tam Dao mountain resort is a well-known day-trip destination in the same province. Ca thinh is one of the most common souvenir purchases for visitors.

## Price Reference

| Context | Approximate price (VND) | Notes |
| --- | --- | --- |
| Direct from producer in Lap Thach | ~150,000–250,000 per kg | Varies by fish type; snakehead typically more expensive than carp or tilapia |
| Vacuum-packed (online) | ~180,000–350,000 per kg | Trademark-labelled; 3–6 months refrigerated shelf life |
| Gift packaging (branded box) | ~250,000–400,000 per 500g–1kg box | Suitable as a provincial souvenir gift |

## Nutritional Value

Estimated based on primary ingredients. No independently verified nutritional analysis of ca thinh Lap Thach has been published. Values vary significantly with fish type and amount of thinh adhered.

| Nutrient | Estimated value / 1 grilled piece (~80–100g) |
| --- | --- |
| Energy | ~150–200 kcal |
| Protein | ~18–25g (freshwater fish – high-quality complete protein) |
| Total fat | ~6–10g (varies: snakehead is leaner than silver carp) |
| Carbohydrates | ~5–8g (from adhered thinh crust) |
| Sodium | High (months of salt fermentation) – eat in moderate quantities if monitoring sodium |
| From soybean thinh | Additional plant protein; fibre; B vitamins from roasted corn |

## Frequently Asked Questions

### What is ca thinh Lap Thach?

Freshwater fish salted, coated with coarsely pounded roasted corn-and-soybean thinh, layered with guava leaves in a sealed terracotta jar and fermented for 3–4 months. After fermentation, grilled over charcoal without any dipping sauce. A specialty of Lap Thach district, Vinh Phuc province – trademark protected 2010, Vietnam Top 100 Specialties 2020–2021.

### What is thinh?

Roasted grain or legume pounded to a coarse texture, used in northern Vietnamese fermented food preparation. For ca thinh Lap Thach, it is roasted corn and soybean, pounded to coarse granules – not fine powder. The coarse texture is critical: it keeps the fish surface dry during fermentation and creates the characteristic slight crunch when grilled.

### Why guava leaves?

Two functions: natural antimicrobial (tannins in guava leaves suppress spoilage bacteria, supporting lactic fermentation) and flavour contribution (a subtle herbal note that transfers into the flesh over months of contact).

### How long does it take?

3–4 months minimum, up to 1 year. The time cannot be shortened – under-fermented fish lacks the sourness, colour change and flavour depth that define the finished product.

### Why no dipping sauce?

Salt absorbed during fermentation plus natural lactic sourness creates a complete, self-sufficient flavour. Adding fish sauce would oversalt the dish and mask the clean sourness that is the dish’s defining characteristic.

### What fish works best?

Snakehead (ca qua/ca lo – Channa argus) is considered the best choice: firm flesh, few small bones, natural sweetness that survives fermentation well. Carp, grass carp, roach and tilapia are all widely used alternatives.

## Conclusion

Some foods cannot be rushed. Ca thinh Lap Thach is a clear case: three months is the minimum, the straw seal must be checked regularly, and a wet seal discovered too late means starting over. What results from that patience is a piece of fish that needs nothing added to it – not sauce, not garnish, not accompaniment beyond plain white rice. The salt, the sourness, the roasted corn and soybean fragrance, the faint herbal note from the guava leaves – all of it is already there, built in over three months in a sealed jar in a cool corner of a house in Lap Thach.

If you visit Vinh Phuc, or pass through on the way to Tam Dao, find ca thinh. Take a piece home, grill it over charcoal, and eat it with nothing else. That is the full picture.

Read more on FoodVietnamese:

- [Thit chua – Muong fermented pork, Phu Tho](#) (another thinh-based fermented food from the same northern midlands region)
- [Banh khuc lang Diem – Bac Ninh](#) (next article in the regional specialties series)
- [Cha ruoi – Vietnamese sandworm omelet, Hai Duong](#) (another seasonal, time-dependent northern specialty)
- [Vinh Phuc food guide – beyond Tam Dao](#)