Pichit Sheet – Explanation and Review

Pichit sheet (pichitto shīto, ピチットシート) is a contact dehydration sheet manufactured by the Japanese company Okamoto Industries, Inc. (オカモト株式会社). Okamoto was founded in Tokyo in 1934 and is a diversified manufacturer of plastic films, rubber products, and consumer goods; the Pichit sheet belongs to the company's food hygiene product line. The sheet removes water and odor-active compounds from food – particularly fish, meat, and seafood – through osmotic pressure. In professional Japanese kitchens and among dedicated home cooks, it serves as a preparation tool for sushi and sashimi.

SUSHIPEDIA. Thawing Tuna with Dehydration Film. All rights reserved ©

Pichit sheet first came to our attention during a stay in Japan. One evening in spring, we sat at the counter of a small sushi restaurant in Shimoda – one of those establishments that are barely recognizable from the outside and where the chef works at arm's length from the guests. Between courses, the sushi shokunin (寿司職人, sushi craftsman) stepped briefly into a back room and returned with a saku (柵, rectangular fillet block) and two fillets, each wrapped in a semi-translucent sheet. The material resembled rice paper but was denser and visibly adhered to the flesh. He unwrapped the pieces with practiced hands and placed them in the refrigerated display case at the counter. When asked, he explained that it was a dehydration sheet he used to prepare his neta (ネタ, toppings) – depending on the fish, for one hour or overnight. He used the sheet predominantly when thawing frozen tuna, as it absorbed the drip loss released during the process and allowed the flesh to thaw without loss of quality. After returning home, we used the sheet regularly over a period of more than one year – the results of this application are documented in the section on individual ingredients.

SUSHIPEDIA. Structure and Functionality of the Pichitto Film. All rights reserved ©

Pichit sheet consists of two semipermeable membrane films based on polyvinyl alcohol, between which a highly osmotic food-grade sugar (glucose syrup) as the dehydration agent and a water-binding algal component (sodium alginate, E401) are enclosed. The seaweed extract increases the viscosity and consistency of the glucose syrup (mizuame, 水飴).

When a food item is wrapped in the sheet, the molecules dissolved in the tissue water create a chemical potential difference between the food and the sheet. This osmotic pressure causes water, odor components, and other low-molecular-weight substances to migrate through the membrane into the sheet.^1, 2

SUSHIPEDIA. Functionality of the Pichit Film. All rights reserved ©

The degree of dehydration depends on the moisture content of the respective ingredient. Effectiveness is higher in lean flesh – such as flatfish – than in fatty flesh. Duration and intensity vary according to species, size, and origin of the fish. In addition to treating raw ingredients, Pichit sheet can also be used for gentler thawing of frozen foods, as the sheet continuously draws moisture from the surface.³ For the production of himono (干物, dried fish), the flesh can be salted before wrapping to enhance absorption. With sufficiently long application times, Pichit sheet is also suitable for producing dried foods.⁴

Although Pichit reduces the water content of food, the sheet does not replace a conventional dry-aging process. In classical aging, enzymatic processes break down the proteins in the flesh, intensifying flavor and altering texture. The flesh also loses moisture and becomes firmer during this process. The moisture loss, however, likely has less influence on flavor than the enzymatic changes themselves.⁵ Water content significantly affects the sensory properties of raw fish. Moisture also constitutes a potential substrate for bacteria that influence both odor and spoilage. A reduced water content further enables flesh to absorb a subsequent marinade more effectively.¹

Drip loss occurs primarily in foods that have been frozen and release a portion of their tissue fluids during thawing. The extent is largely determined by the freezing method and its speed.⁶ High drip loss can impair flavor and texture. When lipid-oxidation-promoting substances are present in the tissue, off-odors and diminished flavor may result. By using a contact dehydration sheet, this liquid is continuously drawn away from the flesh, which can reduce quality loss and extend shelf life.^3, 7

If the Pichit sheet remains on the flesh for too long during thawing, the surface may develop a less appealing texture. Depending on the intended use, it may therefore be advisable to remove the skin before preparing sushi or sashimi. For very large pieces with correspondingly longer thawing times, a sheet with low absorption capacity (product color blue rather than green) is more suitable.

Three variants of Pichit sheet are currently available on the market, differing in their absorption rate.

SUSHIPEDIA. All rights reserved ©

The Pichit sheet with low absorption (マイルド ＜低吸収タイプ＞) has the lowest absorption rate of all three variants. Okamoto markets this variant explicitly for sushi neta and sashimi as well as for cold storage and freshness management of fresh ingredients.

The variant with medium absorption rate (レギュラー ＜高吸収タイプ＞) is, according to the manufacturer, intended for cooking preparations, freezing, thawing, and longer drying processes. Due to its moderate absorption, it is suited – according to Okamoto – for drawing moisture away from food during the thawing process.

Pichit with the highest absorption rate (スーパー ＜超高吸収タイプ＞) is suited, according to Okamoto, for the production of dried fish and dried foods.

SUSHIPEDIA. Usage of Pichitto Film for Sashimi. All rights reserved ©

Pichit can be used for whole fish, though better results are achieved with thin fillets, fillet blocks (saku, 柵), or already sliced flesh – particularly when preparing sushi and sashimi. The flesh should be thoroughly cleaned, blood vessels emptied, and tissue free of hematomas.

The sheet must not be cut, as the contents would leak out. Both sides of the sheet are identical. The flesh is placed on the sheet and fully wrapped, with the sheet pressed as closely as possible against all sides. Excess sheet material can be folded or rolled over itself.

The wrapped flesh is stored under refrigeration. Over time, water accumulates inside the sheet. Storage duration depends on the desired results and the type of flesh. Larger fillets or saku blocks require a longer application time than smaller pieces. When unwrapping, the flesh may adhere slightly to the sheet; careful and slow unwrapping is therefore advisable. Once the desired degree of dryness is reached, the flesh can be prepared directly or flavored with additional ingredients.

In kobujime (昆布締め, kelp curing), fresh ingredients – typically fish or seafood – are placed between layers of kombu (昆布, kelp). The natural umami properties of the kombu intensify the flavor of the ingredients while simultaneously extending their shelf life. The kelp sheets not only transfer their flavor to the food but also absorb moisture, making the fish firmer.

The mechanism of Pichit differs fundamentally from the processes involved in kobujime. At the end of the respective application, however, the treated ingredients are similar in consistency. The flavor of ingredients treated with Pichit sheet remains substantially more neutral, as no flavor transfer from kelp takes place.

In the preparation of sushi and sashimi, it is common to dust ingredients with salt (shiojime, 塩締め, salt curing) or sugar (satōjime, 砂糖締め, sugar curing) before processing. Dusting draws water and other substances from the flesh, which can improve flavor and odor. However, this produces a potentially unwanted salty or sweet aftertaste. To remove it, the flesh is subsequently rinsed with water or sake (酒) brewed from polished rice. This rinsing, however, causes a degree of moisture reabsorption. The use of Pichit sheet offers the possibility of forgoing salt or sugar altogether: the flavor is preserved and odor-active compounds are reduced.

The following section describes our experience with a selection of regularly prepared ingredients. The assessments are subjective and were not produced using scientific methodology. Some individuals preferred the untreated flesh, while others found the drier, firmer texture more appealing. With regard to odor reduction – particularly in fish with a pronounced inherent smell – Pichit proved to be a suitable alternative to salt treatment (shiojime).

Not all ingredients gain in flavor through the use of Pichit sheet. In addition to particularly fatty fish, aquaculture-raised fish can be problematic. Depending on water quality and feed composition, these may exhibit a significant off-flavor. If the flavor is only subtly present in freshly slaughtered specimens, dehydration can intensify it – the water removal concentrates all substances dissolved in the tissue, including undesirable flavor components.

Several applications on Atlantic farmed salmon (sāmon, サーモン) demonstrated that the high fat content prevents adequate water uptake. The flavor differences after five hours (block/fillet) were minimal. Only after an application time of 30 hours did an improvement in flavor become apparent. The application time thus considerably exceeds the general reference values in the table, attributable to the particularly high intramuscular fat content of farmed salmon. Better results were obtained with leaner salmon flesh – pieces from the lean section are therefore preferable.

Lean tuna flesh (akami, 赤身) gains noticeably in flavor when combined with Pichit. After as little as one hour, a perceptible improvement in consistency and flavor intensity is evident. With longer application, the flesh becomes markedly firmer and the color intensifies. The fattier the flesh, the less pronounced the improvement through Pichit.

For the preparation of zuke maguro (漬けマグロ, soy-marinated tuna), thawed saku blocks of yellowfin and bluefin tuna were used. For lean flesh, a dehydration time of two to three hours provides a good base for marinating. Treatment with Pichit sheet allows the marinade to penetrate deeper into the flesh.¹ In our application, the dehydrated tuna flesh was subsequently vacuum-sealed in a bag and marinated in soy sauce (shōyu, 醤油) for 2–3 hours. As a reference value, a soy sauce proportion of approximately one quarter relative to the weight of the flesh proved effective.

The results with flesh from Japanese amberjack (buri, 鰤) vary considerably depending on personal preferences. In young farmed Japanese amberjack – referred to as hamachi (ハマチ) – the consistency became firmer, the odor was reduced, and the flavor intensified, with the umami note becoming more distinct through concentration. In wild-caught fish or larger specimens, the improvement was less pronounced. When thawing frozen farmed hamachi, Pichit sheet proved helpful. Due to the generally higher fat content, significantly longer application times should be expected.

SUSHIPEDIA. Preparation of Madai Sushi with Pichitto Film. All rights reserved ©

The flesh of sea bream (tai, 鯛) has a water content well suited for Pichit. The red sea bream (madai, 真鯛) we used came from Japanese aquaculture operations and was of good quality. The filleted flesh was already free of notable off-odors before application – tender and flavorful. Through Pichit, the flesh lost noticeable amounts of water and became pleasantly firmer. The mildly sweet flavor intensified and the mineral notes gained in presence.

The flesh of most flatfish, such as hirame (鮃), has a relatively high water content, making treatment with Pichit a natural choice. The flesh gains firmness within a short time and the mineral flavor intensifies. The sheet is particularly useful during seasons when the flesh carries a higher fat content, as the "melting sensation" is preserved despite the increased firmness. The thin flesh, however, loses moisture relatively quickly, so the application time should not be excessively long – otherwise too much of the delicate consistency is lost. For larger specimens caught during the cold season, an application time of five to seven hours proved to be a suitable reference value. The resulting consistency is comparable to treatment with kobujime.

In fatty flesh – such as Greenland halibut – the application time is extended. Flatfish caught in winter may also have a higher fat content than those caught in summer.

Japanese sea bass (suzuki, 鱸) is equally well suited for Pichit as for kobujime. The flesh has a high water content, so the application time can be kept short. It is generally somewhat longer than for kobujime. Dehydration renders the mineral flavor slightly more pronounced and the flesh gains firmness. With suzuki, however, texture is a defining quality marker – the flesh depends on its fine, almost delicate structure. The degree of firming through water loss must therefore be carefully weighed, as excessively long application can alter the mouthfeel unfavorably.

Pichit dehydrates through osmotic pressure; the mechanism differs fundamentally from enzymatic aging (dry aging). Effectiveness correlates inversely with fat content: lean flesh responds more strongly, while fatty flesh requires considerably longer application times. White-fleshed fish (shiromi, 白身) – such as flatfish, sea bass, and sea bream – are best suited. Seafood with very high water content – scallops, cuttlefish, squid – lose too much of their characteristic consistency through Pichit. Fish valued for their visual appearance (hikarimono, 光り物) are also less suitable, as the sheet alters the skin surface. In aquaculture-raised fish, Pichit can intensify existing off-flavors rather than diminish them.

Compared to kobujime, Pichit does reduce odor-active compounds but adds no flavor components. The dehydration is flavor-neutral – the aromatization that occurs through kombu does not take place.

For the sake of transparency, the mention of specific products or companies in this article is independent and without promotional intent. No fees were received for the preparation of this text, nor did the author accept free products or services. Furthermore, the author maintains no direct or indirect business relationships with the entities mentioned and holds no equity in them. The information and views shared here serve exclusively the purpose of objective reporting and are based on an impartial assessment.