Red algae, raw (seaweed, organic?)

Red algae (Rhodophyta) are a phylum of algae that includes a variety of mostly red genera and species. Red algae also include seaweed (marine macroalgae), some of which are edible, even raw . Organic?

Use in the kitchen

What is seaweed? Seaweed refers to the macroalgae in the sea that are visible to the naked eye and that mostly grow on the bottom. This distinguishes them from single-celled or microscopically small microalgae. In the phyla of red algae (Rhodophyta; approx. 6000 species), green algae (Chlorophyta; approx. 1500 species) and brown algae (Phaeophyceae; approx. 1755 species), both microalgae species and macroalgae species (seaweed) are represented. ^1,2

Most seaweed species are red algae. ³ The phylum of red algae (Rhodophyta) includes many algae that are colored red by certain pigments from photosynthesis. However, algae with other colors can also be found in it.

The focus of this article is on multicellular red algae species, i.e. red algae seaweed. Can you eat red algae and is seaweed edible? We also focus primarily on edible seaweed from the red algae, including purple kelp ( Nori ; genus Porphyra ), cartilaginous kelp ( Chondrus crispus ) or dulse ( Palmaria palmata ). What does seaweed taste like? The taste of seaweed ranges from mild and sweet to spicy and salty and can taste slightly fishy depending on the type.

In Europe, you can usually only get dry red algae seaweed. How can you prepare seaweed? You can either use it as it is, or soak it briefly in water so that you can prepare it like fresh seaweed. Red algae flakes are ideal for seasoning all kinds of vegetarian and vegan dishes. They give dishes and broths a welcome umami note.

While the use of seaweed in cooking is not yet widespread in Europe, it is a regular feature on the table in many Asian countries. The best-known form of red seaweed is red seaweed leaves (nori), usually made from purple kelp species. The thin, dry leaves are mainly used to make sushi and gimbap (Korean). In Asia, they are also cooked in soups or used in spice mixtures for ramen, for example. Can nori leaves be eaten raw? Is seaweed vegan? The leaves are usually roasted and therefore not considered raw food. Raw nori leaves do exist, but they are difficult to find and often more expensive. Whether raw or roasted, the leaves are vegan and suitable for raw consumption.

Other commonly used red algae species are the slightly nutty-tasting dulse ( dried dulse ) and the kelp (also called Irish moss), from which the polysaccharide agar is obtained, which is used as a vegan gelatin substitute.

Seaweed is generally suitable for refining salads and soups. For example, you can prepare a classic miso soup, but you can also spice up a creamy soup with cauliflower . A seaweed salad with wild rice, tofu, sesame and spring onions is highly recommended. Stews, risotto, omelettes or even mashed potatoes can also be enhanced with seaweed. Red seaweed also tastes delicious in a vegetable pan with spinach, leek and chili with rice noodles. Dried seaweed also makes a good snack together with dried fruit and nuts.

Vegan recipe for a beetroot and quinoa salad with red algae

Ingredients (for 4 people): 10 g dried red algae (preferably organic), 2 raw beetroots, 1 bunch of radishes, ½-1 chili pepper, 10 g fresh ginger, 1 lime, 2 tbsp soy sauce, 2 tbsp rapeseed oil, 1 dash of agave syrup, 100 g quinoa .

Preparation: Soak the dried red algae in water for about 5 minutes. Meanwhile, peel the beetroot, rinse the radishes and slice both into thin slices. Finely chop the deseeded chili pepper. Peel the ginger and grate finely. Squeeze the lime juice into a bowl. Add the soy sauce, oil, chili, ginger and agave syrup and mix well. Pour half of the dressing over the beetroot and mix. Set the rest aside. Cook the quinoa according to the instructions on the packet. Drain the water from the soaked algae, let it drain and then tear it into pieces. Mix the algae, radishes and quinoa with the remaining dressing. Distribute the beetroot slices decoratively on four plates and arrange the vegan algae and quinoa salad on top.

Vegan recipes with seaweed (red algae) can be found under the note: " Recipes that have the most of this ingredient ".

Purchasing - Storage

Where can you buy seaweed? Red algae as seaweed is mostly found in Europe in dried form and rarely fresh. In large retailers such as Coop, Migros, Spar, Aldi, Lidl, Rewe, Edeka, Hofer, Billa etc. and organic supermarkets such as Denn's Biomarkt and Alnatura you usually only find nori leaves or nori flakes. Smaller supermarkets such as Denner and Volg do not offer the seaweed leaves or only offer them during special promotions. Processed red algae can be found in numerous products, such as ready meals, snacks, noodles (pasta), soup powder or seasoning pastes.

In Asian shops and online stores, you have the chance to find a more diverse selection of red algae. Organic quality is well represented in the online range. You can also buy raw, gently dried red algae leaves online. Raw seaweed leaves can usually be recognized by their dark brown color, while roasted leaves are more greenish.

The availability of seaweed (red algae) varies depending on the size of the store, catchment area, etc. Our recorded food prices for the DA-CH countries can be found above under the ingredient image - and by clicking on them you can see their development at different suppliers.

Storage tips

Dried red algae seaweed will last for years if kept dry, protected from light and in an airtight container. Fresh red algae should be stored in the refrigerator and used within two to three days.

Ingredients - Nutritional values - Calories

The energy content of red algae seaweed (raw) is 35 kcal and is therefore very low. Carbohydrates (5.1 g/100g), fiber (0.3 g/100g) and fats (0.28 g/100g) are also only present in small amounts. Proteins (5.8 g/100g) are not a small amount. The salt content of 122 mg/100g covers 5.1% of the daily requirement. In dried algae, this content is usually somewhat higher, e.g. in dried dulse (366 mg/100g). Dried kombu algae contain unhealthy amounts of salt at 7,112 mg of table salt per 100 g. ⁴

Raw red algae are particularly rich in folate . The content of 146 µg/100g (73% of the daily requirement) is similar to that of frozen spinach (145 µg/100g) and raw kale (141 µg/100g). Raw wakame has slightly more at 196 µg/100g and dried dulse (kelp) has more than eight times the vitamin at 1269 µg/100g. ⁴

The trace element manganese is also present in considerable quantities at around 1 mg/100g (49% of the daily requirement). Raw spinach (0.9 mg/100g) andfrozen, blanched edamame (1 mg/100g) contain a similar amount. Pine nuts contain even more manganese (8.8 mg/100g). ⁴

39 mg of vitamin C are found in 100 g of raw red algae seaweed (49% of the daily requirement). A similar amount is found in lamb's lettuce (38 mg/100g) and white cabbage (37 mg/100g). At 184 mg/100g , yellow bell peppers contain a particularly high amount of vitamin C. ⁴

Many studies indicate that vitamin B₁₂ (cobalamin) is only found in significant amounts in animal foods, meaning that no plant-based food naturally contains sufficient amounts (of the usable form) of vitamin B _12. ^21,22 However, a 2014 study reported the occurrence of the vitamin in dried purple kelp ( Porphyra spp.) and green algae of the genus Enteromorpha . ⁷ We doubt that the amounts contained can cover the daily requirement. A 2017 study also indicates that although many analytical studies attribute significant amounts of vitamin B₁₂ to dried and roasted nori products, it is possible that the drying process and storage destroys the vitamin and/or converts it into inactive B₁₂ analogues. ²³ You can find out more about vitamin B₁₂ in the related article and in the article Vegans often eat unhealthily. Avoidable nutritional errors.

In addition to vitamins and trace elements, seaweed (red algae) also contains significant amounts of essential amino acids such as valine, threonine, isoleucine and leucine .

The complete ingredients of seaweed (red algae), the coverage of the daily requirement and comparison values with other ingredients can be found in our nutrient tables. In the article Nutrients explained you will get a detailed insight into the topic.

Health Effects

Is seaweed healthy? Red algae (seaweed) are rich in bioactive substances and compounds such as proteins, sulfated polysaccharides, pigments, polyunsaturated fatty acids, vitamins, minerals, and phenolic compounds with nutritional and medicinal significance. These exhibit health-promoting properties, including antimicrobial, antiviral, antioxidant, anti-coagulant, anti-inflammatory, antidiabetic, anti-allergic, and analgesic effects. ⁷

The sulfated polysaccharides such as carrageenan, fucoidan, laminarin are particularly worth mentioning. A growing body of research indicates their anti-cancer and antimetastatic properties. Promising areas in the study of the biological activity of carrageenan include its potential use as an agent for activating antitumor immunity, as an adjuvant for therapeutic vaccines and as an antimutagenic agent. ²³

Red algae contain phycobiliprotein, a group of membrane-associated photosynthetic pigments that are unique to red algae, cyanobacteria and cryptophyceae . These are used commercially as anti-inflammatory agents. They also have antidiabetic and antioxidant effects. ²⁷

Secondary plant substances

Many of the health effects of red algae can be attributed to the secondary plant substances they contain. Our article on secondary plant substances provides an overview of the classification of substance groups, their occurrence in food and possible effects on humans. Red algae contain the following secondary plant substances, among others: ^27,28

• Isoprenoids: Diterpenes; Sesquiterpenes; Triterpenes: Steroids (cholesterol, desmosterol, cholesta-4,6-dien-3-ol, cholest-5-ene-3,7-diol); Tetraterpenes: carotenoids (carotenes: alpha-carotene, beta-carotene; xanthophylls: antheraxanthin, cryptoxanthin, lutein, violaxanthin, zeaxanthin)
• Polyphenols: Phenolic acids: hydroxybenzoic acids (gallic acid, protocatechuic acid, genistic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid); flavonoids: flavanols (catechin), flavonols (quercetin, rutin), flavanones (hesperidin), isoflavones (daidzein, genistein)
• Other nitrogen-containing compounds: Mycosporin-like amino acids
• Protease inhibitors: Chlorophyll A, Chlorophyll B

However, it should be noted that the composition of secondary plant substances in red algae can vary depending on the variety, time of harvest and growing conditions. Therefore, quantities are only of limited use and can only be understood roughly. Note: The chemical contents of algae differ depending on the type of algae, growth stage, environment and external conditions such as water temperature, light intensity and nutrient concentration in the ecosystem. In addition, there are some Rhodophyta species whose medicinal potential is higher, such as Gracilaria spp., Pterocladia spp., Jania spp. and Corallina spp. ⁷

Phytosteroids extracted from algae are used in pharmaceutical production and food supplements. Cholesterol is present in very small quantities in red algae, except in purple kelp ( Porphyra sp.), where it accounts for 8.6% of the total steroids. The steroids present have antioxidant, antiviral, antifungal and antibacterial effects. ²⁷

Carotenoids have antioxidant, anti-inflammatory, anti-tumor properties and reduce the risk of eye diseases in humans. Carotenoids from algae are found in everyday products as food coloring and as a component of cosmetics and medicines. Polyphenols have a variety of bioactive properties such as antidiabetic, antioxidant and anticarcinogenic effects. ²⁷

The metabolites of the macroalgae also have a positive effect on the skin. They reduce the appearance of redness and blemishes, remineralise, hydrate and firm the skin. The mycosporin-like amino acids formed by Rhodophyta algae also have a photoprotective effect and help protect against UV rays. The water-soluble, nitrogen-containing mycosporin-like amino acids absorb UV light particularly well and also have an antioxidant, immunomodulatory and anti-inflammatory effect. ²⁷

Read more about the health effects of the secondary plant substances in red algae: purple kelp ( Nori ; genus Porphyra ), kelp ( Chondrus crispus ) or dulse ( Palmaria palmata ).

Dangers - Intolerances - Side effects

Seaweed is a source of the essential trace element iodine . This plays an important role in thyroid function because it is required for the synthesis of thyroid hormones. However, long-term, high intake of iodine can lead to thyroid dysfunction, such as hyperthyroidism or hypothyroidism. A 2020 study determined the iodine content of 30 red algae seaweed samples (dulse and kelp) to assess the iodine burden from consuming dulse and kelp. The results showed that dulse seaweed has a higher iodine content than kelp seaweed, but neither poses a health risk if the recommended daily consumption of seaweed (4 g/day) is observed. Nevertheless, it is necessary for seaweed consumers to follow the manufacturers' recommendations. In addition, the origin of the seaweed plays a role in the iodine content. ⁸

An important component of sushi, which is now eaten almost worldwide, is red algae leaves (nori) . Seaweed salad is often served with it. Therefore, a 2019 study from Greenland investigated the possible acute negative effects of iodine exposure from a single meal of sushi and seaweed salad. Eating a sushi meal, even with Japanese seaweed salad as a side dish, did not lead to excessive iodine intake. Participants who had a Greenland seaweed salad as a side dish exceeded the recommended daily iodine intake. However, this had no negative effects on thyroid hormone secretion, as a short-term increase in TSH completely compensated for the iodine-induced inhibition of the thyroid. The study concluded that the influence of a single iodine intake of this magnitude does not cause any undesirable effects or permanent changes in thyroid function, so a sushi meal is not recommended. ⁹

When buying seaweed products, make sure that the iodine content and a maximum recommended daily intake are indicated. This will help you estimate your iodine intake and avoid over-consumption.

A 2015 study determined the levels of toxic elements (such as aluminum, silicon, arsenic, cadmium and lead) in 14 edible seaweed species (including red algae species). The results showed that although the samples were not free of contaminants, the concentrations were below levels that are hazardous to health. Nevertheless, continuous monitoring of contaminants in edible and marketed seaweed is important. ¹⁰

Folk medicine - natural medicine

The use of red algae is widespread in traditional Chinese medicine . Commonly used genera are Chondrus, Gracilaria, Gelidium, Gloiopeltis and Porphyra . Chondrus is used for bronchitis, tonsillitis, asthma, stomach problems and constipation; Gracilaria for the treatment of goiter, edema, urinary tract infections, chronic constipation, tuberculosis, testicular swelling and for the prevention of ulcers; Gelidium for lung diseases, scrofula, constipation, stomach pain and ulcers; Gloiopeltis for diarrhea, goiter and scrofula; Porphyra for goiter, bronchitis, tonsillitis, sore throat and cough. A solution of the alga Gigartina bracteata was used for menstrual problems. ¹¹

Ecological footprint - animal welfare

Seaweed farming can produce large quantities of nutrient-rich food for human consumption. In addition, marine farming appears to be more sustainable than land-based farming, as seaweed farming does not require fresh water ( water footprint ), chemical fertilizers, or land, which are major negative factors of farming. ¹²

In addition, algae production could absorb many of the excess nutrients that have entered the sea through fertilization and thus purify the water. Algae production could also help combat ocean acidification caused by increasing CO ₂ concentrations in the atmosphere. The production of 500 million tons of algae could absorb 135 million tons of carbon, which corresponds to around 3.2% of the carbon that is added to seawater each year through greenhouse gas emissions. ¹³ Further studies and experiments are needed to determine the effect. In particular, in what form the CO ₂ can be stored in the algae in the long term.

An LCA calculation of agar (vegan gelling agent made from red algae) resulted in a CO ₂ footprint of -1.11 kg CO ₂ eq/kg from raw material extraction to leaving the factory gate ('cradle to gate'). The cultivation of seaweed had a negative CO ₂ life cycle assessment of -7.21 kg CO ₂ eq/kg. This result shows that the carbon uptake by macroalgae can offset the carbon emissions from agar production. ²⁴ This makes red algae an excellent starting product. However, it should be noted that seaweed as a food can only store CO ₂ for a short period of time. ²⁶

Apart from the excellent _carbon footprint, the cultivation of macroalgae provides many so-called ecosystem services: it is good for marine life, reduces eutrophication (too many nutrients in the sea) and reduces ocean acidification. ²⁵ But of course it all depends on the implementation and we must be careful not to make the same mistakes in farming at sea as we do on land. Organic marine products are to be preferred, as is the case with land-based products.

For detailed explanations of various sustainability indicators (such as ecological footprint, _CO2 footprint, water footprint), see our article: What does the ecological footprint mean?

Worldwide occurrence - cultivation

Seaweed has been used as a staple food in China, Japan and Korea since prehistoric times. But people in Europe also used some red algae species early on. A 10th-century Icelandic law book mentions regulations for collecting dulse ( Palmaria palmata ). Dulse has also been used for a long time in Ireland and Scotland. Purple kelp ( Porphyra spp.) has been eaten in Wales since 1600 AD. Irish moss ( Chondrus crispus ) has been considered a medicinal product in Ireland since the beginning of the 19th century. Other red algae have been used in the Mediterranean region since pre-Christian times as a dye and anthelmintic. ¹⁴

The consumption of seaweed in Western countries has increased in recent years. This is primarily due to its beneficial nutrients and the growing number of vegetarian and vegan people who want to eat healthier. ^{8, 10}

Important areas for growing seaweed in Asia are China, Japan, Korea and the Philippines, in North America in California and in Europe in Brittany. Over nine million tons of seaweed are harvested worldwide every year. Of this, 400,000 tons are nori, which is used to make red seaweed sheets for sushi . ¹⁵

Found in the wild

Marine red algae are found at all latitudes. They are more common in temperate to tropical areas than in polar and subpolar regions, where brown and green algae predominate. They can live at depths of up to 200 m. There are also some freshwater red algae species. ³

Cultivation - Harvest

Seaweed can either be collected wild on rocky coasts or artificially cultivated. Both processes can be carried out in accordance with organic standards. When collecting in the wild, it is important to ensure that the collection waters are clean. Collected organic algae therefore come from waters far from busy ports, sewage discharges, nuclear power plants, conventional aqua farms or other sources of pollution. It is also important to harvest sustainably, i.e. only take as much as can grow back. Stocks must be maintained so that other marine life is not harmed by the harvest. ¹⁶

The methods of macroalgae cultivation are varied. The choice of a seaweed species for cultivation is based on the location of the seaweed farm and the cultivation possibilities (in the open sea, on land, in the cold waters of the temperate zone or in the warm waters of the tropics), on the productivity and adaptability of a species, on the dimensional characteristics of an aquatic ecosystem (size and depth) and also on factors such as irradiance, temperatures, nutrients, pollution, water movement and degree of wave action. The choice of cultivation method is based on cost-effectiveness and the intended use of the seaweed (for human consumption or as animal feed, as a source of substances for the production of polysaccharides or medicines). The cultivation methods can be roughly divided into two main groups: extensive and intensive cultivation. ¹⁷

Extensively cultivated algae are grown in natural waters, using only naturally available light, heat, water, kinetic energy and nutrients. Either the naturally occurring algal communities are used or cultures of native or non-native species are introduced. This usually leads to the alteration or even destruction of the naturally occurring biocenoses there. ¹⁷

There are several methods of intensive culture. One method is to cultivate one or more species of algae in tanks using natural or artificial light, nutrients and phytohormones. The other method is to cultivate algae in small natural water bodies (ponds, lakes and lagoons), using organic and inorganic fertilizers and applying agronomic techniques such as weeding, reducing epiphyte growth, regulating light and water movement. ¹⁷

An extensive cultivation method with naturally occurring algae species is desirable in the interests of environmental protection and sustainability. As on land, only organic fertilizers may be used in organic farming. Organic farms must ensure that as few nutrients as possible from the algae farm enter the environment. ¹⁶

Further information

The phylum of red algae (Rhodophyta) comprises two subclasses (Bangiophycidae and Florideophycidae) with a total of seven orders. These in turn comprise several families that produce around 500 genera and ultimately 4000 to ⁶⁰⁰⁰ species. The majority of the species are marine algae - only around 50 species from 12 genera are freshwater algae. In addition, the majority of red algae are multicellular with a visible thallus (vegetative body of the algae) - only a few species are unicellular. ¹⁸

Red algae have evolved in parallel to the other algae strains (green algae and brown algae). The most obvious difference between the strains is their pigmentation. In addition, red algae lack flagellated reproductive bodies. ¹⁸

Bangiomorpha pubescens, a red alga, marks the earliest known expression of multicellularity and eukaryotic photosynthesis in fossil history. The alga is older than 800 million years. ¹⁹

We describe some types of red algae in individual articles: Limu Kohu (red Hawaiian algae), Irish Moss, Dulse (dried kelp), Nori . You will also find articles on the following brown algae: Laminaria (kelp), Arame algae, Bladderwrack, Kombu algae (dried), Wakame . We also write about the blue-green algae (also called cyanobacteria) Spirulina .

Alternative names

Colloquially, seaweed is just called kelp. Red algae seaweed can also be called red seaweed.

The English name for red algae is red algae, and for red seaweed it is red seaweed.

Other uses

The two most important polysaccharides obtained from red algae are agar and carrageenan. They are used commercially as thickeners, stabilizers, emulsifiers and dietary fibers in the food and pharmaceutical industries. ^3,7 Agar is used for gelling and thickening, especially in the preservation of fish and meat. The polysaccharide is also used in the production of processed cheese, mayonnaise, pudding, creams and jellies. In pharmacy, agar is used as an inert carrier for drugs that require a slow release of the active ingredient, as a stabilizer for emulsions and as an ingredient in cosmetic skin preparations, ointments and lotions. Carrageenan is usually obtained from wild populations of carrageenan . Carrageenan is used in a similar way to agar. Carrageenan is more suitable for stabilizing emulsions in paints, cosmetics and other pharmaceutical preparations. ³

Due to the relatively high calcium content of red algae, they are often added to plant-based milk alternatives to increase their calcium content. In addition, algae lime, the mineralized coral deposits of red algae, are used as fertilizer in agriculture and in gardens. ²⁰