What's the first thing that comes to mind when you think of algae? Is it stagnant water by a busy road, or a long-abandoned swimming pool, with a rather macabre green film floating on top?
If you're a keen follower of the food scene, you'll have instead noticed it popping up more and more in restaurants over the past few years. It is lauded by chefs for its intense flavour – a strong umami kick – and its healthy properties.
And it may have further benefits. According to a Cambridge University professor, spirulina and chlorella, two micro-algaes that form on top of water, could provide a sustainable form of nutrition in the future. Crucially, they can be grown in urban environments and don't need plenty of agricultural land. With the challenge of a changing climate, this could form a vital source of food.
The algae have already infiltrated our supermarkets. Spirulina is increasingly used as a food additive for its nutritional advantages. Full of protein, B vitamins, and minerals such as iron, it can now be found in ice cream, vegan egg substitutes, and protein powders. Some experts, however, warn that some of its nutrients are not bio-available, making it harder for our bodies to absorb them.
The term is a rather broad church. From microscopic algae like spirulina and chlorella, to giant kelp, which can grow up to 50 metres in length, a whole world of photosynthetic organisms are classed as algae.
"Algae and seaweeds are true superfoods", says nutritionist Cassandra Barns. "They're rich in essential minerals which, depending on the type of algae, can include iodine, calcium, magnesium, iron and antioxidant manganese."
To Barns, spirulina is the "rock star" of the algae world. "In its dried form, it's almost two-thirds protein, making it a fantastic protein source for vegans in particular." Spirulina powder can be easily added to smoothies, or it can be taken in tablet form.
Nutritionist and co-founder of Huel (a meal replacement powder made from oats, pea protein, ground flaxseed, brown rice protein, vitamins and minerals) James Collier agrees. "Marine algae has a number of health benefits, most notably it's a rich source of the semi-essential fatty acids EPA and DHA. These omega-3 fatty acids are more commonly consumed in the form of oily fish, and are involved in reducing the risk of heart disease and stroke."
For all the talk of fatty acids and iodine, there's an important factor behind the meteoric rise of algae. "The brilliance behind it is the flavour profiles", says chef Rob Howell, of Root in Bristol. "Because we're a vegetable-based restaurant, we have to think differently. Using seaweed and algae allows us to get more obscure, intense, flavour profiles. That hit of umami."
One favourite at Howell's restaurant was charred hispi cabbage with seaweed butter sauce. "Everyone's obsessed with it," says the chef. "We dry the seaweed out and then blitz it into a powder.
"We make a seaweed vinegar and an oil to go with beetroot. We make a really nice vegetable demi-glace. Instead of gravy or a meat jus, we roast off loads of vegetables with nori and kelp, and reduce it. It's almost a better product than a beef gravy, which is crazy."
The reference to nori highlights another aspect of the algae trend: it's not a modern discovery; people have eaten it for centuries. "There's nothing new about it", says Howell, who often forages for seaweed in Dorset, "it's just a regeneration."
Chef Ryosuke Kishi, of Ginza Onodera in London, explains: "In Japan, we eat over 50 types of algae, and the benefits are well-known, which is part of the reason we have been cooking with algae for thousands of years.
"Algae's popularity also stems from its flexibility. It can be used in stocks, salads, main courses and even in desserts. We use it for soups and hot pots; it has a clean and elegant flavour which is less powerful than a traditional meat or fish stock."
But to Kishi, there's a similarity between Japan and Britain. "As an island nation like Japan, Britain has a lot of similarities in terms of produce. Welsh cuisine for example traditionally uses algae, so I think it's a natural progression." Today, seaweed can be found in a Welsh gin and cheese.
The British may well have a longer history with algae than we think, and Kishi says we're growing more experimental and rediscovering our love affair with sea plants. "We have a soup called 'dobin mushi' that uses kelp stock, which is incredibly popular."
Howell has experienced a similar response at Root. "It's really nice to hear people say, 'I'd never have picked that, but it's absolutely outstanding'."
Apart from certain algae like spirulina, seaweed can be easily found across British shores. Most of Howell's produce is foraged in Cornwall, and he encourages everyone to get involved. While only around 20 of 700 varieties found in Britain are good to eat, they're easy to distinguish, and, unlike with mushrooms, mis-identification isn't a huge problem. But, of course, it's worth checking with an expert before trying for yourself.
Paul O'Connor's Carrot salad with sea spaghetti recipe
15g sea spaghetti
2 tablespoons lemon juice
1 tablespoon rice vinegar
5 carrots, sliced with a potato peeler
For the dressing:
3 tablespoons good-quality olive oil
1 tablespoon lemon juice
1 tablespoon honey
1 teaspoon coarse wholegrain mustard
2 cloves garlic, crushed
A pinch of cayenne pepper
Salt and pepper to taste
Rinse the dried sea spaghetti and soak in warm water for 1 hour or briefly steam until al dente
Rinse the seaweed again and then marinate in lemon juice and wine vinegar for a few hours or overnight
Some can be left full length to decorate - chop the remainder into 5cm pieces
To prepare the salad:
Combine the dressing ingredients in a small jug
Pour the dressing over the carrots and sea spaghetti and allow to marinate for at least an hour