DIY Agar

Added on by Justine de Valicourt.

Project: Agar extraction from Gracilariaceae spp.
Start date: Summer 2013
Researcher: Justine de Valicourt
Goal: To extract agar from Gracilariaceae spp. and compare the results of two techniques by clarity, yield, strength and ease of method.

Working with algae was one of the lab’s first projects, and it gave a lot of results: from developing further applications for Nordic species of kelp and dulse to a scientific paper published in Flavour Journal on seaweeds for umami taste. In addition to aroma and umami, some species also exhibit interesting textural properties – indeed many commercially available hydrocolloids are derived from algae species.
In the summer of 2013 I wondered if we could take our seaweed research further and develop our own agar at the lab. Agar is found naturally in species of Gracilariaceae – a family some species of which grow in some of Denmark’s fjords. We obtained some of ours, Gracilaria vermiculosa, from Holckenhavn Fjord on the Danish island of Fyn, and also made trials with dry one from a local hydrocolloid company CP Kelco and a fresh salted one from Roland Rittman, a local forager based in southern Sweden.

Techniques

1. Simple extraction by heat (Neutral Agar/NA)
a) Rinse the algae in clear water a few times until the water stays fresh (clear and unsalty).
b) Cook in a pressure cooker at 15kPa (~120°C) for 2 hours.
c) Pass through a sieve and press so the algae are puréed through it.
d) Let it gel.
e) Freeze.
f) Thaw.
g) Decant and discard the clear water.
h) Dehydrate in fine layers. Conserve in a dry environment.

2. Extraction using heat, NaOH (lye water) and sun bleaching (Lye water Agar/LA).
a) Rinse the algae in clear water a few times until the water stays fresh (clear and unsalty).
b) Cook in a 5% solution of NaOH, with ~500mL of solution per 50g rehydrated or fresh algae, for 2 hours at 85°C.
c) Rinse and put in fresh water under the sun for 5 hours or more.
d) Rinse and conserve in cold water overnight.
e) Cook in a pressure cooker at 15kPa (~120°C) for 2 hours.
f) Pass through a sieve and press so the algae are puréed through it.
g) Let it gel.
h) Freeze.
i) Thaw.
j) Decant and discard the clear water.
k) Dehydrate in fine layers. Conserve in a dry environment.

3. Extraction using heat and sun bleaching (Sun Agar/SA).
a) Rinse the algae in clear water a few times until the water stays fresh (clear and unsalty).
b) Keep in the sun for 5 hours or more.
c) Rinse and conserve in cold water overnight.
d) Cook in a pressure cooker at 15kPa (~120°C) for 2 hours.
e) Pass through a sieve and press so the algae are puréed through it.
f) Let it gel.
g) Freeze.
h) Thaw.
i) Decant and discard the clear water.
j) Dehydrate in fine layers. Conserve in a dry environment.

Fresh Gracilaria soaking to remove salt

Fresh Gracilaria soaking to remove salt

Gracilaria in the process of sun-bleaching

Gracilaria in the process of sun-bleaching

early prototype of dried extracted agar, in sheet form

early prototype of dried extracted agar, in sheet form

Results

Table 1. appearance, smell and yield of six different trials using the three tested techniques

Table 1. appearance, smell and yield of six different trials using the three tested techniques

LA technique vs. NA technique

LA technique vs. NA technique

Observations

The NA technique was mostly done with the salted fresh algae and the dry one, and the SA was tried only with the self-picked Gracilaria from Fyn. The LA technique was used with all the sources of seaweed as a base for comparison and because the LA result from the first experiment was the most prime – it looked and smelled the best. We tried to make a 0.7% gel from the dehydrated LA and the result was slightly less strong than the one from a commercially extracted agar powder. The NA worked too, with a gel almost as strong as the LA one; however, it was greenish with some seaweed taste, and a disturbing wet dog smell.

Next steps will be to try the technique on a bigger scale, and to see if we can improve the clarity and neutrality of the result obtained from the self-harvested algae.

Fresh Gracilaria harvested in Holckenhavn Fjord on Fyn.

Fresh Gracilaria harvested in Holckenhavn Fjord on Fyn.

Conclusion

I recommend the technique using lye water and sun bleach, both for the neutrality of taste and colour. The source of the Gracilaria has a big influence on the final result, and we want to work more on achieving a neutral taste and colour with the self-harvested seaweed. Our techniques for cleaning and bleaching it can be improved. Ultimately I was satisfied to discover that it is possible and quite easy to produce one’s own agar at home with very little equipment.


This technique has been adapted from:

Li, H. and J. Huang, Journal of Applied Phycology, Optimization and Scale-Up of a New Photobleaching Agar Extraction Process from Gracilariacea Lemaneiformis. April 2009, Vol.21 (2) p 247-254.