Tuesday, 11 September 2012

Blue soda bread and home science

One of the brilliant things you can do at home, which is also really colourful, is make your own pH indicator from red cabbage water.  Here's a particular use for it which occurred to me the other day:

Making naturally blue soda bread.

The way this works is that so-called "red" cabbage (which i think of as purple) is very high in an anthocyanin.  The word "anthocyanin" is from the Greek words anthos flower, and kyanos - blue.  Anthocyanins are in fact not necessarily blue but all sorts of colours.  They are also useful in herbal medicine.  For instance, the skins of Sambucus nigra (elder) berries are high in anthocyanins which soothe the throat and are useful in coughs and sore throats.  They are almost entirely tasteless and occur in a wide range of flowering plants with the exception of the Caryophyllales, a large order containing such plants as beetroot and cacti, which instead contain betalains.  These two types of compound are never found in the same species.

Anthocyanins are derived from other compounds called anthocyanidins, whose molecular structure can be drawn like this:

The red numbers show where variations occur in the structure.

The substances occur in petals, leaves and some other parts of the plant, in vacuoles, which are "bubbles" of unorganised liquid surrounded by membrane inside the cells.  The acidity or alkalinity of the liquid determines the colour.  They are also responsible for the colour of some fruit, such as the redness of ripe apples.  They may also stop animals which are attracted to green plant parts, which they then eat, from consuming flower petals, and they also attract pollinating insects to flowers.  Their precise shade of purple is complementary to the green of leaves, so they don't block any light which the plant could use for photosynthesis.  This also means that the older photosynthetic organisms with which the plants had to complete billions of years ago would have been exactly that shade of purple too, so if we ever get to another planet where that quirk in the history of life didn't happen, we'd be quite likely to find that the plants were all the colour of anthocyanins, though only if the star the planet orbited was the same colour as the Sun.


Another aspect of anthocyanins is that they form the purple dye colour which is the easiest rich colour to use on cloth in natural dyeing.  Cotton, for example, dyed with elderberries is initially such a strong colour that it looks completely artificial.  Unfortunately, it also fades much faster in sunlight, probably for that reason.  They are sadly quite unstable.

As you can see from the video, anthocyanins are also excellent indicators.  They turn red in acid and blue-green in alkali.  In a strong caustic soda solution, about which i will soon make a video, they become orange.  The reaction between the sodium bicarbonate and lime juice, incidentally, produces a sodium citrate, of which there are three different types, and releases carbon dioxide, which occurs when any alkaline carbonate is combined with an acid.  Disodium citrate can be used to reduce the discomfort of cystitis and urethritis, and is one of the approximately twenty compounds which can easily be made at home from common organic acids and alkali and alkali earth metal compounds.  Compounds which are combinations of acids and bases are known as salts, so the sodium citrates are good examples of organic salts.

The other thing about all this is that the soda bread, which to be honest i perceive as pale turquoise rather than green or blue, is an example of a blue food.  Genuinely strong blue foods have long been an obsession of mine because there are so few of them, and the ones which are claimed to be blue or called blue usually aren't, such as blueberries, pasta coloured with squid ink or "blue corn".  However, there are a few foods which are genuinely blue, and this is one of them, though being soda bread it's probably partly antinutritional.  Another food which would be blue for the same reasons if it existed would be the Finnish salmiakki, which is high in sal ammoniac or ammonium chloride, mixed with liquorice:

  Besides that, there are rather few, but they would include cornflower or borage petals and raw bruised Boletus fungi:


Borage - Borago officinalis - i actually use this quite a lot, partly for its fatty acids.  There are pyrrolizidine alkaloids in it though, so i'm not incredibly keen, and it tends to go off very quickly which is also annoying.

Boletus - don't know which species, but they turn distinctively blue on cutting.  Not all are edible though, either

Anyway, i don't seem to share the general aversion to blue food and was only fearful of the blue soda bread because i was expecting it to taste like a combination of cabbage and bicarbonate of soda, but surprisingly it turned out to taste absolutely fine and was really nice.  I think i just got lucky with the quantity of soda though.

Unfortunately, this is the second time i've made something non-vegan for a YouTube video in a week, so i need to make amends in some way.