accidental discovery: walnuts can make things purple?

So I’ve made this recipe belonging to a buddy of mine about five times without any anomalies and consistent flavour. It’s a simple method using an immersion blender, comes up a creamy golden brown, with a little separation continuing after a cloth-straining (no big deal as it’s blitzed into a creamy drink). It’s walnuts, honey, vanilla, water.

Out of nowhere this week, and originally to my absolute horror, as I began blending the walnuts into the honey it began to turn purple… and then black. What the hell had I done? What new element had I introduced? It was practically inky and the foam on top was cement grey-purple.

Turns out this is one the coolest accidents to come my way. It was an acid that is commonly found in the skins of walnuts, called gallic acid. After a bit of google searching I ended up on baking and beekeeping forums, and the wikipedia page of an ink used between the 15th-19th centuries, and this is what I’ve got:

  • A problem for bakers is having their walnut breads turn purple because of gallic acids found in the skin.
  • A highly sought after and quite rare type of honey that occurs naturally is dark purple. Many apiarists believe this is because of high acidity in the soil in the vicinity of hives.
  • Iron gall ink was prepared using iron salts and tannic acids from oak gall nuts (where the name for gallic acid is derived.) A well prepared iron gall ink would gradually darken on the paper to a dark purple colour.

I totally triggered a chemical reaction accidentally. Perhaps the honey contained something that interacted with the walnuts? Maybe I didn’t bring the water entirely to the boil?

Now where do I find this actually purple honey, though?

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using acid to clarify homemade orgeats

For a while I was looking for a method to get my pistachio syrup stable, be it cloudy or clear, without using metres of muslin cloth. (pistachio syrup with xanthan). I actually solved this a little while back and after making it a few times have pretty much nailed down an easy method.

The recipe I was using had a splash of unexplained vinegar in it. For most of the time I have been making it I assumed it must have been included as a preservative measure, as with shrubs, as there was no mention of it in the recipes method. One day however, as I was melting sugar into my pistachio milk on the stove, I noticed a thick skin forming on the top of the liquid, and I began to skim it off, as you might while clarifying butter. So many things clicked in my brain at the same time (citric acid in cheesemaking, alternative milks like soy and almond curdling in hot coffee) and that unexplained splash of vinegar suddenly made sense.

Now I bring that stuff to the boil, stand over it at a simmer with a large flat spoon, and skim as much of that gunk from the surface as I can, and then it’s just one pass through few layers of muslin for a perfectly clear syrup. I wouldn’t necessarily use vinegar in every orgeat recipe I made. In this recipe it works because the pistachio syrup is used in combination with a shrub that also contains the same type of vinegar, so the distinctive flavour is balanced in the final drink. It’s definitely worth looking into how small an amount of acid you can add to encourage it to curdle, to reduce the chances of altering the flavour.