Many Stories

Periodically, I would see news articles claiming that coffee sold on the street in Viet Nam was fake. Some did not further clarify, others claimed it was electronic waste, some said 40% of it contained no caffeine at all.

Now, anyone who has actually had street coffee here on a regular basis can attest that last one is an outlandish claim! What you get is pretty unambiguously strong stuff.

Not willing to believe the nice auntie on the street corner was selling me beverages made from e-waste, I decided to investigate. The first thing I needed was a reasonable (or at least, plausible) test for coffee. So I took a trip to the nearest nhà thuốc and supermarket, and took a look at what I could use.

I recalled that Iodine forms a complex with starch that is a very dark blue color. This process is reversible in the presence of reducing agents -- the iodine needs to be in a particular oxidation state for the blue compound to persist. Caffeine, ascorbic acid, and various compounds found in both coffee and tea are quite good reducing agents.

So I designed a test that uses the iodine-starch compound with known iodine concentration as an indicator agent, and I would add diluted coffee at measured volumes until the color disappeared. This is called an iodometric titration, one of the less-popular chemical assays. For starch, I used tapioca -- good value for money.

(You'll have to excuse the photos, I was still saving up for a camera when I did this)

Left: the iodine solution, and Right: the blue starch-iodine complex

The Market... OF DEATH

The chemical market in HCMC (chợ Kim Biên) is nicknamed "The market of death". I go there a few times of year to buy things like chemicals and brass plates. It's not actually horrible. I went searching for materials to make fake coffee. The first thing I found for flavoring coffee was pretty funny, and not at all what I expected:

Is it fish oil or whale oil (of death)? Did whalers ever put whale oil in their coffee? Mysteries abound.

I asked around the market, and eventually someone was kind enough to direct me towards less exotic artificial flavors. Unsurprisingly, it was a dense black liquid that smelled strongly coffee-adjacent. Finally, coffee flavoring! Of death.

Standardization!

Next up, I decided on a standard weight of Trung Nguyên S (the cheapest finest coffee in Viet Nam) to use to make my control samples. Then I mixed up some weaker and stronger coffee, and some fake coffee. I numbered the samples, then randomized them, then titrated them. Only after did I match up the volume required to titrate each with the contents -- I didn't want to accidentally bias myself.

After titration, the sample goes from blue to milky brownish-purple.

Sampling!

The test seemed to work OK at differentiating fake from real coffee. I could also tell the stronger and weaker samples apart.

So, I drove around the city, buying all the street coffee I could find, also recording the exact location of each purchase. I brought them back home, diluted them to the standards I had set earlier, and randomized them. I made two samples from each purchase.

The results were... boring. I found zero cases of fake coffee. In fact, everything tested just fine. So I charted the exact titration amounts against distance from the market (again, of death), in case people nearby the market used weaker coffee and a little flavoring . No relationship! All OK.

So I'll just wrap up with a photo of the lovely death market.

Much nicer than the (unrelated) roundabout of death, which is in fact quite deadly.