The companion working paper makes one clean claim: colour is chemistry you can see. Verified A carrot is orange because β-carotene absorbs blue-green light near 450–470 nm; a tomato is red because lycopene absorbs a little further toward 470–505 nm; a blueberry is purple because anthocyanins absorb around 510–540 nm. The pigment is the nutrient, and the wavelength it steals from white light is a direct readout of its electronic structure. When colour tracks a nutrient, your eye is already a crude spectrometer.
But most of what feeds you is colourless. Fat, protein, starch, soluble fibre, vitamin C, the bromelain in a pineapple — none of them absorb visible light, so none of them have a colour to give away. A block of lard and a block of paraffin look alike; egg white and clarified gelatin look alike; the eye cannot tell a healthy oil from a rancid one. The nutritionally decisive middle of a food is exactly the part the eye is blind to.
DRIFTS is Diffuse-Reflectance Infrared Fourier-Transform Spectroscopy. Verified It works in the mid-infrared, roughly 4000 down to 400 cm⁻¹ (wavenumbers). Where visible light moves electrons, infrared light of these frequencies makes chemical bonds stretch and bend. Each functional group — a C–H bond, a carbonyl, an amide, a hydroxyl — vibrates at its own frequency and absorbs there. The result is a fingerprint: not a single colour, but a whole comb of absorption bands that says which chemical groups are present and roughly how much of each.
The "diffuse-reflectance" part is what makes it an industrial instrument rather than a bench curiosity. Ordinary transmission IR needs a thin, clean, transparent sample. DRIFTS instead bounces light off a rough, opaque, granular surface — a powder, a milled grain, a feed pellet, a granola crumb — and collects the light that scatters back out. Little to no sample prep; you can point it at real material. The scattered signal is linearised for concentration through the Kubelka–Munk relation,
where \(R_\infty\) is the measured diffuse reflectance, \(k\) an absorption coefficient (rising with the concentration of the absorbing group) and \(s\) a scattering coefficient. Verified The point is only this: the raw bounce is turned into something that grows roughly in step with how much of a compound is there.
| Band (cm⁻¹) | Vibration | What it reports |
|---|---|---|
| ~3200–3550 | O–H / N–H stretch | water, hydroxyls, amines |
| ~2850–2960 | C–H stretch (aliphatic) | fats & oils, lipid chains |
| ~1745 | C=O ester carbonyl | triglycerides — the fat itself |
| ~1650 / ~1540 | amide I / amide II | protein backbone |
| ~1000–1150 | C–O stretch | sugars & starch |
| <1500 (fingerprint) | coupled modes | molecule-specific ID (e.g. ascorbic acid) |
Book 6 already carries the Parr oxygen-bomb calorimeter. Burn a sample completely inside the bomb, measure the heat, and you get its gross calorific value — how much energy is in it. Verified That is one axis of any feedstock or food. But calorimetry is deliberately blind to structure: it reduces everything to a single number of joules and cannot tell protein from fat from fibre, or a nutritious oil from a spoiled one. It answers "how much energy," never "made of what."
DRIFTS is the other axis. It says nothing about total energy and everything about composition — which functional groups, in what proportion. Put the two together and you have both coordinates of a material:
Energy and composition together are what you actually need to know about anything you intend to burn, ferment, feed, or eat. That is the whole reason both instruments live in the applied line of this book.
The applied thread of Book 6 — Aperiodic Multiplying Media — is about growing nutrition on structured substrates: fermentation and culture media, feed formulation, bioreactor scale-up. Every one of those processes has the same blind spot. You are transforming biomass, and at each step you need to know what the material has become — is the culture accumulating protein or just water, has the substrate been consumed, is the product the fat you wanted or a rancid isomer of it? Colour will not tell you. A calorimeter will not tell you. A composition fingerprint will.
There is a deeper reason a body needs an instrument to read its food, and it is the honest heart of this chapter: we do not make most of our own nutrition. We outsourced it — to plants, to fungi, to bacteria, even to viruses — over tens of millions of years of co-evolution. The colourless middle is colourless partly because it was never meant for our eyes; it was meant to be traded between organisms that grew up entangled.
A plant builds a fleshy, sweet, brightly coloured fruit for one reason: to bribe an animal into eating it and carrying the seeds away. Verified Ripening is literally a colour change — chlorophyll breaks down, carotenoids and anthocyanins show through — advertising "ripe, rewarding" to a disperser. So the working paper's "colour code" has a co-evolutionary floor under its chemical one: plants evolved to broadcast reward, and fruit-eating animals evolved to read the broadcast. (That primate trichromatic colour vision co-evolved specifically to spot ripe fruit against green leaves is a leading hypothesis, not settled fact. Model)
Humans cannot make vitamin C. We carry a broken copy of the GULO gene (L-gulonolactone oxidase); it is a pseudogene, disabled in our primate lineage tens of millions of years ago. Verified The reason it was allowed to break is that fruit reliably supplied the vitamin — so natural selection stopped maintaining the machinery to synthesise it. Our biochemistry assumes a plant will hand vitamin C over. That is interdependence written into the DNA, and it is exactly the kind of colourless nutrient DRIFTS was built to find.
Roughly eighty per cent of land-plant species live in symbiosis with mycorrhizal fungi, trading sugars for the phosphorus and nitrogen the fungi mine from soil. Verified (The popular "wood-wide-web," in which trees consciously share and communicate through the network, overstates it — the nutrient exchange is solid; the altruistic-communication reading is contested. Model) And you finish your own meals the same way: you cannot digest most dietary fibre yourself. Colonic bacteria ferment it into short-chain fatty acids like butyrate, which then feed the cells of your own gut lining; gut microbes also synthesise vitamin K and several B vitamins. Verified Even viruses are in the mix — bacteriophages are the most abundant biological entities in the gut, and by preying on bacteria they tune which microbes dominate, and so, indirectly, what your microbiome makes for you. Model The organism that eats is never eating alone.
Colour is chemistry you can see. Shape is packing you should not over-read. The colourless middle — fats, protein, vitamin C, bromelain — needs the instrument. And the reason it needs the instrument is that this middle was never built for us alone: it is the currency of a trade between plants, fungi, microbes, and animals that co-evolved to feed one another. DRIFTS is how you audit the trade. The Parr calorimeter tells you how much energy changed hands; DRIFTS tells you in what form.