Vol. XXXIII · Modern Techniques and the Frontier Plate 2 of 11hydrocolloids, xanthan gum, gellan, agar, gelatin, methylcellulose, carrageenan, gels, thickeners, setting temperature, melting temperature, hysteresis, shear thinning, fluid gel, hot gel, vegan gelMT

Hydrocolloids.

A spoon of methylcellulose batter dropped into hot water sets at once; as it cools on the plate, it melts. It is the gel that runs backwards.

Starches and gelatin are hydrocolloids every cook uses (VII.2, X.8). Modern kitchens add others, used by weight at tiny concentrations (a scale reading 0.01 g helps). Xanthan gum, made by bacterial fermentation, thickens at 0.1–0.5 % without heat, is stable to acid, salt and freezing, and is shear-thinning: thick at rest, it flows when stirred, poured or swallowed, so a sauce holds on the plate but does not feel gloopy. Agar, from red seaweed (X.9), sets at about 35–40 °C and does not melt until about 85 °C, so its gels survive warm plates. Gellan, another bacterial gum, makes clear, firm, heat-stable gels and — sheared as it sets — "fluid gels" that pour but hold particles in suspension.

Gelatin, from collagen, sets in the fridge and melts at about body temperature (X.8): that is its charm in the mouth and its weakness on a warm plate. Methylcellulose, made from plant cellulose, is the odd one out: it dissolves in cold water and gels on heating, around 50–60 °C, then melts again on cooling — used to bind plant-based burgers that hold together while they cook (XXXIII.8), and for hot "ice cream" that melts as it cools. The difference between where a gel sets on cooling and where it melts on heating is called hysteresis, and it is large for agar and gellan, small for gelatin. The workshop warms and cools a gel.

Below: the firmness of a gel of the hydrocolloid you choose across temperature, on cooling from hot and on warming from cold (teaching curves around published setting and melting temperatures), with its state at the temperature you choose.

What you will learn

Choose a thickener or gelling agent.
Explain setting, melting and hysteresis.
Use xanthan, agar, gellan and methylcellulose.
Make a hot gel and a fluid gel.

Workshop

Teaching curves (logistic, 2–3 °C wide) around typical published temperatures at common use levels: gelatin (1.5 %) sets ≈ 15 °C, melts ≈ 32 °C; agar (0.8 %) sets ≈ 38 °C, melts ≈ 85 °C; gellan, low acyl (0.5 %) sets ≈ 45 °C, melts above 90 °C; methylcellulose (1.5 %) gels on heating ≈ 55 °C, melts on cooling below ≈ 30 °C; xanthan (0.3 %) thickens without gelling at any temperature.

Pick the gel for the plate

Read the curves at body temperature, 37 °C: gelatin is already melting — it dissolves on the tongue; agar and gellan stay firm far above it, so a warm agar jelly can be served on a hot dish; methylcellulose is liquid at room temperature and sets only when heated. The gap between the blue and red curves is the hysteresis: about 47 °C for agar (it sets at 38 and melts at 85), so an agar gel can be cut, warmed and served without melting.

Using them: weigh to 0.01 g; disperse powders before hydrating (blend xanthan into the liquid with a hand blender, or mix agar and gellan with sugar first) to avoid lumps; agar and gellan must be boiled for a minute or two to dissolve, then set on cooling; gelatin is bloomed in cold water and dissolved below the boil; methylcellulose is dispersed in hot water and then chilled to hydrate before heating to set. Typical amounts: xanthan 0.1–0.3 % to thicken a vinaigrette or sauce; agar 0.5–1 % for a firm jelly; gelatin 1–2 % (or 3–4 leaves per 500 mL) for a soft set.

At the stove

Make two small jellies of the same juice, one with gelatin and one with agar. Put both on a warm plate and watch which melts.

Agar was discovered in Japan in the seventeenth century, when, the story goes, an innkeeper threw out leftover seaweed jelly in winter and found it freeze-dried by morning; as kanten it is still sold in dried bars, and since the 1880s it has been the medium on which bacteriologists grow microbes.

Terms

Xanthan: A shear-thinning bacterial thickener, used cold at 0.1–0.5 %.
Agar / gellan: Firm, heat-stable gels that set on cooling.
Methylcellulose: Gels on heating, melts on cooling.
Hysteresis: The gap between setting and melting temperatures.

Hydrocolloids work at tiny doses: xanthan thickens cold and thins when stirred; agar and gellan set ≈ 40–45 °C and stay set to 85–90 °C; gelatin melts below body temperature; methylcellulose sets when hot. Weigh to 0.01 g and disperse before hydrating.

Sources

H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.
A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.