Gelling calculator
Gelatin, agar and xanthan by the weight of your liquid
Say how much liquid you have and what texture you want: the dose comes out in grams, with the page it came from. The sheet-to-powder conversion, which is where nearly every recipe goes wrong, comes with it.
It sets in the mould and comes out whole: panna cotta, aspic, fruit jelly.
How much to use
| Agent | Amount | % of liquid |
|---|---|---|
| GelatinGels · No boiling needed · Holds to 37 °C | 4.00 g | 0.8%Myhrvold & Bilet, cap. "Custards and Pies" — "Raspberry Panna Cotta" |
| Iota carrageenanGels · No boiling needed | 0.61 g | 0.12%Myhrvold & Bilet, cap. "Custards and Pies" — "Raspberry Panna Cotta" |
| Kappa carrageenanGels · No boiling needed | 0.47 g | 0.09%Myhrvold & Bilet, cap. "Custards and Pies" — "Raspberry Panna Cotta" |
Iota and kappa go together in this recipe: the mixture lands between the soft gel of one and the firm gel of the other.
- Gelatin — Melts at 37 °C — body temperature, which is exactly why it dissolves in your mouth. No use for anything that will be served hot.
- Iota carrageenan — Makes soft, elastic gels. The source always uses it together with kappa.
- Kappa carrageenan — Makes firm, brittle gels. The source always uses it together with iota.
Sheet or powder: converting by Bloom
The recipe calls for powder and you have sheets — or the other way round. The grade changes the weight, and the source publishes the exact formula instead of the “one sheet per spoonful” guess.
- Use
- 4.00 g
- The published dose is in Knox powder, 225 Bloom
- 4.00 g
new weight = original weight × original Bloom ÷ new Bloom · Bloom 225 → 225
| The gelatin you have | Bloom | g per sheet |
|---|---|---|
| Bronze | 125–155 | 3.3 |
| Silver | 160 | 2.5 |
| Gold | 190–220 | 2 |
| Knox (powder) | 225 | powder |
| Platinum | 235–265 | 1.7 |
Look at the table: the weaker the sheet, the heavier it is. Bloom times grams per sheet lands between 400 and 460 across all four grades — sheets are made to carry roughly the same gelling power, which is why recipes written in “number of sheets” work at all. That reading is ours, not a claim the book makes.
The book also says gold and platinum can replace Knox powder directly. By its own formula that is off by about 10% each way. It is a kitchen shortcut; here we use the formula.
What changes the firmness
The dose is the start. Whatever else is in the liquid changes the gel, and McGee gives the direction of each — direction, not a number: anyone publishing “add 20%” would be inventing it.
- Sets softer
- Salt — it interferes with the bonds between gelatin molecules.
- Sets firmer
- Sugar — it pulls water away from the gelatin. Fructose is the exception.
- Sets firmer
- Milk.
- Sets firmer
- Alcohol — until it reaches 30–50% of the gel, when the gelatin precipitates into grains and the gel is lost.
- Sets softer
- Acid below pH 4 — vinegar, fruit juice, wine.
Salt and acid are compensated for with more gelatin. Tannins from tea and red wine cloud the jelly by precipitating the gelatin itself.
How we know the rule holds
The source confirms itself three times on the same page, and that is what this calculator rests on.
The dose: its panna cotta holds 530 g of liquid — 30 g milk, 300 g cream, 200 g raspberry purée — and the table prints 4.3 g of gelatin. The rule of 0.8 g per 100 g gives 4.24 g: the book rounded its recipe up. What that pins down is what it counts as liquid — with the sugar in it would be 4.84 g, and with only the dairy, 2.64 g.
The Bloom formula: the printed example converts 2.6 g of Knox into 3.7 g of silver, and 2.6 × 225 ÷ 160 = 3.66. The printed substitutions for silver (1.1 g) and bronze (1.3 g) per 100 g of liquid come out of the same arithmetic, starting from the 0.8 g.
The fluid gel: the onion sauce takes 3.5 g of agar for 500 g of onion milk, and the recipe’s own scaling column prints 0.7% — which is where a fluid gel falls between the thick sauce and the purée of the instruction page.
Spherification stays out, and why
Sodium alginate and calcium chloride have not a single published dose anywhere on our shelf. Volume 1 of Modernist Cuisine names the technique and sends you to volume 4; the at-home volume does not cover spherification; McGee describes the mechanism without publishing a quantity.
The mechanism does have a source: alginate gels only in the presence of calcium. You make a calcium-free alginate solution of the flavour and colour you want, then drip or inject it into a calcium solution, where it gels on contact.
What is missing is the number, and a number without a source does not go on screen. When volume 4 reaches the shelf, this section becomes a calculator.
A note about the source
Our copy of *Modernist Cuisine at Home* is a scan with optical character recognition, and OCR gets names right while destroying numbers — ours turns “500 mL” into “S00 mL” in places.
So every dose on this page was checked against the image of the printed page, not the extracted text. The same check was repeated on the four brine recipes that already used this book: all four were correct.
Glossary
- Hydrocolloid#
- A long molecule that disperses in water and traps the liquid in a mesh, thickening or gelling it. Gelatin, agar, xanthan and carrageenan are all hydrocolloids; starch is one too, by a different route.Myhrvold & Bilet, cap. "Sauces" — "How to Make Gels and Fluid Gels" · McGee, cap. 11, "Plant Gums"
- Fluid gel#
- A gel that sets solid and is then blended back into a liquid. Thick on the spoon and thinning in the mouth, with a creamier texture than a sauce thickened with starch or xanthan.Myhrvold & Bilet, cap. "Sauces" — "How to Make Gels and Fluid Gels", cap. "Sauces" — "Onion Fluid Gel"
- Bloom strength#
- A measure of gelatin’s gelling power, named after Oscar Bloom, who invented the device that measures it. The higher the number, the firmer the gel for the same weight. Sheets sold as bronze, silver, gold and platinum correspond to rising Bloom ranges.Myhrvold & Bilet, cap. "Custards and Pies" — "Working with Gelatin" · McGee, cap. 11, "Jelly Consistency"
- Spherification#
- A technique built on alginate, extracted from brown seaweeds, which gels only in the presence of calcium. A calcium-free alginate solution is dripped or injected into a calcium solution and gels on contact, forming spheres or threads with a thin skin and a liquid centre.McGee, cap. 11, "Carrageenan, Alginates, Gellan"
Frequently asked questions
How many gelatin sheets equal one envelope of powder?
It depends on the grade of the sheet, which is why the conversion exists. The source’s formula is weight × the Bloom you have ÷ the Bloom the recipe calls for. A gold sheet (190–220 Bloom) weighs 2 g; a bronze one (125–155) weighs 3.3 g — and the two gel almost identically, because the weaker sheet is made heavier on purpose.
Can I swap gelatin for agar gram for gram?
No. Different doses and different behaviour: agar has to boil to hydrate, sets firmer and holds to 85 °C; gelatin melts at 37 °C, which is exactly what makes it dissolve in your mouth. For a demoulded gel the source uses 0.8% gelatin; for the vegetarian version of the same panna cotta, 0.15% agar with 0.12% xanthan.
Does xanthan gum gel?
No. It thickens: it gives the liquid body without letting it set, and it works cold, with no boiling. If you want a gel that comes out of a mould, that is gelatin, agar or carrageenan.
Why is there no spherification here?
Because no book on our shelf publishes a dose for sodium alginate or calcium chloride. McGee describes the mechanism and the glossary entry is here, but a number without a source does not go on screen — and that number lives in volume 4 of Modernist Cuisine, which we do not have.
What counts as “liquid”?
Whatever the source counts. In its panna cotta that is the milk, the cream and the fruit purée — 530 g in all — and the sugar and salt stay out. The 0.8% rule applied to those 530 g returns exactly the 4.3 g of gelatin the recipe prints.
Sources for this calculator
Every number comes from a single book, and the page says so. McGee is here for what he does better than anyone: explaining why salt, sugar and acid change the gel — without publishing how much, which he honestly does not have.
Modernist Cuisine at Home
Myhrvold & Bilet · The Cooking Lab
cap. "Custards and Pies" — "Raspberry Panna Cotta" · cap. "Sauces" — "How to Make Gels and Fluid Gels" · cap. "Sauces" — "Onion Fluid Gel" · cap. "Sauces" — "How to Make Full-Flavored Pan Gravy" · cap. "Custards and Pies" — "Working with Gelatin" · cap. "Custards and Pies" — "Firm Pastry Cream"
On Food and Cooking
McGee · Scribner
cap. 11, "Jelly Consistency" · cap. 11, "Carrageenan, Alginates, Gellan"