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Matt's Food Blog

Gelatin Conversion Confusion

My friend Tom’s birthday looms, and to celebrate he’s organising a soirée. We’ll be cooking for about 12, more of that anon. One of the dishes I’m keen to try is from Brent Savage’s Bentley book. I’ve had it for a while and despite lots of great sounding stuff contained therein, I haven’t actually tried any of the recipes. I’ve long been tempted by the exquisite sounding ‘Smoked Eel Parfait with White Soy Dressing and Seaweed'; not only because of how I imagine it tastes: also on account of how cool the dish looks. The eel parfait is set in a cylinder shape, then wrapped in a thin film of celery jelly – looks like a liquorice allsort.

So I have my smoked eel – courtesy of Sawyers in Belfast (Lough Neagh smoked eel is a big deal it turns out – though most of it is exported – see here and here for interesting articles). I’ve also ordered some new carrageenans from Cream Supplies – who do a range of modernist ingredients. So really all to do was to get going with practicing the recipe – that’s where I hit the snag.

The book calls for two sheets of titanium strength gelatin. Well – I only have platinum strength, and it turns out that finding out how to convert leaf gelatin amounts according to class is more tricky to work out than I would have thought.

Gelatin strength is measured by bloom – the higher the bloom value the greater the gelling strength (or the less gelatin required to set the same amount of liquid). Gelatin leaves (or sheets) are sold classed as titanium, bronze, silver, gold and platinum. Additionally different leaves have different weights, and different manufacturers use slightly different bloom strengths. So to convert a recipe that calls for a certain number of sheets of gelatin of a certain type for use with another type of gelatin you need to know: 1) the weight per leaf of each type of gelatin, 2) the bloom strength of each type and lastly, a conversion formula. You will by now appreciate that this takes a little effort to work out.

Cue the fabulous Texture – A Hydrocolloid Recipe Collection which is put together by Martin Lersch at his Kymos blog, which has amongst it’s extremely informative pages a chart of gelatin leaves, the range of their bloom strengths, and a conversion formula. Unfortunately titanium strength gelatin is not included, though most sources that I can find suggest it’s around 100 bloom.

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Here’s the formula suggested in Texture: $Mass B = \ Mass A (\frac{Bloom Strength A}{Bloom Strength B})$, where Mass B refers to the mass of the leaves you have, Mass A to that of the leaves in the recipe, and similarly Bloom Strength B refers to the bloom strength of the leaves you’re using etc.

Some sites suggest applying a square root to the fraction: $Mass B = \ Mass A \sqrt(\frac{Bloom Strength A}{Bloom Strength B})$ however Martin Lersch suggests the former works better for the bloom strengths he supplies. So putting it together is a bit of a hotchpotch, I’ll go with his initially as he’s clearly a legend given how comprehensive Texture is (see below for a table of info re different bloom strengths etc).

The smoked eel parfait recipe calls for two sheets of titanium strength gelatin, which earlier in the book he explains weigh 5 grams each. So putting all that together using our formula and the table below suggests the weight of platinum gelatin we need is $\ 10(\frac{100}{240})$ which is 4.2, and as the platinumn sheets weigh 1.7 grams that means we need 2.5 sheets: easy!

Leaf TypeBloom StrengthGrams/leaf
Titanium1005
Bronze125-1553.3
Silver1602.5
Gold190-2202.0
Platinum135-2651.7