Gelatin – few products are as ubiquitous in the kitchen yet so wrought with confusion and potential for misuse. Whether discussing gelatin in front of students who have had little or no exposure to it, or with seasoned pros who use it every day, I’ve come to realize that a lot of cooks see gelatin – as I did for many years – through a lens of vague, misleading, or just-plain-wrong information, however well-intended its source. Gelatin serves as a prime example of how subtle nuance with regard to ingredients and how we handle them can either lock us into a state of perpetual frustration or liberate us with better control, refinement, and creativity. What I will attempt to do here is quickly cover some of the basics gleaned from practical experience, some experimental testing, and a lot of technical reading. As with many aspects of cooking, there aren’t always hard and fast rules or optimal ways of doing things; there is always room here for personal preference. Hopefully with a bit of guided navigation through the complex world of gelatin others can benefit as I have, with a better informed launching point from which to make those choices and explore new territory…
SIX THINGS TO CONSIDER ABOUT GELATIN
1. The word gelatin has its roots in the Latin verb gelāre, to freeze, but eventually began to refer to any general transformation of a liquid into a solid - gelāta. It’s easy to see how it evolved over the years into terms we use today, such as congeal, helado, gelato, and specifically gelée and jelly. It’s believed that the earliest ancient forms of gelatin were not put to use in food per se, but rather as crude glues and adhesives. And though its culinary value became better understood and exploited over the centuries, the commercial gelatin we take for granted today did not begin to appear until the early 19th century. Indeed, most gelled dishes up to that point – savory and sweet – began with calves feet, much like this recipe for blancmange from the classic 1832 cookbook by Eliza Leslie, Seventy-Five Receipts for Pastry, Cakes, and Sweetmeats:
2. Gelatin is mostly protein, which is derived from collagen, which only comes from animal sources. It’s dry composition is roughly 87-92% protein, 7-12% water, and about 1% ash. The great majority of gelatin is produced from porcine (pork) or bovine (beef) sources – predominately from skins and hides, but also from bones (ossein). A lesser amount is derived from piscine sources (fish skin) – both cold and warm water species – and an even smaller quantity from avian (poultry) sources. Porcine gelatin still tends to dominate much of the worldwide production, especially in Europe, but elsewhere bovine gelatin is increasingly common; piscine and avian sources account for less than 2% of total production. The source of any given gelatin is important for those with dietary restrictions, but uncovering the source can be difficult. Package labeling can be frustratingly minimal, though a bit of internet searching can usually help. Lacking info directly from the manufacturer, we can make a few broad assumptions:
- If one sees ‘Kosher’ or ‘Halal’ labeling, one can assume it is of bovine origin (though I have seen some implausible internet rants that claim otherwise).
- If the gelatin is of European origin, there is good chance it is from a porcine source – strictly based on the numbers and the brands readily available to cooks.
- We can also use the two primary types of gelatin – A and B – in determining the source. Before the extraction process, all raw material for gelatin is treated with either an acid (Type A) or an alkaline (Type B). Most porcine sources undergo acid-treatment (A) and bovine sources with alkaline (B), though that isn’t absolute. Adding to the confusion, sometimes ‘Type A’ is used to imply ‘food grade’, but from a manufacturing perspective, both A and B types can be food grade. Labeling by type is not necessarily definitive of overall quality – beyond this initial acid/alkaline pre-treatment, the production of both types are generally the same, though the properties of Type A and B gelatin can differ slightly in the final product.
- Gelatin can be of mixed sources, as is the case with the widely available Knox brand – its parent company Kraft states that it is a blend of both porcine and/or bovine sources.
- For those looking to bypass mammalian sources altogether, gelatin from warm-water fish - sometimes referred to as isinglass – can approximate the properties of bovine and porcine of similar strength, though its setting and melting temperatures are generally lower, by a difference of up to 5°C/9°F. Cold-water species of fish gelatins form very weak gels by comparison and on the whole are not considered commercially viable.
- Though perhaps obvious to most, anything labeled ‘vegetable gelatin’ is not made from collagen, but rather one or likely a blend of plant-based hydrocolloids aiming to replicate the unique properties of gelatin.
3. The most common identifier of gelatin is by its ‘strength’ – a grading system known as the ‘Bloom Scale’. This rating is named for Oscar Bloom, inventor of the gelometer patented in 1925 – an instrument that measured the amount of force needed to deform a gel to a specified degree. Though adapted over time, the same basic mechanism is still used as an industry standard in measuring gel strength: a 6.67% solution of gelatin in water is heated and set at specific temperatures for specific periods of time. The resulting gel is pressed with a cylindrical plunger to a depth of 4mm – and that force, measured in grams, is its Bloom rating. Thus, a gelatin whose tested gel requires 200 grams of force has a strength of 200 Bloom. All commercial gelatin lies within a range of 50 to 300 Bloom, however the range accessible to most cooks is generally narrowed from 125 to 250.
A higher Bloom value generally represents a stronger gel, a higher gelling temperature, a lighter color, and neutral odor/taste – but Bloom strength is not necessarily a complete means of determining a gelatin’s specific properties or purity. But overall quality is also a function of the extraction stage from which the the base gelatin is produced – early extractions of the raw material tend to have higher Bloom ratings than subsequent extractions – which number from three to six – requiring increasing amounts of heat and water to access the remaining protein. I like to think of it like olive oil – the first pressings at lowest temperatures offer the highest quality.
Regrettably, as with animal source, most retail gelatin labeling omits this very important Bloom number. In its place we see instead a grading system using the names of precious metals (bronze, silver, gold, and platinum) in designating gelatin sheets of different strengths (more on this below). The aforementioned Knox powder does not list a Bloom number on its packaging, however my inquiry to Kraft revealed a ‘target’ Bloom strength of 235 (most sources list it as 225 – close enough – so I will stick to that ’rounded’ figure).
Before moving further – the use of the word ‘bloom’ can be confusing as it is used to refer to two things – a gelatin’s strength, and the initial process of hydrating or soaking in water.
4. Although sheet gelatin of different grades have different weights and different bloom strengths, they are theoretically interchangeable.
To quote Schrieber and Gareis (Gelatine Handbook):
In the case of leaf gelatine, the leaf thickness and hence the weight of the individual leaves is set according to the type of gelatine being processed. Thus, any particular leaf of gelatine dissolved in a given amount of fluid results in the same gelling power, independent of whether ‘‘high-Bloom’’ or ‘‘low-Bloom’’ gelatine is used in the leaf manufacturing process. This principle is valid for both major worldwide manufacturers and hence for all the brands available on the market.
The table below offers an average Bloom strength for each grade of sheet gelatin, its weight, and number of sheets in 1000g, alongside a common 225 Bloom powdered gelatin:
The grade differentiates the gelling ability on a per gram basis, so bronze gelatin actually weighs more than gold yet achieves the same “set”. For example, in a recipe calling for 2 sheets of silver gelatin, the same gel strength should be achieved by substituting 2 sheets of either bronze or gold grades. Recipes that call for a weight of sheet gelatin without also stating the Bloom strength can cause obvious confusion, as the weight of each sheet changes with an increase in Bloom strength. In such situations, while we might assume a silver grade will produce the desired result, it is often best to prepare small test batches in order to fine tune the formula.
Converting between sheets and powdered gelatin can be more problematic. Several sources cite the powdered gelatin equivalent of one sheet to be approximately 1 teaspoon; however, volume measurements are not as consistently accurate as measuring by weight, and as we can assume from the table above, 2.3g of 225 Bloom powdered gelatin would most certainly result in a stronger gel than one sheet or 2g of 200 Bloom gold grade gelatin.
The following conversion formula allows us to use the figures above to more accurately move back and forth between different gelatin grades, or between sheet and powdered gelatin:
The weight of the known gelatin x square root (known gelatin bloom strength/unknown gelatin bloom strength) = weight of unknown gelatin.
For example, a formula calls for 2 sheets of silver grade gelatin (160 Bloom). At 2.5g per sheet, the total weight of the known gelatin is 5g. To substitute powdered gelatin in place of the silver grade sheets:
Weight of known gelatin = 5g
Bloom strength of known gelatin = 160 (silver)
Bloom strength of unknown gelatin weight = 225 (powdered)
160 divided by 225 = 0.71
The square root of 0.71 = 0.84
Multiplying our known weight of silver gelatin by a factor of 0.84 will give us our equivalent weight of powdered gelatin.
5 x 0.84 = 4.2
Thus, 4.2g of 225 Bloom powdered gelatin has the same gelling strength as 2 sheets or 5g of 160 Bloom silver gelatin, or for every sheet of silver, substitute 2.1g of powdered gelatin.
Or you can save time and use the table below, which calculates this basic formula for substituting between different Bloom strengths by weight from commonly used 140 to 225 Bloom:
So, given all these options, which gelatin is ‘better’? Some feel that powder is somehow less ‘pure’ than sheets (in reality, all sheets are made from powdered gelatin). Some prefer the convenience of counting sheets over weighing of powder. Some use a specific gelatin for different applications. Some choose based on price (though for a true comparison, it’s best to compare the price per sheet between, say, silver and gold – a 1K box of silver may be cheaper overall, but remember that there are a hundred more sheets in that box of gold). And then some are limited by what is available from their local purveyors, though I’d argue that should no longer be an obstacle to sourcing anything in the age of internet.
5. Gelatin will absorb a fairly constant amount of water – about five times its own weight. So why do we tend to use large amounts of excess water for hydration? For example, one sheet of silver gelatin that weighs 2.5g will absorb about 10 to 12g of water. Because it can be difficult for such a small amount of water to cover the surface area of one gelatin sheet, it makes sense to hydrate the gelatin in a larger amount of water to completely submerge the sheets, and then gently squeeze out any excess water. This practice is perfectly acceptable, though care must be taken in handling the gelatin so that it loses none of its gelling power in the process; common loss can occur when the gelatin breaks into smaller pieces, is hydrated in warm water, or when it is squeezed with warm hands.
Ideally gelatin sheets are bloomed in just enough ice water to cover, followed by draining through a sieve with gentle pressure to remove excess water. Excess water that is added to a recipe along with the gelatin will in effect dilute its gelling power. As a measure towards consistency, I have always preferred hydrate gelatin in a measured amount of water (about 5x) for 10-15 minutes and simply add any excess with the gelatin, having accounted for the water within the recipe. A third method employed by some chefs (and one that I’m playing around with) is to prepare a ‘gelatin mass’ in bulk by hydrating a large amount of gelatin in a precise measurement of water and heating the whole until the gelatin is dissolved; this is further allowed to set, and these chefs’ recipes will then call for a measured weight of the set gelatin mass rather than a number of sheets. Converting recipes that use gelatin mass – and I see more and more of them – can be a pain if the variable includes gelatin of unknown Bloom strength.
Powdered gelatin is hydrated in a similar manner; the gelatin is sprinkled over a small bowl containing 5-10 times its weight of cold water. Sprinkling the gelatin on top of the water will allow it to disperse and absorb water at an even rate – pouring the water over the gelatin will often result in lumps of dry granules that lose access to the water because the surrounding gelatin swells in size as water is absorbed. It is common practice to use water when hydrating either powdered or sheet gelatin, but most liquids are acceptable, as long as they are cold. When converting between sheets and powder, it is important to know that gelatin absorbs about five times its weight in water. That is, 5g of gelatin will absorb 25g of water. While this water is always listed in formulas using powdered gelatin, it is not listed in formulas where sheets are placed in excess water. This difference in water should be considered when converting between sheets and powder.
A couple more general reference points on the behavior of gelatin gels:
- In typical dosages, gelatin begins setting in the range of 15-20°C/60-70°F and melts at just about body temperature, 35°C/95°F. This narrow gap between setting and melting is referred to as hysteresis. Though visible signs of gelling occur rather quickly under refrigeration, it’s important to realize that the complete gel structure and thus full strength may take up to 12 hours to set.
- Excess heat over extended periods of time can damage gelatin and produce a weaker gel; ideally, gelatin should never exceed temperatures 60°C/140°F.
6. Consider how other ingredients affect gel properties. Let’s take a step back to remember that gelatin is a hydrocolloid – it gels water. Although we set complex mixtures that also contain fats, sugars, and other ingredients, we should be mindful in determining gelatin dosage based on water content. For example, In setting a creme anglaise into a simple cremeux, we should look first at the weight of water, excluding the fat and nonfat solids; further fine-tuning of the gelatin ratio can then be done as one assess how these other factors may affect the gel’s properties, if at all.
A very worthwhile exercise is to set a range of plain water gels of various gelatin types and concentrations – it’s a valuable exercise to try with all hydrocolloids – one can learn a lot about the subtle differences in products before other factors like fat, solutes, and pH are introduced…
Factors that can affect the properties of gelatin:
- High levels of dissolved sugars or salt can slow the hydration and dissolution of gelatin; because they bind water, the gelatin must compete for available water. However, sucrose and sugar alcohols like sorbitol help stabilize gelatin gels, increasing both the setting time and the melting temperature.
- Fats can soften or ‘plasticize’ gels, which may require a higher dosage of gelatin. On the other hand, similar items that contain solid fats like cocoa butter may require a lower dosage of gelatin, as those fats provide structure of their own.
- Gelatin is stable within a pH range of 5-9 – increasing the acidity can weaken gel strength. For gels with a lower pH, one can simply add more gelatin to compensate, or use a buffering salt such as sodium citrate at roughly 1% of the weight of gelatin.
- Some fruits – such as pineapple, papaya, kiwi, and fig – contain proteolytic enzymes (papain, bromelain) that inhibit proper gelling; using these fruits with gelatin requires prior heating to destroy these enzymes.
- Alcohol will also inhibit gel formation and requires higher concentrations of gelatin to achieve gels comparable to water alone. An intriguing formula and good starting point, for edible cocktails proposed by Martin Lersch of khymos.org: % gelatin to add = (% alcohol in final mix x 0.1) + 2
- The synergistic effects of gelatin combined with other hydrocolloids are many; perhaps the best overview of gelling possibilities can be found in Volume Four of Modernist Cuisine.
I think that sets us up for some more in-depth topics in the future, as this only begins to scratch at the surface of gelatin. Below, of many variations of gummy candy that I’ve tried, my current favorite – adapted from a formula taught by Jean-Marie Auboine:
Passion Fruit Gummy Candy – Opusculum
Some invaluable references below on the subject of gelatin:
Gelatine Handbook: Theory and Industrial Practice, by Reinhard Schrieber and Herbert Gareis 2007
Handbook of Food Proteins, edited by G.O. Phillips, P.A. Williams 2011
Handbook of Hydrocolloids, edited by G. O. Phillips and P. A. Williams 2000
Modernist Cuisine, by Nathan Myhrvold, Chris Young, and Maxime Bilet 2011
How Baking Works, 2nd Edition, by Paula Figoni 2010
Gelatin Handbook,Gelatin Manufacturers Institute of America 2012
And did you know that Kitchen Arts and Letters in NYC now sells books online? Awesome!