See my video of the results here: http://www.youtube.com/watch?v=emqUMFYsfIg
Introduction/Motivation: I just obtained a Pressure Whipper, and want to figure make an appealing beer foam for use in a variety of culinary situations. Several people online have posted various methods for making cocktail foams, and I found one person that attempted a bourbon barrel aged stout foam. The critical ingredients were: beer, egg whites, and sometimes gelatin. I varied the amounts of these ingredients for this lab.
Literature Review:
(unless otherwise cited, taken from the Science of Cooking by Harold McGee, covering any section that mentions gel, gelatin, and foam) (and no, that’s not an acceptable citation for any rigorous report, but being that I’m not getting any real credit for this, I figure that’s good enough).
Definitions:
Dispersion:
Dispersions are mixtures of two materials that are generally evenly mixed.
Gel:
Gels are liquids thickened with molecules. Unlike starch thickeners, however, gels are typically translucent due to the small size of the thickening molecules, either proteins or carbohydrates. These molecules don’t thicken and separate like starches tend to do, either. Gelatin molecules are proteins that expand with the addition of heat, and then bond to each other during cooling. They then set, or combine in a stable network of interlinked molecules, forming a gel.
Emulsion:
An emulsions is a liquid thickened with other liquid droplets (e.g. mayonnaise).
Suspension:
A suspension is solid dispersed into a liquid (e.g. coffee).
Foam:
A foam is a liquid thickened with air bubbles. Air bubbles disperse through the liquid and form a thickened, foamy product. The air in a foam interrupt the flow of water through the foam, allowing it to hold its form for some amount of time. Unlike gels and emulsions, foams are more effervescent and ‘live’ for a notoriously short amount of time. They tend to crumble under the force of their own weight in the presence of gravity. Gravity ultimately drains the liquid from the bubble walls, thinning the bubbles until then inevitably pop.
There are two main ways to delay the ‘popping’ or collapse of a foam. First, you can thicken the fluid with “truly substantial” [McGee, 595] particles or molecules (e.g. oil droplets, egg proteins) to physically slow the fluid drainage from the bubble walls. Second, you can add emulsifiers (e.g. egg-yolk lecithin) that can stabilize (i.e. strengthen) the bubble structure itself. However, it’s important to realize that foams are desirable because they are light and airy. Too much of a “substantial” addition or too much emulsification will negate the very purpose of a foam.
Foams are most simply stabilized by whipping air into the liquid. The addition of air to the liquid in the foam increases the surface area exposed to the air. This increases the ability of volatile aromatic compounds to release into the air producing, ideally, a delightful aroma.
Other ways of combining air bubbles with a liquid include foaming wands (i.e. what you get in an espresso foam) and the use of foaming devices that pressurize the liquid with CO2 or N2O.
No matter how you get the gas bubbles into the foam, if it is simply some gas and some liquid, you will create a very short lived foam (watch the lifetime of a latte foam to get some idea). The addition of emulsifiers (e.g. lecithin, protein) can extend the lifetime of the foam. Emulsifiers generally have a hydrophobic and hydrophilic segment. The hydrophilic segment extends into the water and water soluble portions of the foam, and the hydrophobic segment extends into the rest. By separating the two inherently insoluble portions of the liquid, emulsifiers prevent, or at least hinder, the inevitable mixing. The end result, to our delight, is a longer-lived foam.
Inevitably, however, any foam will eventually collapse due to the action of buoyancy. Even with sufficient emulsifiers, any air within a foam will float on top of any liquid, and and liquid will sink beneath the air in the bubbles. When the bubbles reach the top, they will dry and pop. When the liquid reaches the bottom, they will mix and form a gasless liquid.
Even yet, there are ways to delay this inevitable collapse. The addition of starches, pectins, gums, and even emulsified fats will slow this separation of the liquid from the gas. Generally, fat is a ‘foam killer’ [McGee, 639]. But, if the fat is emulsified (i.e. covered in egg yolk), the fat remains dispersed in the water phase, and the fat droplets are hindered in their ability to pop those delightful bubbles.
Foams can also use surfactants to elongate their lifetime. Surfactants reduce the surface tension of a liquid, which affects the amount of pressure that can build up in the air bubbles before they pop. [Kevin Liu]
Cocktail foams, like all foams, contain a dispersed phase (i.e. the bubbles) and a continuous phase (i.e. the liquid). Altering the composition and fraction of these two phases affects the final foam. Specifically, they affect the creaminess and viscosity of the foam. Creaminess can be achieved by creating many uniform bubbles of the dispersed gas. If the bubbles are all below 30 um in size, the tongue can no longer tell the difference and the foam takes on a creamy texture. Viscosity is affected by the dispersed phase bubble size and the viscosity of the continuous phase.
Agar-Agar:
A carbohydrate that acts like a gelatin protein. Agar (short for agar agar) is a mixture of several carbohydrates that are extracted from red algae. Agar solidifies at ~ 1% by weight, compared to gelatin which requires ~ 1% by weight for solidification. In general, agar is more crumble than gelatin, and sets around 110F/38C. However, agar won’t reliquify until it reaches 185F/85C (gelatin sets and reliquifies at the same temperature, ?F/?C.
Gelatin:
In the US, mostly manufactured from pigskin (and sometimes cattle skin and bones). The industrial process is very efficient at extraction, resulting in sheets or granules that are 85-90% gelatin, 8-15% water, 1-2% salts, and 1% glucose [McGee].
Both sheets and granules are soaked in cold water first so that the gelatin network can absorb the moisture and dissolve readily when warm liquid is added. If this cool liquid soaking is skipped, you could get gluey and clustering of individual or chunks of gelatin molecules [try this?].
Powdered gelatin can be used to make foams. Just use a 1:100 weight ratio for gelatin:liquid. Add these to a pressure whipper, and chill since the colder the foam the more stable it will be. Will it ever form a gel in the pressure whipper? [Kevin Liu]
Xanthan Gum:
Xanthan gum can be used at a 0.5:100 to 0.8:100 weight ratio. Just make sure to let it rest for at least 5 minutes in the whipping siphon. [Kevin Liu].
Background Research of RECIPES:
Dark and Foamy:
(http://www.youtube.com/watch?v=dWwQSkwSvKc)
The cocktail:
40ml Pampero White Rum
20ml lime juice
10ml simple syrup
4 dashes bitters
The foam:
1 can ginger beer
100ml Kraken Rum
dash of lime juice
gelling agents (cellulose powder and xantham gum) - proportions not specified!
The procedure:
1. Mix the cocktail
2. Put all the ingredients for the foam in a pressure whipper. Shake to mix. Add 2 packets of N2 (sic).
Barrell Roll - Beer, Foam, and Bourbon
by TWDIndustries, http://imgur.com/a/fUzFF
The cocktail:
Just a standard Old Fashioned
The foam:
4 egg whites
3 oz. lemon [he later suggests you use less lemon]
2 oz. simple syrup
1 oz. water
6 oz. of offgassed beer [he suggests stout, and later suggests more beer]
The procedure:
1. Add the foam ingredients to the whipper
2. Shake, add N2O, and let set for 1 minute. Add another N2O cartridge, shake for 1 minute.
3. Place in the refrigerator for 1 hour
4. Make the cocktail
5. In a chilled glass, ‘bottom’ the drink with the chilled foam.
6. Strain in the chilled drink.
NOTE: Kevin Liu recommends removing the lemon juice entirely, since the beer itself should have more than enough acidity to stabilize the foam. He recommends for pure beer foams 2xN2O and 1xCO2 cartridges.
Grand Marnier Cocktail Foam
(Kathy Casey, http://vimeo.com/channels/248411/34971663)
The cocktail:
Any. Suggests a Black and blue Cadillac Margarita.
The foam:
2 sheets gelatin
2 oz. fresh lemon juice
6 oz. simple syrup
4 oz. pasteurized egg whites [can be powdered, but not sure about the 4 oz. anymore]
3 oz. Grand Marnier
The procedure:
1. Bloom the gelatin sheets in ice water for 10 minutes
2. Combine lemon juice and simple syrup. Strain through a fine strainer into a saucepan.
3. Remove gelatin, squeeze out extra water and add to saucepan.
4. Heat over medium-high heat until gelatin just dissolves - immediately remove from heat. Do not let boil! Cool for 10 minutes on the counter.
5. Place egg whites in a bowl, then whisk in the cooled solution until incorporated.
6. Add to foam whipper and charge with 2 charges of N2O. Shake briefly in between charges.
7. Refrigerate for at least 4 hours, better if done overnight.
‘Guinness Foamed’ Beer:
(Kevin Liu, http://drinks.seriouseats.com/2013/07/cocktail-science-foam-eggwhite-gomme-dry-shake-beer-foam-eggwhite-alternatives.html)
drinks.seriouseats.com has a foam article that tells you to make any foam out of any beer with 1 or 2 charges of N2O and 1 charge of CO2 (with a ‘decarbonated’ beer). Interesting. The foam lasts for about 3 minutes and the foam started to melt away. A scant pinch of xanthan gum per 12 oz. of beer helps to stabilize the foam. The addition of the xanthan gum necessarily decarbonised the beer, therefore the CO2 charger is required to get a standard beer back out.
Experimental Design:
This lab examines the ingredients that go into a successful bear foam. We (myself and the friends and acquaintances I used as taste testers) define a successful beer foam as a foam, made primarily out of beer, that tastes like beer, that maintains a foam-like consistency for an appreciable amount of time, and is generally appetizing. We scoured the Internet for any recipe for a beer foam or cocktail foam (finding mostly cocktail foam recipes, and only one explicitly for a beer foam). These recipes included only a few necessary ingredients: beer, egg whites, and gelatin. Some had peripheral ingredients including simple syrup, water, lemon juice, and other gelling agents (including xantham gum and cellulose powder), but being a preliminary experiment we stuck with the basics. Our experimental procedure is outlined below:
1. 8 oz. beer plus 2 charges of N2O (hereafter called “simple”)
2. “simple” + 2 oz. egg whites
3. “simple” + 4 oz. egg whites
4. “simple” + 3 oz. egg whites + 1 sheet gelatin
5. “simple” + 3 oz. egg whites + 2 sheets gelatin
NOTE: The amount of beer is reduced by the amount of egg whites added to comply with the pressure whipper specifications (no more than 8 or 9 oz. of total liquid).
Methods/Procedure:
The procedure is simple, and is based primarily off of the Bourbon Barrel Foam Recipe of “TWDIndustries,” with the suggestion from Kevin Liu that lemon juice is not necessary since beer has enough acidity already. The procedure consists of:
1. Off gassing 6 - 8 oz. of your beer of choice (I chose Southern Tier 2XStout)
2. Adding the gelling/foaming ingredients. If gelatin is used, heat the beer so that the gelatin dissolves fully, then cool it to a temperature that will not cook the egg whites.
3. Add the beer solution to the Pressure Whipper, seal it, and add 2 charges of N2O gas (shaking briefly in between each addition).
4. Chill the Pressure Whipper for at least an hour, preferrably 4 hours (or even overnight).
5. Release, and record, the resultant beer foam.
6. Observe and record the general appearance (consistency, structure), observe how the beer foam collapses (do bubbles grow quickly? does the structure collapse in itself? how long does it take for ~ 2 cm of the original beer to form at the bottom of the glass), taste (does it still taste like beer? what is the mouthfeel? is is still appetizing?), and make general observations about the overall appeal of the resultant foam (i.e. will someone actually want to consume this? how long do they have before it collapses or becomes unappetizing?)
1. “simple”
|
Foam Lifetime:
less than one minute
Taste/Mouthfeel/Appeal:
like regular beer
What did it look like after it collapsed?
like regular beer
Overall rating/conclusion:
really not a foam at all, just a vigorously shaken beer
|
2. “simple”
+ 2 oz. egg whites
|
Foam Lifetime:
less than 5 minutes
Taste/Mouthfeel/Appeal:
very creamy initially
What did it look like after it collapsed?
rather gross, with networks of proteins
Overall rating/conclusion:
great for the first few minutes, then unappetizing
|
3. “simple” + 4 oz. egg whites
|
Foam Lifetime:
around 5 minutes
Taste/Mouthfeel/Appeal:
not much different from the 2 oz. egg whites
What did it look like after it collapsed?
very similar to the 2 oz. egg white foam
Overall rating/conclusion:
don’t really need 4 oz. egg whites for this foam
|
4. “simple” + 3 oz. egg whites
+ 1 sheet gelatin
+ chilled for 2 hours
|
Foam Lifetime:
almost 10 minutes before it started to really collapse
Taste/Mouthfeel/Appeal:
creamy, a little jello-like
What did it look like after it collapsed?
a little strange, it didn’t hold its structure very long
Overall rating/conclusion:
appealing and promising, if only it could last longer
|
5. “simple” + 3 oz. egg whites
+ 2 sheets gelatin
|
Foam Lifetime:
nearly 20 minutes before significant collapse
Taste/Mouthfeel/Appeal:
very much like jello, intriguing!
What did it look like after it collapsed?
the foam collapsed in a weird way, looked a little like brians
Overall rating/conclusion:
best yet! perhaps add egg yolk as emulsifier? or use Agar Agar?
|
Discussion & Conclusions:
It is clear that the egg whites are essential for any successful beer or cocktail foam. The egg proteins provide the backbone of the foam structure, and although we didn’t try a pure beer/gelatin foam, we are fairly confident that this would not produce an appealing foam (perhaps a beer gelatin?). Adding some egg-yolk instead of just egg-white may serve as an emuslifier which could extend the life of the foam and/or improve or preserve its desirable texture. However, adding a whole egg to 8 oz. of beer is likely to significantly change the taste of the foam. This is ultimately undesirable.
In all cases in our experimentation the beer foam didn’t keep its most appealing structure (a nearly frozen yogurt appearance, creamy texture, and tiny, uniform bubbles) for more than 5 minutes. It would be really nice (perhaps revolutionary?) if we could get the foam to maintain the texture and structure of a whipped cream (i.e. 30 minutes or more of smooth and appealing texture and appearance). This would allow the beer foam to be used as more of a mousse-like dessert or dessert topping, or even some addition to other foods (i.e. an IPA dip for french fries? a brown ale foam to top a stew? chocolate cake with a chocolate stout foam topping? just think about the possibilities!).
Our next steps are going to be examining the possibilities of adding some fat to the solution to reach the minimum 30% fat content required to create a whipped cream foam-type product. Generally, beer is free of fat, so the introduction of fat to the solution is likely to change the taste of the product. But if we used a strong, chocolate stout and was able to mimic, or at least approach, a chocolate mousse, we might be able to make this work.
In the meantime, I’m likely to try other beer styles with the 3 oz. egg white + 1 sheet of gelatin recipe. A bartending acquaintance has strongly recommended the use of Agar Agar instead of gelatin. There’s also the xantham gum and cellulose powder possibilites from the Dark and Foamy recipe, although since they didn’t specify the amounts we will have to conduct further experiments if we go down this path.
