A little more than a week ago Dave Arnold posted a great, new technique: pressure infusion using a conventional iSi whipper! Just think of it – the whipper has been around for decades, and years a go Ferran Adrià pioneered it’s use for espumas. Several have suggested it’s use for carbonation of fruit. But no one had thought of utilizing the whipper for infusions – until August 11th when Dave Arnold of Cooking issues posted the results of his experiments in “Infusion Profusion: Game-Changing Fast ‘N Cheap Technique”. The first blogger to pick up the technique and post about it on August 12th was Linda of playing with fire and water who termed it a revolutionary technique. A couple of days later, on August 17th Aki and Alex of Ideas in food posted a combined pressurized infusion of basil and marination of mozzarella. And then on August 20th James of Jim Seven describes his results comparing conventional cold brewed coffee to cold pressure brewed coffee. It’s really fascinating how fast the idea spread, and it illustrates the benefits of an open and sharing approach to food innovations.

The science behind this is quite simple: in the pressurized canister nitrous oxide (N₂O) dissolves and penetrates the food. When the pressures is suddently released (and it is important to release pressure as fast as possible) the sudden pressure drop causes the dissolved gas to nucleate and form bubbles which expand and disrupt cells, thereby releasing flavor compounds. The physical phenomenon is known as cavitation.

A single N₂O charger contains 8 g of gas corresponding to 0.1818 moles or a volume of 4.1 L at 25 °C and 1 atm pressure. The volume of the chargers is 0.01 L which gives an impressive initial pressure in the chargers of 445 atm! With an approximate volume of 0.7 L the pressure in an empty whipper charged with a single charge would be nearly 6 atm. When liquids are added the volume decreases, but the effect on the head pressure will depend on the type of liquid added. The solubility of N₂O in water is 0.15 g/100 mL at 15 °C, meaning that with 100 mL of water, the head pressure would be roughly 10% higher than in an empty canister (that is, if the solubility is independent of pressure – I’m not quite sure about this). However, since N₂O is a rather non-polar molecule the solubility in ethanol or even oils is much greater than in water, with a resulting lower head pressure. But since flavor delivery is mediated by the dissolved gas suddenly nucleating and bursting cell structures, infusions using ethanol or oil will actually be more effective than those with water because more gas can be dissolved in these solvents (besides the fact that ethanol and oil are better solvents for flavors than water).

Thinking about how I could utilize the pressure infusion technique I came to think about the problems I ran into with hay like off flavors in the parsley and banana flavored marshmallows I made for TGRWT #2. The off flavors can be traced back to 3-methyl-2,4-nonanedione which likely stems from oxidation of unsaturated fatty acids or polyenes. Crushing parsley inevitably leads to oxidation (possibly also enhanced by mixing intra and extra cellular comounds/enzymes), but with pressure infusion – practically in the absence of air – seems to be much gentler than crushing according to Dave’s initial report (as judged by color). So I did a quick experiment with this, infusing a couple of sprigs in 2 dL of water for about 2 minutes. This was by no means enough, and the water had only a faint aroma of parsley (vodka would of course have been much better for the flavor extraction). But it was a clean parsley aroma, and the water was perfectly clear.

An updated version of “Texture – A hydrocolloid recipe collection” is now available for download (version 2.3). The longer I work on this, the more I realize that it will never really “finish” – there’s always more to add. And believe me – my todo list is still quite long (and I even have some feedback which I haven’t had time to incorporate yet). But I thought that since it’s more than a year since the last update, it was about time to share with you the things that have been changed. Major changes and updates include:

Pictures: This is the biggest visual change! Some recipes are now equipped with pictures which may give you an idea of the texture AND they indicate that the recipe has indeed been tested. But I need your help to add more pictures to the recipe collection (please follow the link to read more about how you can contribute pictures)! And of course - a big thanks to those of you who have already contributed your pictures!

Recipes: Recipes have been added and the total number is about 310 now. I’m getting a little more picky now with regards to which recipes I add. Ideally each new recipe added now should illustrate something new.

I should mention that I’m very grateful for feedback from readers and users of this recipe collection. Thank you very much with helping me improve the document! If you find typos, wish to comment on something or have suggestions on how to improve the collection, please do not hesitate to write me an email at webmaster (at) khymos (.) org or just write a comment in the field below.

Please head over to the download page for the links.

An updated version of “Texture – A hydrocolloid recipe collection” is now available for download (version 2.2). There are two file sizes available: screen resolution (~1 MB) and high resolution for printing (~5 MB). Some recipes have been added bringing the total number up to about 270 recipes. Apart from this the version includes corrections of typos and updates of indexes and the supplier list. There is a new index for alcoholic preparations plus a small glossary. Again I should mention that I’m very grateful for feedback from readers and users of this recipe collection. Thank you very much with helping me improve the document! If you find typos, wish to comment on something or have suggestions on how to improve the collection, please do not hesitate to write me an email at webmaster (at) khymos (.) org or just write a comment in the field below.

For the food blogging event They Go Really Well Together (TGRWT #1) I decided to used baked garlic. Baking gives garlic a slightly sweet, mellow taste and I figured this might work well with the soft texture of an espuma. Just make sure you get fresh garlic without green sprouts – they will give a bitter taste.

4 cloves of baked garlic (baked whole, 30 min @ 150 °C)
3.5 dL strong coffee
30 g sugar
40 g chocolate (70% cocoa)
ground cardamom
3.4 g gelatin (= 2 sheets)
1.5 dL heavy cream (38% fat)
1 iSi cream charger

Mix garlic cloves and coffee with blender or hand-held mixer. Add chocolate, a pinch of cardamom and heat while dissolving sugar. Stir in pre-soaked gelatin. Cool, add heavy cream, sift through fine mesh to remove remaining pieces of garlic and fill 0.5 L iSi gourmet whipper. Charge with 1 cream charger and leave in fridge over night. Serve with a drizzle of instant coffee.

How it tastes? In the finished espuma served cold, the first aroma noticed is coffee accompanied by a sweet taste on the tongue. This is followed by a faint chocolate aroma which then gives way for an aftertaste dominated by garlic. It’s quite surprising and the aromas blend well together. I used 30 g of chocolate, but I’ve increased it to 40 g in the recipe since the cocolate aroma was a little weak. As for uses, I think it would go well with a steak for instance. If used as a dessert I would perhaps reduce the amount of garlic to 2 or 3 cloves so as not to overwhelm the guests (unless they frequent the restaurant Garlic & shots in Soho, London where even the beer is served with garlic!).

In a comment to my post on making carbonated fruit the iSi way, JoJo at eat2love made me aware of a company, FizzyFruit, that actually sells carbonated fruit in pressurized containers. The fruits currently available are grapes, honeydew and cantaloupe. Turns out that their homepage features some recipes by – surprise, surprise – Homaru Cantu! Here are some of the recipes:

Proscuitto and melon
150 g carbonated melon
12 slices proscuitto ham
1 dL balsamic vinegar, frozen, shaved to snow
salt
olive oil

Wrap melon pieces with proscuitto, season with salt and drizzle with olive oil. Scatter balsamic “snow” over the top just before serving.

Champagne and Crab
150 g carbonated grapes
350 g picked crabmeat
1/4 bunch of chives, chopped
1 diced shallot
1 orange, juiced and zested
1/2 dL mayonnaise
1/2 dL fennel, shaved thinly
salt

Toss crab with shallot, fennel, mayonnaise and orange juice/zest. Season with salt and leave in refridgerator for 1 hour. Add carbonated grapes, toss with crab mixture and chives. Serve immediately.

Orange Sangria
2 L fresh squeezed orange juice
150 g carbonated fruit (grapes, melon)
8 sprigs of crushed mint
5 dL of crushed ice

Combine ice, orange juice and mint. Add carbonated fruit and serve immediately.

Fresh Fruit Trifle
150 g carbonated fruit (grapes, melon)
2.5 dL fresh whipped cream
1/2 vanilla bean scraped

Add vanilla bean scrapings to cream and whip until stiff peaks are formed. Layer carbonated fruit with whipped cream and serve immediately.

Ants on a Log
150 g carbonated grapes
2.5 dL of chunky peanut butter
4 long ribs of celery

Rinse and dry celery. Fill celery with peanut butter. Stud the celery with the carbonated grapes. Serve immediately.

(The recipes were made generic and converted to metric units)

Based on some googling of espuma and foam recipes (including Ferran Adria’s coffee espuma), I figured that the following should work:

2 dL coffee
2 sheets of gelatine
3 dL heavy cream
sugar/vanilla sugar

Soak gelatine in cold water. Strain. Dissolve gelatin sheets in the hot coffee and stir in sugar while heating. Cool. Add heavy cream. Filter through a fine meshed sift (just in case there should be any undissolved sugar, gelatin or particles) into a 0.5 L iSi gourmet whipper. Screw on top and charge with a cream charger. Shake 2-3 times and leave in fridge for a couple of hours. Hold whipper upside down, shake once to displace mixture towards the nozzle in case it is stuck and dispense. Texture is soft and silky. Tastes delicious!

Some more chemistry: The cream chargers contain dinitrogen oxide (N₂O) which is less polar than carbon dioxide (CO₂), and hence more soluble in fat (such as heavy cream for instance). Another reason why carbon dioxide is not used in this recipe is probably that when it dissolves, some carbonic acid is formed which could curdle milk based products if pH drops to much and also influence taste (but carbonated milk has actually been marketed!). The idea of using dinitrogen oxide for soda/beer has also been explored.

The instruction booklet which comes with the iSi Gourmet Whipper only mentions cream chargers (filled with N₂O, dinitrogen oxide), whereas soda chargers (filled with CO₂, carbon dioxide) are not mentioned (I guess the opposite is true for the iSi Siphons?). This is quite amazing actually! Luckily however the cream and soda chargers are exactly the same size and both hold 8 g of gas. So it should be possible to make carbonated fruit with any of the iSi whippers (cream, easy, gourmet, dessert, thermo) or siphons available.

Here’s how you proceed:

1. Fill you iSi whipper (or siphon) with fruit, preferably fruit which has a cut, wet surface to allow the carbon dioxide to dissolve in the water/juice.
2. Screw on top securly
3. Charge with one soda charger (two if you have the 1 L whipper)
4. Leave in fridge over night
5. Release pressure with valve (Important!)
6. Unscrew top and serve immediately!
7. Enjoy!

This is what carbonated grapes look like. As you see, I decided to cut the grapes in to halves.


Notice how they sizzle!

A quick recap of the chemistry: cold water dissolves more CO₂ than tempered water, that’s why we leave it in the fridge. Also, remember that it takes some time for the carbon dioxide to dissolve in water, therefore it’s better not to be in a hurry. A quick calculation of the pressures gives the following: Both gases have molecular weights of 44 g/mol, so 8 g of gas corresponds to 0.1818 moles or 4.1 L at 25 °C and 1 atm pressure. The volume of the chargers is 0.01 L which gives an initial pressure in the chargers of impressive 445 atm! With an approximate volume of 0.7 L this gives a pressure (in an empty whipper) of nearly 6 atm – the same as in a bottle of champagne. However once you add water, the equilibriums will change and the pressure in the head space will drop. Anyone who remembers how to calculate the head space pressure at equilibrium if the container is filled with 0.5 L of water and cooled to 4 °C?

I’ve done some googling and there is also some mention of making carbonated fruit with an iSi whipper over at Ideas in food.

(The word play in the title works better for those with a mother tongue where iSi would be pronounced just like “easy”!)

The invention has been commented on thoroughly in the blogosphere. See for instance Skillet Doux and Movable Feast – both feature some nice close-up pictures of espesso (including the one above).

Espesso has been available in Europe since 2002 (anyone know where?), but was just recently introduced in the US. Appearantly, the foam is served warm in Europe, but has been served cold in Chicago, at Lavazza’s three locations there.

According to the reports, espesso is made from espresso and a “secret” ingredient. The ingredients are mixed and left to settle for 12 hours under pressure. The product is then dispensed from the iSi Gourmet Whip (more info here, the propellant gas is nitrous oxide, N₂O). As a chemist I certainly wonder what the “secret” ingredient is? If it is true that espesso has been served both warm and cold, they would need to use a thickening agent which is not very sensitive to temperature. Also, it appears that the foam once served is not stable for more than a couple of minutes.

My best guess would be xanthan and guar gum, or possibly a combination of the two. These hydrocolloids show thixotropic properties – when subjected to pressure/agitaion they soften, but then they jellify again afterwards. In other words – they could be easily dispensed through a siphon and would then solidify in the cup. Also, xanthan and guar gum are relatively temperature independent with regard to their thickening properties. Check out the INICON manuals on texture for great (and FREE!) information on these and several other hydrocolloids.

Update: The Lavazza homepage now features a video and a tool to find your nearest Espesso!