posted by Dave Arnold
Anyone with a packet of agar and a whisk can clarify fragile fresh juices, or anything else for that matter, in under an hour with zero pieces of special equipment. The yield on the technique is high—as good as gelatin clarification. Read more for details.
Yesterday I wrote a post about a new clarification technique posted by Ideas in Food where agar gels are put in vacuum bags to get clarified liquids out of them. They call the technique “compression clarification.” I stayed up till 1am or so getting the post out, vegged for a bit, and tried to go to bed. I could not sleep. Something was gnawing at me. I kept thinking about how much harder the Ideas in Food block of agar looked in the bag as opposed to mine. Mine was so soft it broke just by moving it and was quite soupy in the bag. I used the same 2 grams of Telephone brand Agar per kilo of product that I always use, which is just barely gelled. I wondered why theirs looked so much harder.
Something else bothered me: I don’t like the term compression the way it is used by chefs. I don’t like it for the same reason I don’t like the Under Pressure title of Thomas Keller’s sous-vide book. The terms are misleading (unless Under Pressure is a pun on under-pressure, meaning less pressure than normal, in which case the title is hilarious). With the exception of items that contain air, foods in vacuum bags aren’t being compressed (except at the edge where the bag tries to press together). Instead, vacuum bags press against your food with exactly the same force that air was pressing against it before. Only if your food has a lot of air holes that get evacuated during the vacuum cycle will it feel a lot of pressure. Air holes will feel a force of about 15 psi because you have removed that much pressure from them, sealed them inside the bag and then brought the force of the atmosphere back to bear on them. Even flash infusion isn’t compression, it is injection. Many things with air in them, a block of aluminum foam for example, won’t compress in a vacuum bag either (although it will be under compression), because they are too strong.
Agar gels, if well made, don’t have air. They are essentially liquids with some solids mixed in, and are uncompressible.
Also, I had been using physical techniques to clarify with agar for quite some time: see my experiments with spin gel clarification. Something I had forgotten was that I could get clarified juice out of those gels even after they were broken. I had dumped out one of the gels and spun it again, and even though the gel had been broken, I got more clarified juice. The reason I didn’t develop that technique further was it required a centrifuge.
All of a sudden it hit me like a ton of bricks: not only do you not need the centrifuge, you don’t need the bag and you don’t need the vacuum. All the bag was doing was slapping the agar silly. I could do that with a whisk! It was 3am. I jumped out of bed trying not to wake my wife, got dressed, jumped on my bike and dashed off to The FCI to get agar, OJ, and cheesecloth. I wanted lime juice, but at 0 dark 30 in the morning I didn’t want to squeeze any limes. OJ was fine.
Well, it worked like a champ. I made it home bout 3:45, clarified the juice, shot the pictures, and was in bed by 5. I slept like a baby—till 7 when I had to get up with the kids.
The advantages of this technique are:
- It is fast so fragile juices like lime can be clarified
- You need no special equipment
- It is vegetarian
- It is foolproof
- The results are clearer than gelatin for some products
- You don’t tie up fridge space with hotel pans
- You don’t tie up freezer space with hotel pans
- Yield is high
- Because there’s no freezing involved, you can clarify alcohol without liquid nitrogen (I’m letting the cat out of the bag—that was supposed to be my next post)
- Agar needs to boil to hydrate. Don’t boil heat-sensitive juices like lime. Instead use 4 parts room temp (25°C) juice and hydrate in 1 part water. After the juice is added to the boiling agar-water mix (off the heat) the temperature will be perfect. If you are using refrigerated juice that can tolerate some heat, boil 1 part liquid with the agar and add in 2 parts refrigerated juice.
- Use real cheesecloth. Don’t use the stuff from the supermarket with the picture of the turkey on the package. That stuff is ludicrous. I don’t know why they make it. If you can’t get real cheesecloth use muslin, a large cloth napkin, or a smooth-finished dish towel.
1.) Measure out 500 grams cold OJ, 250 grams cold OJ, and 1.5 grams of Telephone brand Agar (0.2% of total juice weight). 2.) Whisk the agar into the 250 grams of cold juice to disperse the agar then heat to a boil while stirring and allow to simmer a couple of minutes to hydrate the agar. 3.) While briskly whisking the boiling-hot agar solution add the 500 grams of cold juice in a thin stream. Don’t allow the mix to drop below 35°C or pre-gelling could ruin your result. 4.) Put on an ice bath to set.
5.) Using a whisk, gently break up and stir the gel into agar “curds.” 6.) Dump the curds into a cheesecloth lined chinois. 7.) Lift and gently squeeze to drain. 8.) After a while you can dump the curds back into the bowl to break them up some more.
9.) Alternatively, you can just stir the curds in the cheesecloth to release more juice. 10.) Twisting the cloth presses juice out gently and quickly. Don’t twist too hard or you will extrude the agar through the cheesecloth. 11.) The clarified juice. 516.8 grams! And I started with unstrained juice! If there are any agar particles in the juice, filter it through a coffee filter. 12.) The leftovers. 87.7 grams. Yeah I know the numbers don’t add up to 750 grams.