Introduction: The Best Sweet Pea Sorbet on Earth (and Some Science on Ice Creams and Flavors)
I recently got myself a centrifuge to use in the kitchen and was playing around one day with peas. I threw them in a blender, threw the puree in the centrifuge, and when it had come out, the peas had separated into three layers. There was the bottom layer largely composed of the starchy pea solids, the top layer that was the liquid from the peas combined with the water-soluble sugars and chemicals lending to the flavor of the peas, and in the middle was a thin layer we in the culinary world call "pea butter." I got to thinking one day about what I could use these layers for and, for the top layer, I decided to make a sorbet. Here is my absurd method for making a pea sorbet using a centrifuge, an immersion circulator, enzymes, a stabilizer, and some liquid nitrogen.
This is an entry in the
Science of Cooking
Step 1: Gather Your Equipment and Ingredients
The equipment necessary for this little project is as follows:
1 immersion circulator
1 container for the water bath
1 large plastic bag (ziploc or vacuum bag)
1 refractometer for measuring sugar content
1 centrifuge (I use the Waverly CL4M)
Centrifuge tubes (minimum of 8 50ml tubes recommended)
1 squeeze bottle to assist with filling tubes
1 scale for ingredient measurement
1 scale that can weigh to the tenth or hundredth of a gram for weighing the stabilizer and puree
1 coffee filter
1 mixer (I prefer a stand mixer with a paddle attachment)
1 pot to heat something gently on the stove
The ingredients are as follows (Not measured exactly for reasons explained later):
Locust bean gum
Sugar (if needed)
Step 2: Puree Your Peas, Mix in Your Enzyme, and Leave It for a Spa Day
This will be your longest step, but the VAST majority is just letting something sit in warm water while you go to sleep.
Grab your immersion circulator, fill a container with water, and set the device to about 155 degrees Fahrenheit.
While the bath is heating up, throw your peas in a blender and blend them into a nice, smooth puree. Once pureed, mix in a bit of the amylase enzyme. Because amylase is an enzyme, the more you use, the faster it will work. There is a similar reason for why I've chosen the 155-degree temperature for the water bath. That temperature will speed up the enzymatic reaction of the amylase. At this point, I have little doubt that you're asking yourself "What is amylase and why am I putting enzymes in my food?" Well, have you ever chewed up a cracker and let it sit in your mouth for awhile until it started to taste sweet? Amylase is the enzyme that causes that to happen. Amylase is an enzyme that breaks starch down into sugar. Specifically, it breaks down one amylose molecule into three glucose molecules. Amylase is something that is used in certain forms of alcohol fermentation to assist in providing sugars to feed yeast to create alcohol. Here, we're using it to naturally sweeten the peas without adding any extra sugar.
Once your peas are pureed and mixed with amylase, put the puree into a bag and put that bag into your water bath. Leave it there for about 12 hours to ensure that the amylase has ample time to do its thing.
Step 3: Centrifuge Your Peas
The next step is pretty simple. Simply remove your puree from its water bath, fill up a squeeze bottle with it, and fill your centrifuge tubes. You're going to want to fill your centrifuge tubes on a scale to ensure that each one is filled evenly. Bad things can happen when different amounts of weight are put into centrifuge tubes and placed in a centrifuge together. I've heard of larger centrifuges exploding in labs. The Waverly CL4M that I use will, fortunately, shut itself down if it detects a weight imbalance.
Once your tubes are all filled, centrifuge away. The time it will take will vary based on your centrifuge. I put the tubes in mine for about 15 minutes and it came out with the result you see. Once your puree is centrifuged, you'll see the three layers mentioned above. All you want for this is the liquid. Definitely save the middle "pea butter" layer though. That stuff is incredible. For the most part, the solids will remain in the tube as a puck until you coax them out. Just to be safe, pour the liquid through a coffee filter into your bowl to catch any little particles that might have made their way out of the tube.
Step 4: Test for Sugar Content
In this next step, all we're going to do is check the sugar content using our refractometer and adjust if necessary. The pictures I've added show the sugar content of the peas before amylase was added, and about an hour after. Unfortunately, I forgot to take a picture of the final outcome after the 12-hour water bath, but it ended up at about 24%.
For a sorbet, you want a sugar content between twenty and thirty percent. I'd say 25%-28% is the sweet spot. Why so sweet you ask? 1. It's more delicious that way. 2. The sugar causes something called freezing point depression. It reduces the temperature at which the liquid it is suspended in freezes. This allows the syrupy, sweet mixture to freeze slower than the rest of the water, giving the sorbet it's texture. If we were to use too little sugar, the sorbet would come out as a solid block of ice. Too much and it comes out as a slush.
What do you do if your pea water isn't sweet enough yet? Add more sugar. You can use any type you'd like. I'd recommend going with corn syrup for the added creaminess to your final texture. Don't worry if you don't have to add any sugar, the locust bean gum we are using will also assist in developing a nice texture.
Step 5: Add Your Flavor Enhancers
Now we're going to add a couple of flavor enhancers. First off, a little bit of lemon juice. Fun fact, acid is a flavor enhancer. I do not know why, but things tend to taste better when the pH level is brought down a bit to the point of mild acidity. Some chefs in very highly praised restaurants go as far as to pH test certain things like sauces, wines, etc. to ensure that they are bringing the most optimal flavor to the table. I didn't go quite that far. Just add a little bit of lemon juice until you like how the base tastes. I personally went for something that didn't really taste like lemon, but had a hint of fruitiness to it. You'll notice that the base will taste better after this step regardless of how little you use. Or worse if you overdo it. Try to avoid that.
Next up, the universal flavor enhancer you see in nearly every recipe you've ever seen, salt. Salt, like acidity, just makes things taste better (when used in proper amounts.) This is another one that you're going to just want to add until you like the taste. Don't add so much that it tastes salty. Just use enough to make the flavor of the base pop a bit.
Step 6: Adding the Last Ingredient
This is the step we have two different scales for. First up, you're going to want to weigh out how much sorbet base you have. Just fire up your scale, switch it to grams/metric, put a bowl on it, zero it out, and pour in your base. Why are we doing this? The locust bean gum we're about to add acts as a stabilizer and thickening agent and is used in VERY small amounts. You need to know how much base you have to know how much locust bean gum to add to it without overthickening it.
Once you know the weight of your base, transfer it to your pot on the stove and start to warm it up. Low heat will do here. We only need it to get up to about 120 degrees Fahrenheit. It's okay if you go passed this, but the hotter it gets, the longer it will take to freeze after this step.
While your base is warming, measure out your locust bean gum. Locust bean gum works best at about 0.1-0.3% of the weight of whatever you're adding it to. This is a crazy small percent and this is why we want to know precisely the weight of our base and why we have an oddly precise little scale. I'd go for about 0.2-0.25% by weight of locust bean gum for a nice texture. Once that's weighed out and your base is warmed, remove the pot from the heat, add the stabilizer to your warm base and mix it in. I recommend a whisk. Whisks are good for this sort of thing.
What is this locust bean gum doing you ask? Good question! When one makes an ice cream, sorbet, gelato or what have you, they are really making and freezing a foam. You are aerating these base mixtures to create tiny little bubbles and cooling them so they freeze. This stabilizer we're adding is going to help form small, even bubbles that will create a smoother texture. At the same time, it also acts as a thickener that is going to make the sorbet seem creamier.
I told you I'd explain why I didn't put specific measurements earlier. Here's your explanation. A lot of what goes into making this is either added in a specific ratio or to taste. I can't tell you how much base you're going to end up with or how much salt or lemon you will want to add or a specific amount of locust bean gum to add. I can only tell you what to add and in what ratios you want them.
Step 7: Freezing Your Sorbet
There are a number of different ways you can do this last step. You can go the traditional route of using an ice cream machine if you'd like. If you go that route, refrigerate your base to help cool it down beforehand. I like to go with a quicker route in order to end up with a better texture. One thing that lends the texture to an ice cream or sorbet is the size of the ice crystals that have formed it's structure. The faster you're able to freeze it, the smaller the ice crystals will be and the smoother the texture will be in the final product. A speedy way to freeze something is to use dry ice, which you can get in your local grocery store. Just throw some dry ice in your food processor to powderize it before you use it. Then set up your stand mixer with a paddle attachment, add your base, start it up, and add the powdered dry ice little by little until it's a sort of soft serve consistency.
For me, dry ice isn't fast enough. I like to use liquid nitrogen because I'm a madman and I can. Liquid nitrogen is significantly colder than dry ice and will, therefore, freeze your sorbet much quicker, creating smaller ice crystals and an even smoother texture. The setup here is the same as with the dry ice. This time, instead of adding powdered dry ice little by little, I add a slow, steady stream of liquid nitrogen until I've reached the desired consistency.
Once your base is frozen, you can eat it right there if you'd like. I'd recommend pouring it into a container and letting it freeze further in your freezer though. After allowing it to freeze, it will be a bit more solid and scoopable with a traditional ice scream scoop.
Step 8: Eating Your Sorbet
This last step is a toughy. I'd recommend getting yourself a spoon, or it could get messy. All you need to do is dip your spoon in there, lift it up, and shove it straight in your mouth and enjoy it.
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