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Making Ice Cream: The Science of Ice Cream

on Friday, 03 September 2010. Posted in Tips, Reviews, Tips & Info, Reviews and Tips

Let there be ice cream!

Whenever I do something, I go balls to the walls with it and that rings true for making ice cream.  My thinking is that if I understand it's science, how it's made and what role each ingredient plays I should more easily be able to make my own.  Knowledge allows me to experiment a bit without blowing up the kitchen too badly.  I guess my thirst for knowledge is also partly due to the fact that I'm a huge nerd.  And, not the type with the bandaid on my glasses so much as the type that makes every effort possible to be a walking encyclopedia.

So, exactly what is the science behind ice cream?

Technically ice cream is a colloidal emulsion in which there are two or more ingredients that don't want to cooperate on a molecular level.  In other words the three most essential ingredients in ice cream fight like cat and dog.  As ice cream-ists we have to stir, churn and freeze the ingredients into submission.

Why can't we all just get along?!

The three culprits are fat, water and air.  The fat and water in ice cream just don't want to play nice and the air bubbles that provide the lightness and scoop-ability (yes, I invent words)...  Well, they just want to behave like a gas and float away.  So how do we force these ingredients to hold hands and sing songs together instead of being hell bent on getting as far away from each other as possible?

Well, there are two important elements that keep all of this chaos in check - ice and emulsifiers.  Ice cream is actually a mixture of fat and air suspended in a matrix of tiny ice crystals.  The fats in ice cream don't actually mix with water and freeze.  Only the water freezes creating an icy cage to trap the tasty fats.  Emulsifiers are substances that act like a glue of sorts to stabilize the whole she-bang.

Emulsifiers in Ice Cream

If you read the ingredients contained in most commercial ice creams you'll see xanthan gum.  Xanthan gum is one of the most common emulsifiers in ice cream.  It's typically derived by processing glucose.  If you look at a bottle of store bought salad dressing you'll notice that the oil and vinegar are stable and the spices are suspended...  In short, that's what xanthan gum does.

Back in the good ol' days egg yolks were used as an emulsifier.  Xanthan gum became the replacement for egg yolks because of it's availability in powdered form, it's low cost and it's effectiveness in very small quantities.  It can even be used in quantities as small as 0.5%.  But, all that science and penny pinching has a price - xanthan gum just doesn't contribute the flavor that egg yolks do.

Modern science always strives to do things faster, better and cheaper.  More often than not something ends up being left out and years later someone who has been struck by a bolt of nostalgia pulls off the blinders.

"Hey!  The old way of making butter tastes better!  And, It's not even close to the molecular composition of plastic! Hmmm...  Tell me again why we used the fake stuff?"

Well, ice cream is no different.  Many of the old brands have been "re-branded" as premium ice creams.  And, rightfully so.

I think egg yolks add a flavor that is far superior to the flavor of store bought ice cream but the inclusion of egg yolks can also be a determining factor as to whether or not it can be called ice cream at all.  In fact, the FDA states that if a frozen product contains 1.4% or more egg yolk solids then it is officially not ice cream.  It's frozen custard.

Well, I'm not really sure how the FDA would classify my recipes but that's okay.  I have my own classification:  Kick Ass.  So you can come on over to my house tonight.  We're having Kick Ass for dessert.

The Role of Ice Crystals in Ice Cream

The way in which the ice crystals are formed is also a crucial factor in making good ice cream.  If the ice crystals are too large the ice cream will seem gritty.  When the ice crystals are small they melt in your mouth before you have a chance to notice that they're there which releases the creamy fats that make ice cream taste so good.

So how do you make the ice crystals so small?  Well, you need the perfect temperature and the perfect speed of course!  In an effort to get ice cream into their bellies in a timely manner people often crank too fast when using one of the hand crank ice cream maker doodads which makes gritty ice cream.  If the ice cream freezes too fast then you'll end up with a sandy texture.

So, if you're using a hand crank ice cream maker then it takes practice to get the right speed and temperature.  If I didn't appreciate the mystical charm behind doing things the old fashioned way I wouldn't have written this article but there really are some things that have been improved upon since the good ol' days.

Electric Ice cream makers are certainly one of those things.  They provide a consistently perfect speed and the perfect temperature to form itsy bitsy teeny weeny yellow polka dot bikinis.  Er...ice crystals.  The only trial and error involved with a decent electric machine is your recipe and how long to leave it in the ice cream machine

It's funny how I'll take extra steps to use fresh vanilla or use egg yolks in an ice cream recipe but I'm too lazy to turn a crank.  I don't feel bad though.  I could either be turning a crank or writing another article!  I'm out.

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Comments (4)

  • 29 September 2010 at 16:37 |

    Great article :)

  • Matt Kay
    30 September 2010 at 15:21 |

    Thanks Spice! I appreciate the feedback.

  • Boomer
    01 October 2010 at 12:23 |

    Your article has inspired me to make some ice cream. We have a machine, but have only used it once. I'm looking at your chocolate ice cream w/ cayenne. Just picked some fresh cayenne peppers from the garden and I would like to use them rather than the dry. What do you think?

    • Matt Kay
      02 October 2010 at 13:54 |

      I don't think it would work as well. The cayenne in the my recipe is ground so it's like having little tiny flecks of spice hit the back of your throat when you swallow. It's like the culinary equivalent to a fourth of july sparkler. I'm not sure how you'd use fresh ones to the same effect. You couldn't puree the peppers because it would change the texture and the flavor. You could slice them and add them but it might be a little funky to bite into a chunk of pepper.

      I would definitely stick with dried, ground peppers for recipes like this. You could use ancho chile powder as a substitute and it would add a richer flavor and I've heard of people using chipotle too although I've not used it in any of my recipes.

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