Liquid Glucose – The Answer to Perfect Ice-Cream and More

I think it was reading about Heston Blumenthal opening up a restaurant in London where his famous liquid nitrogen ice-cream will be served that jolted this quest of mine; how to make ice-cream at home that stays soft.  After reading Kavey‘s post about an ice-cream shop in Camden Town, London, serving liquid nitrogen ice-cream, it seems there’s a desire for supersoft textured ice-cream.  

Yes, liquid nitrogen makes super-duper soft ice-cream but what’s the answer for the home cook?  What about the rest of us?  Go and purchase yourself a little bottle of liquid glucose, it’s adult and child-safe…urm…unless small child gets their little fingers into the sticky icky jar and runs fingers on your furniture!

This post on liquid glucose is a follow up from Ice-Cream or Sorbet Too Firm in the Freezer? post where I searched into the problem of home ice-cream freezing too solid in the freezer and discovering the answer was liquid glucose, but I wanted to know more about the effect this inverted sugar has in ice-cream, why it helps to maintain it soft.

What Is Inverted Sugar?

It’s sugar that has been boiled down with some water and a little acid until it’s thick and syrup like, it can take as little as 15 mins, at that point it becomes inverted sugar.  

What makes inverted sugar special is that once it gets to the broken-molecule down stage it can’t go back to its former self, its molecules have been broken down to the extent they can’t re-form and crystallise, it stays runny, thick and in syrup state.  

Think of any syrup like golden syrup by Tate & Lyle, molasses or corn syrup and that’s what they are. It can be made from cane as golden syrup is, or potato, rice or wheat starch.  In the US cornstarch seems the most popular choice.

The other interesting thing about inverted sugar is that having residual acid left in, it means it’s a hostile environment for microorganisms to grow.

How and Where is Inverted Sugar Used?

Food and drinks manufacturers are the ones who make the biggest use out of inverted sugar because it makes baked goods stay moist for longer, making shiny smooth icings and fondants, and prevents confectionery and frozen desserts from crystallising.  

With some inverted sugar (ones made from cornstarch) there is an additional enzyme added to the process and what this does is to turn some of its glucose into fructose.  Why?  Because fructose is highly sweet, more so than your table sugar.  And why is this relevant to manufacturing?  Because they can make products sweeter cheaper.

How To Control the Inversion

Manufacturers control how much they want to invert the sugar.   To what point the inversion goes is dependent on its use, the sugar can be fully inverted or have a low-conversion and anything in-between.  They boil down the sugar with the acid until the point they want, then to stop the process at that particular stage they add sodium bicarbonate which brings the ph back to neutral, it means it brings down the acidity in the syrup and holts any further inversion.

Properties of Glucose

From reading up on McGee’s entry he explains, “…long tangly molecules that exist…interfers with molecular motion…preventing other sugars in the candy from crystallising and producing a grainy texture.  All molecules in the syrup are flowing very slowly, and the sucrose crystal faces keep getting covered with chains that can’t become part of the crystal.  (The same behaviour helps minimize the size of ice crystals in ice cream and fruit ices, thus encouraging a smooth, creamy consistency).”

How To Measure Liquid Glucose and How Much To Use in a Recipe

I read you should use between 4-6% of liquid glucose of the total recipe, in the How Baking Works book it states not to use more than 5%.

The easiest way I’ve found to measure liquid glucose is to put the jar in the microwave for 10 seconds or in a pan of hot water.  Measuring out cold glucose by spoon will weigh more than if the syrup is warmed first.  Personally I think it should be done by weight rather than spoons.

I Made Inverted Sugar in the Winter of 2009…accidently

Without meaning to, I turned a simple sugar syrup I had used to poach pears for a recipe into inverted syrup.  I still have half a jar left, a year later, perfectly stable and flowing, tasting wonderfully of pears and vanilla.

The pear syrup tastes so gorgeous, was made because I had brushed the pears with lemon juice first, therefore introducing acid to the syrup and hence it started the process of inverted sugar….unknowingly I had made inverted pear syrup.

The Pear Syrup – December 2009

This was my happy accident of inverting my own pear syrup, tasting wonderfully of pear, great  to brush on pears when making pear desserts or tarts, but it’s used like any regular syrup over pancakes, porridge…

The Pear Syrup – January 2011

A year later and the syrup has not changed…Now that I fully understand how I produced it,  it means I have full control of doing it again.

Below is photo of another pear syrup I tried to boil down but it didn’t contain acid and subsequently did not ‘invert’.   This meant when it cooled again it crystallised and harden to the point it became difficult to remove it from the jug…putting in a pan of boiling water didn’t work, in the end it was only heating up the jug at high temperature in the oven that I managed to rescue the jug.

I noticed many years ago when I tried and eventually succeeded to make caramel cages using a Raymond Blanc’s recipe from his Le Manoir aux Quat’Saisons book, he does not use liquid glucose…and I can tell you these caramel cages were a difficult thing to achieve.  Now you see recipes for caramel cages with liquid glucose.  I suspect if I try making the caramel cages again with liquid glucose I wouldn’t be cursing them so much!

To learn how to make the ultimate smooth texture ice-cream using inverted sugar and jelly read my post: How to make super smooth ice-creams or sorbets.