Maybe it was reading recently about Heston Blumenthal opening up a mid-price range 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 at home? 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 fingers get everywhere!
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 syrup has in ice-cream, why it helps to maintain it soft.
Oh no…this means finding out about inverted sugar…sucrose, glucose, fructose, disaccharide, monosaccharides, citric acid, hydrolyze, ph neutral, sodium bicarbonate, rogue glucose and fructose molecules…tangly molecules…different depths of inversions…fully inverted…partial inverted…I think I’m getting a flashback to the terrible effects of posting the Bronze Pasta post!
I would make my life easier if I just stuck to recipes discovered that liquid glucose worked and that’s all…leave it that. Unfortunately having this blog it has given me the urge to try and discover why things happen…takes me a long time to get there but…eventually some of it sticks.
I was surprised in my initial search on the net just how little information there is about liquid glucose. My sources of information have come from How Baking Works by Paula Figoni, Heston Blumenthal’sIn Search of Perfectionand of course Harold McGee’s Food & Cooking.
I would like to point out in Harold McGee’s book there is no entry on liquid glucose nor inverted sugar. His information is on corn syrup which according to McGee has properties like concentrated sucrose syrup. After reading up on the properties of corn and sucrose syrup, everything points to this little jar you can buy in the supermarket and pharmacy is inverted sucrose syrup; sugar just like the one you add to your cup of tea, only inverted. Doesn’t say on the bottle.
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 so special is that once it gets to this 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 crystalise. This is what makes inverted sugar special, that is 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 and wheat starch. In the US cornstarch seems the most popular choice.
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.
Why Add Enzymes in Some Sugars and Not Others?
Just to complicate things a little here I discovered that sugar like sucrose which is made from cane already has fructose present in it’s molecule make-up: sucrose is part fructose and part glucose. However, the sugar made from cornstarch, favoured by manufacturers is mainly made up of glucose hence why they add an enzyme to turn some of that glucose into fructose to make it even sweeter…remember that fructose is incredibly sweet in comparison to other types of sugar.
This information of the difference in the make-up between cornstarch and sucrose took me a while to understand because none of the books specify this difference. I spent most of the time confused why enzymes were introduced to make fructose when producing inverted sugar but in another book it states sucrose was part fructose.
It wasn’t until now while writing up this entry and doing a little wikipedia search putting together with the information from the books I’ve been able to understand that sucrose (from sugarcane) is part fructose but cornstarch isn’t. Cornstarch is mainly glucose. So why don’t manufacturers use sucrose if already has fructose in it? I’m guessing it always comes down to the cost of raw materials when manufacturing.
The other interesting thing about inverted sugar is because of the residual acid left in, it’s a hostile environment for microorganisms to grow.
A professional baker makes use of inverted sugar by replacing a small amount of the sugar in the recipe with the syrup and making baked goods softer for longer, add strength and pliability to pulled sugar and spun sugar, thicken coulis and prevent cyrstalisation in desserts and ices, as well as making icings and fondants shiny and smooth.
The photo above is of pear and vanilla syrup I used to poach pears in and then made into inverted syrup…my own version of golden pear syrup…accidentally
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 into inverted syrup. I still have half a jar left, a year later, perfectly stable and flowing, tasting wonderfully of pears and vanilla. Even though I knew how to produce this I didn’t know then how it exactly happened.
Not knowing why it happen I naturally assumed it was just a simple matter of boiling down sugar syrup, my head wasn’t full of inverted sugar then. The trouble with my theory of simply boiling down sugar syrup was…it didn’t work. I tried to re-create this syrup again but instead all I achieved was to crystalise the sugar, which harden when I poured into a measuring jug…and there it stayed sitting on my widow-sill for about 3 months. Photo below of the crystallised sugar in a pan of water, trying to boil down the sugar to clean the jug. Incidently the only way I could get this crystalised sugar to melt enough again was in the oven medium heat.
When I first began to research liquid glucose during this Christmas holidays I realised then there must have been an acid present in the pear syrup for it to work the first time. None of this made much sense at the time since the only ingredients in my poached pears are; sugar, water, vanilla, pears. The recipe hadn’t changed so why did it work first time round but not the second time? Is there acid present in the pears? And perhaps more so in some pears than others? No…none of this was true.
Do you know how it all fell into place? At some point I remembered that most of the time I use lemon juice if I’m peeling pears, especially peeling a large number of pears to stop them discolouring before putting them into the syrup for poaching. However…I don’t always do this, occasionally I put the pears without brushing them with lemon juice straight into the syrup….Bingo! It now made sense.
The pear syrup I was so proud of, tastes so gorgeous, was one where I had brushed the pears with lemon juice first, therefore introducing acid to the syrup and hence it started the process of inverted sugar….yeah! I did feel a bit clever when I solved the puzzle, I must say!
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 Heston’s book, he visits the factory of Tate & Lyle’s Golden Syrup and for those who are not familiar with this syrup it’s very famous in the UK and used in all sorts of baking and for pouring on to your porridge. The employee at the factory Ian Clark tells Heston how the process of achieving the famous golden syrup is done. They start with sucrose, which is made up of two simpler sugars: glocuse and fructose, he goes on to explain, “…if you heat sucrose in the presence of acid, the sucrose splits into its constituent parts…this messes up the orderly crystalline structure, resulting in a thick liquid. And the disorder prevents the sucrose from re-forming – rogue molecules of glucose of fructose keep getting in the way”.
He goes on to explain in the book how they refine the syrup further to make the special flavour and colour of golden syrup.
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).”
In the How Baking Works book, it goes into detail on the production of corn syrup and detailing again the breaking up of molecules into smaller units.
I learned from these books that once you break down the properties in the sugar with the presence of acid they find it impossible to revert back. When you use this inverted sugar in a recipe the molecules help to stop the other sugars in that recipe from crystallising or in the case of ice-cream stop ice-crystals absorbing more water and becoming larger, causing the ice-cream to be rougher.
How To Measure Liquid Glucose and How Much To Use in a Recipe
Somewhere but can’t remember where (if you find where let me know!) 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. If you are measuring out cold liquid glucose you can be weighing out 20 grsms of it using a tablespoons but if it’s warm it’s around 15 grms, so over say 4 tablespoons you could be talking a 20 grms difference which is considerable when working in small quantities and then 4-6% of a recipe.
The Pear Syrup – December 2009
This was my happy accident of inverting my own pear syrup, taste 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.
The very famous Tate & Lyle’s Golden Syrup tin…when I first took the photo of this tin it was because I wanted to show how golden syrup is also an inverted sugar, it says on the bottom, “Partially Inverted Refiners Syrup”…at the time I had no idea what that exactly meant…now I do…and I’m a happier person for that…hooray!…and if I’ve missed something let me know!
I noticed 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, I think it was third time lucky. Now you see recipes for caramel cages with liquid glucose as well as mousse, ice-creams, tortes and other desserts. I suspect if I try making the caramel cages again with liquid glucose I won’t be cursing them so much!
{ 7 comments… read them below or add one }
Good job on some heavy research! There’s another reason why melting granulated sugar in a saucepan might produce crystallization; if some of the sugar syrup on the side of the pan begins to crystallize while it is being cooked, that crystallized sugar syrup tends to affect the entire batch – candy makers (who may not want acid in the mix) solve this by using a wet brush during cooking and making sure no crystals are allowed to form.
I too created an inverted sugar syrup last Christmas season when I made my own candied citrus rind – you have to cook the rind in a sugar syrup until it becomes translucent, then drain and roll in granulated sugar. Of course, you’re left with a large amount of citrus flavored syrup – no way I could throw that away! I too had no idea that it was ‘inverted sugar’ (until you told me here!). I bet the reason why the citrus syrup has no crystallization issues is because of the high acid in citrus.
Thanks for a good, informative post again, Azelia – really nice job.
thank you dr fugawe – yes you’re right it’s a good tip! I learnt that from the Roux Brothers, they are famous classic French chefs here which have now passed on their restaurants to their sons…I learned most of my pastry making when I was young from their books.
…and yes I believe you’re right about the citrus peel, make sense, doesn’t it? Talking of citrus I’m going to try and make salted preserve clementines see how they turn out.
Azelia, I normally read your posts because they get my appetite going! Tonight, though, after dinner, I remembered your sugar mystery and whoa, surprise, it was the lemon whodunnit! Good information.
I think maybe I will look at the lamb, quince and cardamom casserole for this weekend…
try the lamb with the quinces, you’ll like it.
I have only recently discovered liquid glucose. Addind a little bit of it to burfies (Indian milk based, toffee like sweets) stops them from getting hard. I already have plans to use it in my next batch of Kulfi icecream.
Let us know how the kulfi turns out Mamta.
Thanks for this info, really helpful in understanding what’s going on under the covers. I was recently given a (Top Secret
recipe for ‘Unforgettable’ chocolate brownies which called for 30g of liquid glucose (which I discovered was quite hard to find… eventually found some at a baking supplies store).
Your advice on measuring out when warm is a great idea. I think my 1st attempt at these brownies didn’t go well because I put the (room temp) liquid glucose into the mix almost last, and it was practically as thick as the brownie mix at the time and probably didn’t distribute very well. The outer edges of the brownies came out nice and chewy, but the centre was soft and gooey, even after baking a lot longer than expected it just wouldn’t firm up. Now I think I know why.
The 2nd perspective on the same advice is to use it in careful amounts – the 2nd time I made these brownies I just put a ‘dollop’ into the mix (albeit earlier in the mixing in an attempt to get it more evenly distributed)… but my brownies stayed seriously gooey once again, this time I think because I simply used too much liquid glucose.
But the best lesson from your post (IMHO) is WHY this liquid glucose is in the recipe in the 1st place. Now I know
I can almost taste my third attempt and I think they’re going to come out ‘Unforgettable’ thiis time, for sure!
Thanks :
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