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When visiting friends who regularly brew their own beer, they told us about this great sugar syrup they had made to add to their beer. It was a dark brown, almost coffee/chocolatey, syrup with a great flavor. They had made the syrup by simply boiling sugar (sucrose) in water with some diammonium phosphate.
We had boiled sugar syrups plenty of times before but never had we tasted this type of flavor in our syrup. It got us curious. They had clearly initiated fascinating chemical reactions that don’t normally occur when cooking sugar syrups. The color and flavor were vastly different than those of ‘regular’ sugar syrups you make by just boiling some sugar in water (e.g. to make candy)! Could the diammonium phosphate (also known as yeast nutrient) have something to do with it? And how does that work?
Of course, it sparked our interest and we started doing a range of experiments, opening up Pandora’s box on sugar chemistry! Along the way, we found a few great ways to tweak your sugar syrups to create unique and surprising products.
The Chemistry of Sugar Syrups
Most sugar syrups are simple, transparent solutions of sugar in water. They taste sweet for sure, but otherwise don’t have too much flavor. You might use them to make a drink or drizzle them over a cake.
Alternatively, you might be cooking your sugar syrups to make candy. By boiling a sugar solution until the desired boiling point is achieved, you can tweak how your candy behaves. Will it flow, crack or bend? That is all determined by how you cook your sugar syrup (we do a deep dive into cooked sugar syrup stages here).
However, as we noticed when tasting that syrup our friends made, there’s more to cooking syrups than just influencing their flow properties (rheology). There’s a lot of chemistry that you can control to create sugar syrups with new flavor and color profiles!
Sugar syrups might make you think of maple, agave, brown rice, or corn syrup. Whereas these are all syrups made up of a mix of sugars, for this article specifically, we’ll be focusing on sugar syrups made from common sugar: sucrose.
Most sucrose is made from sugar beets or sugar cane both of which naturally contain a lot of sucrose. Sucrose is a carbohydrate, more specifically, a disaccharide. It is made up of two monosaccharide molecules (glucose and fructose) that have reacted together to form one molecule. Sucrose is sweet, dissolves well in water, and if you look closely, you will see that it is made up of a lot of small individual crystals.
Crystallization of sugar syrups
Sucrose dissolves well in water, and dissolves even better in warm water. Unfortunately though, when you cool down the water again, the solubility of sucrose goes down again as well. As a result, you might have made a nice thick fluid sugar syrup, that is full of sugar crystals after a few days. Not a desirable situation if you’re making a sugar syrup that you’re planning to keep for a little longer.
When making rock sugar you actually do want the sugar to crystallize! When making rock sugar you purposefully dissolve too much sugar in hot water and leave it to cool, resulting in the growth of beautiful crystals!
As such, when you’re making a sugar syrup you have to make sure you make (or use) the syrup in such a way that the sugar doesn’t have a chance to crystallize. One way to do so is to use the syrup quickly (as you’d do when drizzling it over a cake). Another way is to break down some of the sucrose into its two building blocks: glucose and fructose. Glucose and fructose don’t crystallize as easily and so prevent crystallization and increase the stability of your syrup.
By breaking down sucrose into glucose and fructose, you make “invert sugar”. This happens through a chemical reaction called hydrolysis. Invert sugar is slightly sweeter than sucrose and dissolves even better in water, making the resulting syrup less viscous.
Often you’ll want some inversion of sugar to happen when making invert sugar, but not too much. Inversion of sugar will take place ‘automatically’ if you leave sucrose in hot water for long enough. Just how fast it happens depends on factors such as concentration and temperature. For instance, the warmer the water, the faster the sugar hydrolyzes.
Impact of batch size
Keeping a sugar solution at a high temperature for an extended time period will increase the degree of inversion of the sugar. This is important to keep in mind when choosing batch sizes to make your syrup. Larger batches generally require longer cooking times simply because it takes longer for the syrups to heat up. As such, a 5 liter batch might ‘invert’ a lot more than an identical 0,5 liter batch!
In some cases, you might not want any inversion to occur, however, for the stability of most syrups you actually do want some inversion to happen! The inversion will help prevent the sugar from recrystallizing. If this is important to you and you are greatly reducing the batch size of your recipe, make sure you cook your sugar syrup more slowly to invert enough sugar to prevent crystallization.
Using acids or enzymes
Alternatively, you can speed up the reaction by adding acids to your sugar syrup while it’s cooking (e.g. lemon juice, citric acid, or vinegar). Manufacturers might also make invert sugar by adding the enzyme invertase which cuts up the sugar. By using this process manufacturers don’t need to use as high temperatures.
Browning reactions: Caramelization & Maillard reaction
Whenever you’re heating sugars it’s important to keep in mind one last important phenomenon: browning reactions. Sugars are quite reactive and can participate in a lot of chemical reactions. The two most important ones are caramelization & the Maillard reaction.
Both are complex sets of chemical reactions that can take place once the temperature is high enough. For caramelization to happen you’ll only need sugar to be present. Once it’s hot enough (starting at about 160C) it will start to turn brown and change flavor. The most important colorants formed during these reactions are large molecules called caramelan, caramelin, and caramelen.
The Maillard reaction is slightly different. It can take place at lower temperatures (it can even happen at room temperature, though will be so slow that it might take months before you notice it happening) and needs something else besides sugars: amino acids. Amino acids are the building blocks of proteins and contain a nitrogen molecule. These nitrogen containing components react with reducing sugars (e.g. glucose, sucrose itself can’t actually participate) to form brown colors and a lot of flavors!
Making Flavorful Sugar Syrups
With this knowledge in your pocket, you can make and tweak your own sugar syrups. All start the same way: by dissolving sugar in water and heating this sugar solution. Just how you treat the solution will impact how your syrup turns out.
To give you some inspiration to get started, we tested making 4 different sugar syrups. We cooked all to the same initial temperature (146°C / 295°F) to ensure we’d heat the syrup hot enough for some chemical reactions to take place. We did this twice to every syrup, cooling it down in between by adding a set amount of water. Finally, we cooled them all down by adding back some more water and cooking them until a temperature of 113°C (235°F). This would ensure the final syrup was liquid as we discussed in an earlier article on sugar syrup cooking stages.
Each syrup differed in the ingredients we added:
- Reference: sugar + water
- Adding nitrogen: + diammonium phosphate
- Adding acid: + lime juice
- Adding alkaline: + baking soda
Each condition made for a very different syrup, differing in both flavor as well as color and viscosity!
Reference: sugar + water
Bringing sugar + water to 146°C (295°F) twice and then cooking it to 113°C (235°F) gave a very light yellow, free flowing sugar syrup. This was to be expected. Under normal conditions sugar doesn’t caramelize or react extensively under these conditions.
Impact of diammonium phosphate
As you can see in the images added to the article, the sugar syrup made with diammonium phosphate clearly was darkest of all four syrups. It also had the strongest flavor, not (yet) bitter, but definitely less sweet than the reference sample. So why and how does diammonium phosphate impact the color and flavor of a sugar syrup that much?
To understand this, we had to dig into the literature on ‘caramel colors’. These colors are used by manufacturers to color their products (e.g. soft drinks, or baked goods) a desirable brown color, without actually having to brown the product by heating it for instance.
The caramel colors can be bought as such, as caramel colors. They are also made from sugars that are heated under controlled conditions. Also, either sulfite or ammonium compounds can be added during the process. These help accelerate certain reactions to occur to ensure the desired color and flavor are formed. Caramel colors are named based on how they’re made and which of these compounds have been added during the process. That splits them in four different groups:
Since these are food additives, they’re quit well described in both literature as well as legislation and tend to be split into four different groups:
- Type I: plain or caustic caramel; no sulfites or ammonium compounds were used
- Type II: caustic sulfite caramel; sulfite compounds are used, no ammonium compounds
- Type III: ammonia caramel: ammonium compounds are used, no sulfite compounds
- Type IV: sulfite ammonia caramel: sulfite and ammonia compounds are used
In Europe these colors are labeled as E150a-d. These additives are meant to be used for coloring specifically, not necessarily for flavor purposes. These colors are very stable, even under high temperatures, and is why they can be found in a lot of different foods. Not all caramel colors are stable in all foods. The reason our beer brewing friends used a sugar syrup made with an ammonium compound (diammonium phosphate) is likely because the type III caramel color that its made that way is very stable in alcohol and thus beer!
Legislation prescribes just which ammonium and sulfite compounds may be used. The ammonium compounds that may be used are: ammonium hydroxide, ammonium carbonate and ammonium hydrogen carbonate, ammonium phosphate, ammonium sulfate, ammonium sulfite and ammonium hydrogen sulfite. For sulfites the following may be used: sulfurous acid, potassium, sodium and ammonium sulfites and hydrogen sulfites.
So what happens when you add ammonia to caramels? We’ll look at our specific ammonium salt first: diammonium phosphate. As you can see below, diammonium phosphate contains nitrogen. This enables the Maillard reaction to take place, which can take place at temperatures well below those of sugar caramelization reactions. Also, the Maillard reaction can lead to the formation of melanoidin. This molecule has a very dark color and helps to achieve that dark dark syrup color.
The exact chemical reactions that occur in these complex system are still not completely understood. There are simply too many molecules that are formed during these reactions. Researchers have compared different ammonium salts with one another and concluded that diammonium phosphate (also called DAP) was one of the most efficient for forming these dark colors. Why though is not known exactly.
A Note on Ingredients Used by Manufacturers
Most commercial sugar syrups or caramel colors don’t declare these added ingredients since they are used as ‘processing aids’, meaning they’re used during the process. Unfortunately, that makes it hard to figure out how syrups were made to help understand their chemistry.
Impact of lime juice
When adding lime juice to our sugar syrup, two things changed compared to the reference sample:
- The resulting syrup was a lot more liquid and less viscous
- The final syrup was noticeably darker
The syrup also tasted a bit more acidic than the reference sample. However, since we added the acidic lime juice, this was to be expected and is not something we’ll dive into here.
The sugar inverts
Based on what we discussed earlier, that difference in consistency can be explained by the inversion of sucrose. The acidity of the lime juice (which has a pH-value <3) combined with the heat while cooking the syrup greatly accelerates the inversion of sucrose, breaking it down into fructose and glucose. This is what makes the syrup less viscous. Also, it will make it a lot more stable against crystallization!
Caramelization speeds up
Caramelization reactions are complex sets of reactions of which the speed depends a lot on the conditions. It is well known that they speed up at both low (<3) and high pH-values (>9). These conditions are very favorable for a few rate-limiting steps in the reaction mechanism, pulling along the entire reaction process.
Also, glucose and fructose have slightly different caramelization temperatures than sucrose does. It is well known that fructose can start to caramelize at tempertures below that of sucrose. Since the increased rate of inversion will create a lot of fructose and glucose, this helps drive caramelization.
As such, it makes sense that the lime juice sugar syrup is darker in color. The caramelization reactions could simply take place faster.
Impact of baking soda
Last but not least, the impact of baking soda. Baking soda is the opposite of lime juice, it’s a base (so has a high pH-value) instead of an acid. High pH-values can also speed up caramelization, much so like low pH-values can.
As such, it makes sense that the baking soda sugar syrup is a lot darker in color than the regular sugar syrup! Unfortunately, the sugar syrup that we made with baking soda was also very much impalatable. It tasted quite disgusting, with a clear metallic aftertaste. If you’ve ever added too much baking soda to a baking recipe, you will know what we’re talking about. It makes the sugar syrup useless in situations where flavor is of importance.
Try it yourself
Now that you know the chemistry of these different sugar syrups. It’s time to see how you can tweak and change your simple regular sugar into an interesting concoction. The instructions below provide a starting point, but we’re sure there’s more to explore. Leave a comment if you’ve tested and found something interesting!
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Wikipedia, Diammonium phosphate, link, visited May-3rd, 2021
Wikipedia, Golden Syrup, link, visited May-3rd, 2021