making sugar syrups with different additives

Controlling Color & Flavor of Sugar Syrups – Steering Browning Reactions

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 syrup cooked to 105C
A very simple syrup made by boiling sugar (sucrose) in water to 105C. It’s colorless, sweet and flows easily.

Sucrose chemistry

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.

sucrose molecule
A sucrose molecule: made of glucose & fructose

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!

rock sugar left over
Crystallization in a sugar syrup, great if you’re making rock sugar, not so great if you just want to make a flowing sugar syrup.
Preventing crystallization

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.

sugar crystallized at bottom of maple syrup vessel
Even maple syrup can crystallize over time! When there is simply too much sugar for the available water you will see crystals ‘growing’ at the bottom.

Invert sugar

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.

sugar cooked to several caramel stages
Sugar caramelizes at 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.

Maillard reaction

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:

  1. Reference: sugar + water
  2. Adding nitrogen: + diammonium phosphate
  3. Adding acid: + lime juice
  4. Adding alkaline: + baking soda

Each condition made for a very different syrup, differing in both flavor as well as color and viscosity!

Four sugar syrups, each made according to the same protocol (bring to the boil to 146°C, add some water, bring to 146°C again, add more water and heat to 113°C). The only difference: the 3rd ingredient. It clearly shows how these added ingredients impacted the chemistry of these syrups!

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?

Caramel Colors

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.

rock sugar kandijsuiker
Kandijsuiker, this is a sugar that naturally has a brown color, without any extensive cooking.
Ammonia caramels

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.

diammonium phosphate
Diammonium phosphate

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:

  1. The resulting syrup was a lot more liquid and less viscous
  2. 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!

making sugar syrups with different additives

Making Sugar Syrups

Prep Time: 5 minutes
Active Time: 1 hour
Total Time: 1 hour 5 minutes

This experiment shows you how a sucrose (sugar) solution can behave under different conditions when heated. It shows the complexity of the chemistry involved. You'll start by making a control in which you simply heat a sugar syrup to a set temperature in several stages. Next, you'll be adding other ingredients to this sugar solution to test their impact on the heating process.

You will be testing an acid (e.g. lemon juice) and a base (e.g. baking soda) to test the effect of pH on the reaction. You will also be adding a salt that contains nitrogen and phosphate to test the effect of the presence of those.

Materials

  • 400g of sugar (or more if you want to test more conditions!, you need 100g per condition)
  • Water

Testing agents

  • Lime or lemon juice (from a bottle, or freshly squeezed) or citric acid (in powder form)
  • Baking soda
  • Diammonium phosphate (may also be called yeast nutrient)

Tools

  • A sturdy pan with reasonably high sides so you don't run the risk of splashing (e.g. a saucepan)
  • Scale
  • Stovetop
  • Small cup to measure water
  • Thermometer
  • Heat proof glass jars

Instructions

Control

  1. Weigh 100g of sugar with 26g of water in your saucepan
  2. Bring the mixture to a boil on a low/medium heat. Once it's boiling give it a very gentle swirl if not all the sugar has dissolved yet. If all the sugar has already dissolved, don't touch it. After this, try not to stir or swirl or you might run a risk of sugar crystallizing in the pot.
  3. Weigh another 26g of water in a separate cup
  4. When the sugar solution has reached 143°C immediately pour in the measured quantity of water. Be careful, the liquid might splash and it's very hot!
  5. Continue to boil.
  6. Weigh another 39g of water in a separate cup.
  7. When the sugar solution has again reached 143°C immediately pour in the measured quantity of water. Again, be careful, it might splash.
  8. Continue to boil the liquid until 113°C. Immediately take it off the heat and pour in heat-proof glass jars to cool down.

Tests

After making your control it's time to make your tests. You do everything exactly the same as for the control, however, in step 1, add your 'testing agent'. Use the following quantities as a starting point, but feel free to vary and experiment with different quantities.

  1. Diammonium phosphate: add 1/4 tsp
  2. Lemon/lime juice or citric acid: Add 3 tsp of juice or 1/4 tsp of powder
  3. Baking soda: add 1/4 tsp

Results

As we described more extensively in the article above, these different additives have a huge impact on the chemical reactions that occur when heating the sucrose solution. Our results were as follows:

cooking various sugar syrups

From left to right:

  1. It is clear that the addition of diammonium phosphate resulted in the darkest color of all. It also had the most viscous consistency.
  2. Boiling a sugar syrup to the above-mentioned temperatures doesn't do too much to the syrup in terms of flavor and color. It was still very light in color and tasted mostly sweet.
  3. The lime juice did improve the degree of browning and had an interesting taste profile. It wasn't as sweet anymore but it was very thin, the sugar had clearly inverted!
  4. Lastly, the baking soda had a nice brown color. However, the presence of metals in our baking soda gave it an awful, metallic, almost bitter, flavor.

Notes

Other interesting experiments you could try:

  • Vary the temperature of the first cooking stages (the 143°C). We would not recommend going any higher with the ammonium phosphate (it will turn very dark), but you could go down lower, though we wouldn't go below 120°C to ensure something still happens
  • Vary the amount of testing agent. If you didn't find the color and flavor strong enough, or you found them too strong, increase or decrease the amount of testing agent to investigate how that impacts colors. Generally, more 'testing agent' will result in stronger flavors and colors.

References

Kwasi Agyei-Aye, May X Chian, John H Lauterbach, Serban C Moldoveanu, The role of the anion in the reaction of reducing sugars with ammonium salts, Carbohydrate Research, Volume 337, Issues 21–23, 2002, Pages 2273-2277, ISSN 0008-6215, https://doi.org/10.1016/S0008-6215(02)00221-5., link

Eur-Lex, Regulation (EC) No 1333/2008 of the European Parliament and of the Council of 16 December 2008 on food additives, link

FAO, Caramel Colours, Prepared at the 55th JECFA (2000) and published in FNP 52 Add 8 (2000), superseding specifications prepared at the 31st JECFA (1987), published in FNP 38 (1988) and in FNP 52 (1992). link

Y. H. Hui, Wai-Kit Nip, Leo M. L. Nollet, Gopinadhan Paliyath, Benjamin K. Simpson, Food Biochemistry & Food Processing, John Wiley & Sons, 2008, p. 83-85, link

Leo M. L. Nollet, Fidel Toldrá, Gopinadhan Paliyath, Soottawat Benjakul, Food Biochemistry and Food Processing, John WIley & Sons, 2012, p.68, link

NPCS Board, Confectionery Products Handbook (Chocolate, Toffees, Chewing Gum & Sugar Free Confectionery), Asia Pacific Business Press, 2013, p. 81-83, link

Alyssa Persinger, Getting to Know Your Syrups: Molasses, Sorghum, Cane Syrup and Golden Syrup, Formaggio Kitchen, June 23, 2014, link

Sengar G, Sharma HK. Food caramels: a review. J Food Sci Technol. 2014;51(9):1686-1696. doi:10.1007/s13197-012-0633-z, link

Thomas A. Vollmuth, Caramel color safety – An update, Food and Chemical Toxicology, Volume 111,
2018, Pages 578-596, ISSN 0278-6915, https://doi.org/10.1016/j.fct.2017.12.004., link

Wikipedia, Diammonium phosphate, link, visited May-3rd, 2021

Wikipedia, Golden Syrup, link, visited May-3rd, 2021

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