Pretzels and pH – hacking the Maillard reaction

Why do you dip pretzels in high pH, corrosive lye before baking them? How is this related to brown onions and black garlic? What is the Maillard reaction and can we really hack it?

When making pretzels, a simple dough is shaped into the traditional pretzel knot and dipped in lye (NaOH, sodium hydroxide) before sprinkling it with salt and baking. This lye dunking is what really makes a pretzel a pretzel and gives it that special flavor so many of us love. But how does dipping dough in a corrosive, alkaline solution affect the flavor of what is essentially a bread knot?

Today, a group of vegan bloggers is having a virtual potluck over on Instagram, #plantbasedvirtualpotluck, hosted by @Plantbased.Passport. The theme is Oktoberfest and the dish I decided to bring was pretzels. But rather than making a batch or two of these delicious treats, I decided to dive into the chemistry behind the lye dipping.

In this post, I will outline the Maillard reaction that is responsible for the brown colour and complex flavours developed when cooking food at high temperature, I will look into how these are affected by lye and I will share a little experiment with you.

Maillard reaction

The Maillard reaction [my-yar], named after its discoverer a Louis-Camille Maillard, is a chemical reaction between an amino acid (the building blocks of proteins, see the pH and tofu post) and a sugar, such as glucose or fructose ​[1]–[3]​. Often also refered to as non-enzymatic browning reactions, the reaction creates a molecule where the amino acid and the sugar are bound together. Exactly what the result is depends on which sugar and which amino acid was used. These sugar-amino acid molecules (glycosylamines) then go on to react with other molecules creating all sorts of new compounds. These many different compounds are what give foods cooked at high temperatures their complex flavours and brown colour.

Note that this is not caramelization. While both give brown colours and complex flavours, caramelization is the breakdown of sugars and usually occurs at even higher temperatures.

Quick primer/refresher on chemical reactions

Let’s quickly brush up on chemical reactions. Chemical reactions are when one or more molecules (reactants) turn into one or more molecules (products). One concept is of extra importance in this post: all reactions happen at a certain rate. Several factors affect the rate and it depends on temperature, how many molecules are present, pH and other things.

The Maillard reaction and temperature

Alright, now that we had that quick chemistry recap, is there anything tasty, I mean useful, we can do with that knowledge? First up, we can look at why so many people associate the Maillard reaction with cooking at high temperatures. The answer is straightforward: the reaction rate is simply higher at high temperature. It goes faster. In particular, the Maillard reaction increases greatly above 150 °C which explains why you bake bread, fry onion, deep fry potatoes and barbecue burgers at these higher temperatures.

But there is another important part to be aware of: the rate is not zero at lower temperatures. This means that we can get Maillard reactions at lower temperatures, they are just slower. For instance, when you boil a can of condensed coconut milk for two hours (100°C), it turns into a  brown, rich fudge not unlike Dulce de leche. If you reduce the temperature further, you have to wait even longer to get the same reactions. Black garlic gets its black colour and complex flavor from Maillard reactions occurring over several weeks at 60-90°C (for intance in your rice cooker at home ​[4]​). Miso and soy sauce likewise get their dark colours and complex flavours from these reactions but are processed at room temperature for about a year.

Pretzels, pH and the Maillard reaction

Now you know a bit more about the Maillard reaction and how it creates complex flavours. For the Maillard reaction between the amino acid and the sugar to occur, the amino acid has to lose one proton (go from -NH3+ to -NH2) ​[3]​. Knowing this, is there anything we can do to help make this happen? Is there any hack we can do?

Luckily there is! Remember pH? In the article about pH and tofu posted a few weeks ago, I wrote about how pH is an inverse measure of the number of free protons (a low pH means many free protons; a high pH means few free protons). In that post, we saw how we could reduce the pH (increase number of protons) to disrupt proteins and force them to clump up into tofu.

For pretzels we instead remove protons. We dunk them in lye (NaOH, sodium hydroxide), a high pH solution. This solution has very few free protons and will start to steal protons from everywhere, once again wreaking havoc. In the dough proteins will be destroyed, starches will start to break down and the free amino acids will lose some of their protons. This last reaction is exactly what we are after: depriving the amino acids of their spare protons will make them react with the sugars more easily. It will lower that energy threshold we mentioned in the chemistry brush up above.

Or in (almost) plain English: the lye will make the amino acids more prone to reacting with the sugar and the Maillard reaction will occur faster. As a result, we get significant Maillard reactions even at lower temperatures and short bake times with the characteristic browning and flavour development.

A tasty experiment

While the theory makes sense and a lot of other people have written about it, it is always good to test the theory with an experiment ​[5], [6]​ (especially if the experiment is edible). So I tried making pretzels and dipping them in solutions other than lye. Many recipes simply use baking soda ​[5]–[8]​ instead of lye – it is easier to find and not as dangerous and gives a high pH solution. So I prepared pretzels and dipped them in water with 8% baking soda (pH 10) or 3% lye (pH 12). Since we think the pH is the main factor here, I also tried dipping pretzels in clean water (pH 7) and in acetic acid (pH 3). (Remember that the pH scale is a bit strange (logarithmic). pH 12 has 100 times less free protons compared to pH 10.)

I prepared a simple pretzel dough (recipe below). After letting it rise, I shaped the pretzels and put them in the fridge for 30 min (to dry out a bit without rising further, great tip from The Spruce Eats ​[9]​). Then I dipped them in the solutions, sprinkled them with salt and baked for 12 min at 205°C. The results speak for themselves:

The acetic acid and water did nothing and the Pretzels got almost no colour. The baking soda pretzel got some colour and, while it was tasty, it did not taste like a pretzel, ‘merely’ fresh baked bread. The Lye dipped pretzel unsurprisingly got a beautiful hue and that rich pretzel flavour. Additionally, the pretzel skin is much softer and stretchy where the baking soda pretzel is quite hard and crisp.

An interesting side note, some recipes use baked baking soda ​[10]​. Basically, you spread baking soda on a pan and bake it at 175°C for 2-5 h. This forces hydrogen out and your baking soda is converted from NaHCO3 to Na2CO3, a much stronger alkaline solution. When dissolved in water, you get a much higher pH than with pure baking soda. The resulting pretzels should be better but as I did not try this, I don’t know how it compares to lye-based pretzels. 

WARNING: Absolutely do try this at home but be careful. Both lye and baked baking soda are corrosive and can hurt you. Wear gloves and be careful. Use a glass bowl. When dissolving lye pellets in water, a lot of energy will be released and the water will get hot. Always drop the pellets in water and not the other way around, as the heat released can cause small amounts of water to boil rapidly. Work in a well-ventilated area, the fumes rising from the water are harmful (there is no gas released as such but some vapor will rise and can contain NaOH). I mix the lye pellets into the water in a glass bowl and leave the kitchen for a bit. Not sure how this applies to baked baking soda but be careful. If you get some lye on your fingers, just rinse with water. It feels soapy. Don’t let this warning dissuade you, it is not that dangerous. And the result is super tasty.

Conclusion

Now we have learned a little about the Maillard reaction – the chemical reaction between free amino acids and some sugar which creates the brown colour and the rich flavours in foods cooked at high temperature. We also learned that while the Maillard reaction foremost occurs at high temperature, it also occurs slowly at lower temperatures and is responsible for black garlic, miso and Dulce de leche.

For pretzels, the secret Maillard hack is to increase the pH to force the reaction to occur faster. As a result we get flavourful browning after just 12 minutes at 205°C. This hack can be applied to other dishes as well, you can for instance sprinkle in some baking soda while browning onions to get the Maillard reaction to proceed faster (though I’ve read that the taste is affected) ​[11], [12]​.

I hope you learned something new about kitchen chemistry and feel up to trying to make your own pretzels. It is super easy once you’ve bought some lye and the results are really tasty. Your friends will definitely be impressed.

Print

Pretzels

These simple, classic Pretzels are dipped in 3% lye (sodium hydroxide) for that authentic pretzel flavour. Easy to make and delicious.

Course Snack, streetfood

Cuisine German

Keyword baking, lye, pH, sodium hydroxide

Prep Time 30 minutes minutes

Cook Time 12 minutes minutes

Resting time 1 hour hour 30 minutes minutes

Servings 8 pretzels

Ingredients

Dough

• 1 tsp dry yeast
• 250 mL warm water
• 1 tbsp olive oil
• ½ tsp salt
• 1 tsp sugar
• 750 mL all purpose flour (490 g)
• coarse salt for sprinkling

Lye bath, 3%

• 15 g lye / sodium hydroxide. FOOD GRADE Warning, see note
• 500 mL water

Instructions

Dough

• Dissolve yeast in water.
• Add salt, sugar, and oil.
• Work the flour into the liquid. The dough will be very dry and firm but it works.
• Let rise for 1 h.

Pretzels

• Divide the dough into 8 equal parts. Roll them out into long strands with a thick center, all pieces at once.
• When you have rolled out the last one, start with the first piece and roll it out again. This has ggive the dough some time to relax and makes it easier to form. (You may see that the rolled out strands shorten during relaxation.)
• To make the pretzels, twist the dough ends about each other and fold them back onto the thick part. I like to add a little water between the dough pieces here to help them seal.
• Move the pretzels to a tray lined with a baking sheet. Let rest in the fridge for 30 min to dry them out a little. This makes them easier to handle.

Dipping and baking

• When the dough is resting, prepare the lye solution. Pour the water in a glass bowl and carefully add the pellets. Stir and wait for them to dissolve. Wear gloves and be mindful of the fumes. See warning below.
• Once the pretzels have rested, dip them into the lye and fish them out again. I use a silicone slotted spoon but anything will do. Wear gloves.
• Move the dipped pretzels onto a baking tray with a baking sheet and sprinkle with coarse salt.
• Bake for 10-15 min at 205°C.
• Enjoy with beer and mustard.

Notes

WARNING: Absolutely do try this at home but be careful. Lye is corrosive and can hurt you. Wear gloves and be careful. Use a glass bowl. Wear gloves. When dissolving lye pellets in water, a lot of energy will be released and the water will get hot. Always drop the pellets in the water and not the other way around, as the heat released can cause small amounts of water to boil rapidly. Work in a well-ventilated area, the fumes rising from the water are harmful (there is no gas released as such but some vapor will rise and can contain NaOH). I mix the lye pellets into the water in a glass bowl and leave the kitchen for a bit. If you get some lye on your fingers, just rinse with water. It feels soapy. Don’t let this warning dissuade you, it is not that dangerous if you’re a little careful. And the result is super tasty.