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I read many recipes of pretzels and they required to dip the raw dough in a bath of lye. As anyone should know for their own safety, lye is caustic and shouldn't be ingested.

What is the process involved that make them edible?

Edit: I am aware of the action of the lye. I wonder how the non-edible lye on the dough is transformed into something that is safe to eat.

  • 25
    The difference between medicine and poison is the dosage. Neither Sodium (present in salt) or OH- (present in water) are inherently toxic. So lye in low concentration causes no harm. This question seems to assume any quantity of lye is hazardous. – Mindwin Mar 28 '17 at 17:43
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    Related question on Chemistry.SE – Mindwin Mar 29 '17 at 13:51
  • @J... Part of the lutefisk preparation from link you give is "To make the fish edible, a final treatment of yet another four to six days of soaking in cold water (also changed daily) is needed". Pretzels don't need to be washed for days before eating. So while the fundamental answer is the same ("lye is used in preparation, but you don't eat significant amounts"), the processes aren't that similar. – armb Mar 31 '17 at 13:36
  • YouTube: Using Potassium Hydroxide as a Condiment. I actually use potassium hydroxide (KOH) for my pretzels because I have a bottle of it for hydroponics, but not NaOH. – Nick T Apr 2 '17 at 13:42
  • We natively have a safe dose of a potent corrosive (hydrochloric acid) in our stomachs... – rackandboneman May 10 '18 at 22:46
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Basically, the lye reacts with the CO₂ and moisture present during baking to form a non-toxic carbonate. This makes it safe to eat.

The reaction:

CO₂ (g) + H₂O (l) ­⇄ H₂CO₃ (aq)

H₂CO₃ (aq) + 2 NaOH (aq) → Na₂CO₃ (aq) + 2 H₂O (l)

From here (MS doc)

[EDIT]

Spurred by the comments, I have searched further.

tl;dr There is much going on wrt the lye dip. As far as safety goes, the lye is consumed in many reactions, including the above.

  • (Firstly: The equation source was not the basis of my answer; rather it was to refresh my memory of the reaction about which I was told/read several years ago was the reason why lye is safe to use on leavened breads, which was its combining with carbonic acid. (I apologize for not checking the balance adequately.)
  • My recent search only found one reference at The Kitchn to the reaction of lye with carbonic acid as the reason for its safe use. It is also unsourced.
  • Simultaneously, I found a research paper and a Food Chem Blog entry which referenced it, both of which discussed the behavior of the lye bath on pretzels. There is a lot there, so I shall only quote the paper abstract:

The effects of alkali dipping on starch, protein, and color changes in hard pretzel products have never been researched. Experiments were conducted to mimic reactions occurring on the pretzel dough surface. Dough was dipped in water or 1% sodium hydroxide solution at different temperatures between 50°C and 80°C. Protein and starch profile after dipping were analyzed. Color development on pretzel surface following the extraction of pigments from flour was investigated. Whole dough and pretzel samples were also made at pilot plant and the properties were analyzed. Only starch granules on the dough surface were gelatinized following dipping. Amylose-lipid complex dissociated at a lower temperature with alkali treatment but were not dissociated, even at high-temperature dipping in water. Treating the dough at 80°C in alkali solution resulted in the hydrolysis of proteins into smaller peptides that could be not precipitated by trichloroacetic acid (TCA). Dough surface color was different following pigment extraction from flour but not significantly different following baking. The results suggest that the color that developed on pretzel surface was not due to pigments present in the flour but was contributed by the reaction within or between the starch and protein hydrolysis derivatives during baking.

and what I think is the pertinent quote from the blog:

The protein results (2 in the list above [reproduced following]) indicate that the lye dip provides the smaller proteins needed for Maillard reactions, whereas the water dip does not. This seemed like perhaps the most important point to me.

  1. The dip resulted in the hydrolysis of protein into smaller peptides. This happened a little bit in 25°C water or lye dip, more in 80°C water, and a lot more in 80°C lye dip. Also, the smaller peptides in the hot lye dip had the smallest molecular weights; most of them “walked off” the electrophoresis gel, leaving no bands. The authors explain that the alkaline conditions of the lye dip result in like charges along the proteins, which repel and cause the proteins to unfold; this makes them more susceptible to hydrolysis.

Both the blog and the paper are worth reading.

My conclusion: the lye is consumed by the various reactions and therefore poses no safety concerns.

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    I don't think this reaction is correct or relevant. Your quoting from an experiment that puts a solution of sodium hydroxide in a PET bottle filled with pure carbon dioxide (CO2), which is nothing like the environment pretzels are made in. The final equation also looks wrong as its not balanced. It was probably meant to be NaOH + H2CO3 -> NaHCO3 + H2O. That product, sodium bicarbonate (NaHCO3) wouldn't be desirable on pretzels, as it without an acid present it would breakdown to sodium carbonate when baked (2 NaHCO3 -> Na2CO3 + H2O + CO2), and give the pretzels a bitter soapy taste. – Ross Ridge Mar 28 '17 at 23:18
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    @RossRidge I'll go a little farther. The claimed reaction is just wrong precisely because it doesn't balance: one atom of hydrogen just disappears. Chemistry department fail. On the other hand, there's not much lye so it's plausible that the relatively high temperature and the fairly CO2-rich atmosphere from the fermenting yeast is enough to make the reactions you describe happen. Note that lye is already turning the fats in the dough literally to soap, so maybe a soapy taste isn't significant. – David Richerby Mar 29 '17 at 8:44
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    Balancing the equations is good, but there's still the bit where this doesn't seem a likely reaction - I know there's a bit of water on the surface of the pretzels initially, but they dry pretty fast, so there's really not a lot of chance for the first reaction to take place. Do you have a source specifically saying this happens in pretzels, not just the more artificial conditions described in your link? – Cascabel Mar 29 '17 at 15:03
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    And another problem. Even if this reaction is possible, what would be the point? You're proposing that the lye gets neutralized by being converted to sodium carbonate. OK, fine. Why do you want sodium carbonate on your pretzels? Because, the way you write it, the only purpose of the sodium carbonate is a neutralization product of the lye. But if that's the only reason, there's a much easier way to deal with the lye -- just don't dip the pretzels in it in the first place! – David Richerby Mar 29 '17 at 23:03
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    It's not the most solid, but On Food and Cooking does have this: "The starch gel hardens to a shiny finish and thanks to the alkaline conditions created by the lye, browning-reaction pigments and flavor compounds rapidly accumulate. (The lye reacts with carbon dioxide in the oven to form a harmless edible carbonate.)" @DavidRicherby Well, conceivably the effects on the proteins are the desired effect and carbonate is formed as a byproduct. – Cascabel Mar 30 '17 at 15:00
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The purpose of dipping in lye (or other basic solution, like baking soda...or even baked, baking soda) is that it promotes coloring, as the solution reacts with the surface of the dough. It also promotes the Maillard reactions when the dough cooks. The result is even browning and that typical alkali flavor. If choosing lye, food grade is important, as commercial grades may include other, heavy metal, impurities. Lye is extremely caustic. So it must be used carefully! In pretzel and bagel making the solution is generally quite dilute...maybe around 3% lye in water. In both pretzel and bagel making, the product is typically given a brief bath in boiling water, after a dip in the lye solution. The boil and/or subsequent baking neutralized the alkali rendering it safe to eat.

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    @A.D. Caustic compounds are edible when diluted sufficiently. Now I haven't done the math to see if 3% lye is already OK, and there is certainly also a reaction between the lye and the dough, but if you were not aware that dilution matters (and you seem not to) then this answer adds an important detail. – rumtscho Mar 28 '17 at 16:55
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    This doesn't answer the question that was asked. – Ryan Cavanaugh Mar 28 '17 at 18:23
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    Boiling doesn't neutralize alkalis. – David Richerby Mar 28 '17 at 21:14
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    Here in Germany (pretzel country) the pretzels are never boiled or rinsed after their stint in the lye. – Stephie Mar 29 '17 at 7:41
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    Seems likely that most people think of caustic compounds in light of what they've seen in cinematic effects. I.e. as if every strong acid or base were either some kind of universal solvent or a catalyst. E.g. the Alien movies. – can-ned_food Mar 29 '17 at 11:20
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The reason it is safe is three-fold.

First, the concentration is only 1% NaOH and the pretzels are only dipped for 10 seconds (see Snack Food Technology pages 180-182) which limits the amount of hydroxide per pretzel.

Second, the dough itself, for example protein of the dough, has acidic groups, such as amino acid side chains of lysine and tyrosine, which neutralize the hydroxide.

Finally, as explained in Effect of Alkali Dipping on Dough and Final Product Quality Journal of Food Science vol. 71, pages C209-C215, protein in the dough is partially hydrolyzed under the alkaline conditions. This exposes more terminal amino acid groups which also participate in neutralization.

The Snack Food Technology book cited above also explains:

If the caustic concentration becomes too high, there is not a complete conversion to sodium bicarbonate in the baking and drying cycles and the pretzels will be hot to the taste due to the residual sodium hydroxide

  • Actual science at last! Thank you! (And the word "carbonate" doesn't occur anywhere in the linked paper.) – David Richerby Mar 30 '17 at 15:09
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    @QueueHammer Late answers always suffer. The accepted answer already had 30+ votes by the time this one was posted and it will get more votes in the future, simply by being the first answer that people see. – David Richerby Mar 31 '17 at 7:54
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    @Jefromi supposing it is converted to bicarbonate initially, it would still eventually be converted to carbonate upon baking due to thermal decomposition. This 1948 source says the lye is changed to carbonate books.google.com/… – DavePhD Mar 31 '17 at 16:55
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    @Jefromi Principles of Cereal Science and Technology says "bicarbonate" and that it forms due to reaction with CO2 from air. books.google.com/… – DavePhD Mar 31 '17 at 17:07
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    Typical Lye used for German "Laugengebäck" ("Lye-Bakes") such as Pretzels is around 3%. Your answer is still correct, but the original concentration is three-times higher than stated in your answer. – user2705196 Apr 1 '17 at 16:16
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Lye will readily react with either amino-acids (producing respective sodium salts) or with fats (producing soaps), both reactants being readily present in dough. You don't need CO2 to neutralize it.

Ingesting small amounts of those end-products is indeed safe, and normally only a small quantity of lye is used in the process.

  • +1. Consider what NaCl + H_2O forms. You can, in fact, consume pretty high concentrations of lye as long as the result isn't caustic when it touches us. Nobody whines that there is lye in Gatorade. – The Nate Apr 1 '17 at 16:44
  • @TheNate I don't understand what you mean by "consume pretty high concentrations of lye as long as the result isn't caustic when it touches us." Lye in high concentrations (actually, even in fairly low concentrations) is caustic; consuming requires touching. So how can I consume pretty high concentrations of lye without touching anything caustic? – David Richerby Apr 2 '17 at 14:54
  • @TheNate And Gatorade doesn't contain lye. At least, it's not on the ingredients list (go to the "nutrition" tab; no direct link available). – David Richerby Apr 2 '17 at 14:59
  • NaOH is lye. They would have added salt, which then disassociates in the water. NaCl + H_2O dissociates into NaOH and HCl. Hence, it's both present and not on the ingredients list in lots of places. If you're concerned about the lye, just make sure to eat it with mustard so the vitriol can neutralize it before it goes inside you. – The Nate Apr 2 '17 at 22:35
  • @TheNate NaOH + HCl is not the same as NaOH alone. Nothing will happen if you put your finger in table salt, but in lye your skin will melt pretty fast. Of course, Na is not toxic, so you can say "It's OK", but you'll still lose your finger. – Dmitry Grigoryev Apr 3 '17 at 7:37
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The references noted above have mostly looked at the specific chemical changes to the constituents of the dough and the species in solution. A few point to the Maillard reactions as a contributor to what is going on.

It is worth noting that the Maillard reactions are quite complex and involve a lot of intermediate products. However, in many cases the rate limiting factor is the pH of the constituents. It is possible to accelerate the reactions by raising the pH, and more Maillard products are produced if you let the process run for an extended period of time or raise the temperature which further increases the reaction rate. Some people don't believe that you can get the reaction to go at all at temperatures below 300°F, yet adding a little baking soda to a batch of onion soup and pressure cooking it (265°F) for 40 minutes will yield the same browning that much longer cooking of the onions produces in the classic technique.

So increasing the pH by using lye (pH 13) vs sodium carbonate (pH 10) vs sodium bicarbonate (pH 8) will facilitate a dramatic speed up the Maillard reaction rate, and subjecting the pretzel to high temperature in the oven will carry it out. What happens to the NaOH to detoxify it is most likely a combination of neutralization, dilution, and chemical conversion through interaction with other available species. I would not recommend eating dough dipped in lye without baking the dough first.

I am intrigued by the notion that the high pH breaks down the proteins into shorter amino acid sequences which facilitates the Maillard reactions but does not affect the rate constants.

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