The Use of Limestone Solution (น้ำปูนใส) in Thai Cooking


limestone in thai cooking
Limestone (more accurately slaked lime) solution is traditionally used in quite a few Thai recipes. The same limestone paste with a curiously pink hue was part of the betel chewing culture in the olden days and, therefore, a household ingredient. Tinted limestone paste (pun daeng or ปูนแดง) is mixed with water and left undisturbed to allow the limestone particles to settle at the bottom thereby creating a clear separation between the limestone itself and the translucent solution. It’s the alkalinity of the clear limestone solution that Thai cooks have used to create enduring crispness in fried batter or pastry/dough as well as firm, crunchy texture in pickled or candied fruits or vegetables.

limestone in thai cooking
Here are some facts about the kind of limestone used in Thai cooking:
* Limestone solution or limestone water is solution of a chemical compound whose chemical name is Calcium Hydroxide (Ca(OH)2).

* Limestone is made from creating Calcium Oxide (CaO) from Calcium Carbonate (CaCO3) through heat. Calcium Oxide, also known as unslaked lime or quick lime, is dangerous. It needs to be slaked with water first in order to be used in food. Slaked lime after evaporation becomes Calcium Hydroxide, a white powder.

* When this white powder is mixed with a small amount of water, it creates a paste that is used in betel chewing. The pink hue you see in pink limestone paste (ปูนแดง) is derived from an addition of turmeric. Adding turmeric to limestone achieves two things:
1. The acidity of turmeric offsets the alkalinity of limestone making it safer to chew.
2. Betel chewers generally regard the addition of turmeric as an improvement to the taste and fragrance of limestone paste. The pink color, therefore, is only an unintentional byproduct created by the interaction between turmeric and limestone.

limestone thai cooking
* This means that you can benefit from a solution of water and Calcium Hydroxide in white powder form (food-grade lime) in the same way you would from the pink limestone paste used in Thai cooking (unless your purpose is to chew it instead of using it in a recipe). There’s nothing magical about the pink limestone. The reason some Thai recipes specify pink limestone solution is because that’s the most common form in which Calcium Hydroxide exists in our culture when it comes to cooking.

* The saturation point of limestone solution is 1.5 grams of Calcium Hydroxide per one liter of water.

* If you can get a hold of Thai-style pink limestone paste (available in Thai or Southeast Asian grocery stores, both brick & mortar and online), just mix the paste with enough water to create a saturated limestone solution. What you’ll get first is a pink, cloudy liquid. It should take about 30 minutes for the limestone particles to sink to the bottom of the container. The clear solution is what you use in the recipe.

* Limestone solution prepared this way can be kept in a glass jar, at room temperature, for close to a decade! Once the limestone has lost its potency, you need to add more of either the traditional Thai pink limestone paste or food-grade lime powder to the solution.

* You know when limestone solution has lost its potency when:
1. After a vigorous shake, the limestone particles sink to the bottom immediately. Once shaken, potent limestone is supposed to stay suspended for at least 20 minutesbefore sinking to the bottom.
2. When not in use, limestone solution that is still potent will have tiny white flakes floating on the surface. The absence of these little white flakes means the limestone is no longer suitable to use in the recipe.

limestone used in thai cooking
In the past, I have introduced a few batter-fried dishes to you wherein limestone solution would have been used. Instead, a mixture of some form of liquid and baking soda is called for. This is because baking soda, when mixed with water, represents the closest thing to limestone. The two are not interchangeable as baking soda or Sodium Bicarbonate (NaHCO3) does not exactly replicate the effects of limestone, and cannot be used with success in some applications in which limestone solution is used, e.g. pickling liquid. But in the case of batter-fried dishes, baking soda, thanks to its alkalinity, can be used to achieve an acceptable level of the much-desired crispiness and lightness.

25 Responses to The Use of Limestone Solution (น้ำปูนใส) in Thai Cooking

  1. Rick August 4, 2010 at 12:05 am #

    Quite interesting

  2. prettyPeas August 4, 2010 at 4:10 am #

    The pictures really make me want to try the pink limestone. That, and I love crunchy fried food. Is it right to assume you need just a teaspoon or so in your batter?

  3. Leela August 4, 2010 at 1:39 pm #

    prettyPeas – Actually, no. Limestone solution (the clear water you get after the limestone particles have settled, not the limestone itself) replaces the fat-free liquid (most of the time water or seltzer or carbonated water) which the batter recipe calls for. For example, if a batter recipe calls for 1 cup water and 2 teaspoons baking soda, you can replace both with 1 cup of limestone solution.

  4. rapier August 4, 2010 at 7:28 pm #

    While I think this is a fascinating entry I’m disappointed because it doesn’t actually say how one would use limestone solution in various recipes and it doesn’t indicate why it’s better than baking soda. Your insights and knowledge are formidable but this post, to me at least, lacks context.

  5. Leela August 4, 2010 at 8:22 pm #

    rapier – This post is part of the Thai pantry series in which I introduce different ingredients used in Thai cooking, most of the time without including any recipes. It’s sort of like the introduction to ingredients you find at the beginning of most cookbooks. It’s the subsequent recipe posts, to be linked up with the pertinent ingredient posts, that will tell you how and how much such and such ingredients are used.

    I got a lineup of limestone-related recipes planned for the future, and the information on the way in which limestone is used as well as how much will be part of each of those recipes. The purpose of this post is to introduce an ingredient so that I won’t have to repeat any of this every time I write a recipe that calls for limestone.

  6. OysterCulture August 5, 2010 at 6:53 pm #

    This is so Harold McGee – love it!

  7. Gera @ Sweets Foods Blog August 5, 2010 at 8:27 pm #

    I had a doubt when a kid if to choose chemistry or engineer, chose the last, but in my heart adore all the chemical process in everything, more in food. I didn’t know about limestone and less its chem-properties… very interesting!! :)

    Cheers,

    Gera

  8. Dorrie August 7, 2010 at 3:48 pm #

    Interesting post!

    Is this limestone also used to preserve my so much loved 100-years-old-eggs?

  9. Leela August 7, 2010 at 4:59 pm #

    Dorrie – Yep. Calcium hydroxide (not in the turmeric-tinted form like this, though) is what is used to make those eggs.

  10. Vernassa4 December 27, 2010 at 11:53 pm #

    so–Leela–for the 1 cup of solution of water and lime paste that you might use to replace the 2 tsp.baking soda and cup of liquid, say water, in a given recipe would you use 2 tsp also of stiff lime paste? Approximately?

    Just bought some paste at the Rice and Spice for fun.

    Thanks!

  11. Leela December 28, 2010 at 1:20 am #

    Vernassa4 – actually, you never want to use the actual limestone paste in the recipe. What you want to use is the clear solution that you get from mixing the paste with plain water and after the paste has sunk to the bottom of the jar. I’d dump all of the limestone paste you have bought into a glass jar, mix it with plain water (about 2-3 times the amount of limestone paste), shake the jar, and let the paste sink to the bottom. Then measure out a cup of clear liquid to use in a recipe. Keep the limestone in the jar like that and replenish the water as needed.

  12. OnKneesforJesus April 14, 2011 at 10:14 pm #

    Thanks for this entry. There’s almost no writing online about the use of limestone in SE Asian cooking. I just tried to make banh lot (Vietnamese name for lod chong) and the Vietnamese recipe calls for limestone water.

    A Viet lady told me that the limestone water will make the lod chong noodles “crispier” but I’m trying to understand what that means. The noodles themselves are chewy, soft, and wet. How can limestone make them more “crispy?”

  13. Leela April 14, 2011 at 10:34 pm #

    OKFJ – I’m actually testing/refining a recipe for log chong, and I’ve indeed found that the use of limestone solution really does help create lod chong that holds its shape better (after being boiled) and has a better, chewier texture (instead of doughy, soft, and mealy).

    This is kind of like noodles. Noodles made with alkaline solution similar to limestone solution, according to the old Chinese tradition, is more “bouncy,” for lack of a better way to describe it.

    So I think “crispy” is not the right word. The idea that the lady wanted to communicate could be that limestone solution creates the “bounciness” of the finished product.

    All you have to do is follow the recipe that you have, replacing the liquid in the dough with equal amount of limestone solution. That should do it.

    • Michael Malone November 3, 2013 at 4:29 pm #

      Leela I have enjoyed your posts a lot ! As a person who love International cooking I find that in each ethnic class of cooking secrets come out that can be used in all types of cooking. Crisp is Crisp in every country of the world. I found a “cheaters” recipe for KFC and of all places for it to originate…. the West Indies !! The combination of herbs and techniques was so UN-USA, but, so much KFC. Again… thanks for sharing your experiences. Michael in Orlando

      • Leela November 3, 2013 at 4:36 pm #

        Michael – And you will share that recipe from West Indies with me, won’t you? ;)

  14. Theresa January 25, 2012 at 10:58 pm #

    Good information that I could not find anywhere else on the net. I have pickling lime and wanted to know if I can use it to make limewater for these noodles:
    http://lifeinmexico.wordpress.com/2009/11/17/noodles-oh-how-i-love-thee/

    Yes I can! Thank you!

  15. tjbroccoli March 17, 2012 at 9:07 am #

    If turmeric (ka-min) and slaked lime (phun) actually go well together (in that they are a good mixture for making a betel chew), why is the Thai saying “ขมิ้นกับปูน” (“turmeric and slaked lime”) used to describe things that are incompatible, like fire and water? Much thanks.

  16. Admin March 17, 2012 at 1:08 pm #

    tjbroccoli – The saying is based on the fact that when two strong entities come together their differences create a reaction — often one that weakens each other. You put two bullheaded, opinionated, vocal personalities together, you’re bound to see how they affect each other ways that are visible to others. This is the case when turmeric meets slaked lime. It’s true that the reaction between the two ends up serving the betel chewer well, but the saying doesn’t focus on that aspect. It’s about the reaction. This is how I see it.

    Good question.

  17. tjbroccoli May 24, 2012 at 9:33 am #

    Thank you very much for your response, Admin (Leela?).

  18. lou June 27, 2012 at 9:29 pm #

    Hi, for one tablespoon of the paste, about how many cups of water(room temperature or hot water)?

  19. Admin June 27, 2012 at 9:34 pm #

    lou – For a small amount of paste, 1 part paste: 5 parts room temp water has worked for me.

  20. Lauren toenniges July 21, 2012 at 10:56 pm #

    Thank you! I couldn’t find a single thing about practical uses for this magically suspicious paste I had found that didn’t involve betel nut chewing! I’m so excited to use my new information, I feel like I have some kind of super culinary secret now!

    Thanks again!!!

  21. Anonymous August 7, 2012 at 11:02 am #

    I recall my mother, from her mother before her (european), used lime water to help preserve the shape of – comquats, limes, mandarins, figs, olives. She would boil them in spices and sugar as they would simmer and become preserved table sweets in there own syrup. These were served on a hot day with chilled tangy lemonade or ice cream. I do these today, the tradition lives on.

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