Limestone Paste?

Hello guys. I am a Thai food enthusiast here and would like to know if any of you are familiar with (red) limestone paste?

Thais use this thing a lot by mixing it with water then wait for the whole solution to separate into two layers: clear water and limestone sediment - this 'clear water' is then used in many recipes, especially for making crispy, deep fried sweets and savouries, and even soaking fruits and vegetables in it prior to cooking to make them stay 'firm' as well as having an interesting texture when you bite into them, it is as if they have a thin outer shell.

I am currently living in London and it is so difficult to find limestone paste.. I was wondering if you guys know of any good substitute for it? Also interested to know the science behind it as well, if possible!

Cheers

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matthewmicahhall

I would recommend finding a source of pickling lime. I just found something called "Mrs. Wages Pickling Lime" on amazon.co.uk -- this should presumably work.

In short, you are harnessing the magic of calcium hydroxide to get the firming effect. Calcium hydroxide is sparingly soluble in water. This is why you get two layers forming with the limestone paste -- only a small amount of calcium hydroxide dissolves to produce calcium ions in water. The calcium ions that are released can now diffuse into your fruit/vegetable and interact with pectin, a structural component of the cell walls. The calcium ions cross-link the pectin chains together into a stronger network.

pnicha.k

Wow thank you so much, Matthew. I am ordering it on Amazon right now

GaryT_92514

Thanks for the explanation. Would that mean that more soluble calcium salts (calcium lactate/chloride/gluconate) would have a similar effect? Or, does the OH- have a role... does pH matter?

matthewmicahhall

Good question -- yes, the more soluble calcium salts can also provide the firming effect, but your choice of a calcium source can have consequences. I'm not an expert on this, but here is my understanding of the common options:

Calcium hydroxide -- You will frequently see recommendations that hydroxide-treated foods be soaked in several changes of fresh water to remove excess calcium from the initial treatment. I think what they really mean is the excess OH- ion, which will in fact alter the pH. This is particularly important if you intend to pickle the food since the OH- will neutralize some amount of the acidity that you need for actual preservation of the product.
Calcium chloride -- This is frequently used as an alternative to calcium hydroxide for firming up pickles since it doesn't contribute to the pH problem (look up a product called "Pickle Crisp"). I know that overdosing with calcium chloride can impart a bitter taste. Other substances like sodium chloride and sugar can help offset the bitter flavor.
Calcium lactate/gluconate -- The calcium lacate/gluconate salts are interesting because they do not have either of the aforementioned problems (increasing pH or bitterness). I found this online article if you're interested in learning more. Calcium lactate/gluconate is generally a little more expensive, although Modernist Pantry is selling 50 g of calcium chloride and calcium lactate for the same price (calcium lactate gluconate is a little more expensive).
Other options include calcium sulfate and various calcium phosphates. I believe that they can contribute to off flavors as well.

GaryT_92514

Thanks Matthew - very helpful reply. I've tried a couple of the Mugaritz recipes that use calcium hydroxide (the pumpkin was my favourite). It will be interesting to try again with lactate/gluconate. Interesting article too.