Any chemists here? Would like to synthesize sodium citrate in a pinch.

[Obuibo]

I don't have immediate access to any sodium citrate at the moment, but I'd like to try emulsifying cheese a la Modernist Cuisine.

It's come to my attention that it's possible to synthesize it with an aqueous solution of citric acid (which I can cheaply find at any grocery store) and the addition of sodium bicarbonate. I'm assuming the visible reaction is just the release of carbon dioxide, but I'm just guessing. I'd really like to know if this is food safe and, if so, what proportions should I use to avoid undesirable amounts of reactants and reagents? Also, would it be stupid to use beer instead of water.? I don't know what else is in beer aside from water and alcohol, and I'd really prefer not to hurt anybody

[gfweb]

The solution is probably dissolved sodium citrate (check the label). If that's the case you could just evaporate it to get the Na-citrate. Or maybe just calculate how much of the soln you need to match the amount of citrate in your recipe.

[Got49]

Obuibo,

you are right that you can synthesize sodium citrate from citric acid, using baking soda, and the bubbles you are seeing is CO2. it is a 1 to 1 molar ratio of citric acid to baking soda, I can't give you the exact values because that depends on the concentration of the citric acid. I can also tell you that if you are using water as your solvent It is going to take a long time to evaporate it away and you are almost certainly not going to have a pure product. The product SHOULD BE food safe if you are starting with food safe since you will just be neutralizing the citric acid.

Hope this helped

[huiray]

Citric acid has 3 carboxylate groups. A 1:1 citric acid/baking soda mixture will give you monosodium citrate. Is the commercial or MC "sodium citrate" the monosodium citrate, or the (more probable) trisodium citrate? In any case, cessation of "bubbling of CO2" is not indicative of one reaching the end-point of the titration, it can be misleading because this acid-base reaction is not the "strongest" in the class and CO2 has appreciable solubility in water. Also, the extent of hydration and purity of the two components will have an impact on the actual weight of the two substances you need to add together because the effective molecular weights of the substances will be affected.

Edited October 31, 2013 by huiray (log)

[pbear]

To confirm, yes, the procedure described in the OP will produce monosodium citrate, whereas the product called for in Modernist Cuisine is trisodium citrate. The former works well enough, but the latter works better.

[Sharif]

Well, as has been noted, you probably want trisodium citrate. In fact, you probably want trisodium citrate dihydrate (rather than the anhydrous version, but the difference between the two is only about 14% by weight) as this is what is normally intended by sodium citrate.

Basic recipe: if you want 100.0 grams of sodium citrate, then you'll need 85.69 grams sodium bicarbonate (i.e., baking soda) and 71.45 grams citric acid (which I assume is monohydrate; if you know you have anhydrous citric acid, use 65.33 grams instead) and dissolve them both in water. There will be lots of CO2 bubbles released so you may want to add things in slowly.

If you are making the sodium citrate for immediate use, then it's usually easy enough to just add 85.7% baking soda and 71.5% citric acid to your cooking liquid in place of 100% sodium citrate and continue with your recipe. I wouldn't recommend doing this directly in milk (use some water/beer instead and add the milk later) since the bubbles will foam the milk up and get unruly. This reaction technically adds a bit of water as well (12.25% of the sodium citrate weight) but this is usually < 0.8% of the total liquid in the recipe assuming the usual concentrations of sodium citrate so is likely negligible.

If you want a powder for later, you just need to boil the water off. To get the dihydrate form, keep the solution below 158 C/316 F. Putting it in the oven at around 300 F should work. Breaking it up periodically as it is drying can help to get a powder in the end.

- Sharif