Tuesday, April 10, 2007

eletro-chemical chicken stock acid test

If you have not done so already, you can add pH to your list of things to worry about before you make stock.

The glasses in the photo show five samples of one batch of chicken stock. I adjusted each to a specific pH with either lemon juice or sodium bicarbonate (baking soda) so that pH of each rises from left to right.
The most striking thing you notice is that the color darkens as the alkalinity of the stock increases. There were also significant differences in clarity which did not come across in this low resolution photo: the more acidic samples were more cloudy.
None of this surprised me as it was all predicted by the science of the electro-chemistry of colloidal systems. But it's certainly worth running up the blog pole as a caution to anyone who is tempted to jazz up their stock with acidic ingredients like vinegar, lemon or canned tomato.

The net-net?
For optimum color and clarity the pH of all the ingredients in your stock should be as close to pH 7 (neutral) as possible.


Anonymous said...

Very cool. What were the differences in flavor? Also, what kind of PH monitor do you use?

Bob del Grosso said...

There were obvious differences in taste across all samples. The alkaline variants were bitter, and the more acidic versions tart. The alkaline samples also had a funky musky aroma.
I use an inexpensive consumer type pH meter from Hanna Instruments. It's not the greatest but it's cheap and fine for the kinds of tasks I ask it to do.
This is the one I own:

Stephen said...

Given this test was done on chicken stock, I guess my question is then why does almost the opposite effect happen when making a Consume?

the raft must include some kind of acidic element. Does the clarity result from the right PH level or is it offset by something else in the raft that prevents the cloudyness?

Bob del Grosso said...


Consommé behaves the same way. if you make the raft material too acidic the color "fades" and the clarity goes south. thing is, even if you put tomatoes in the raft material the pH is still going to be pretty close to 7.

Check this out: in the old days chefs used to use egg shells in the raft material. Then after it became known that it was the egg proteins that were responsible for clarification the habit of using the egg shells mostly disappeared.

Well, egg shells are alkaline and if you include them in the clarif it bumps the pH of the consommé up over 7 and the finished product is darker and more clear. I know this bec. I tested with my class at The CIA many times.

The Foodist said...

Thanks for the answer. Figured it was as much with the PH Level being equal.

Ive always noticed a difference in clarity when using a canned tomato as the acid vs using a Vinegar or other acidic element in Consomme (I really shouldnt try to spell so late at night).

Many of my chefs at CIA have mentioned the egg shells, but never explained why it faded out of use, thanks for the clarification.

...ok no more bad consomme jokes.