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Scum on Home-made Soup

by Clive V. Lewis
(Chesham.Bucks. U.K.)

Clive's question...

My lunchtime habit is to make a 'soup of the day'. It may be lentil/vegetable - or whatever is handy. I have noticed that (for want of a better word) a "scum" forms on the surface, which I skim off.

Taking an analogy from the iron/steel-making business where metal is heated to melting point - a similar deposit forms on the surface, and, being impure is rejected.

So, has anyone analyzed the deposit which forms on the surface of soup and if so, is it deemed to be unhealthy. I notice that onions in particular contribute significantly, although there appear to be lots of good things in onions.

I've often wondered about this & thought that you may have some ideas. Curious!

Tks ... Clive

Suzy's answer...

Hi, Clive!

What an interesting analogy between steel making and cooking soup!

A collection of protein

My understanding of soup-making is that the foam, or "scum" as you call it, that develops while soup is simmering comes from proteins (and possibly some fat, depending on the type of soup you are making) that congeal and collect at the top of the soup.

I can't find any research to suggest that it is anything harmful, but many people do skim for various reasons.

Clear and not cloudy does not just refer to the weather!

Certain types of stock and consomme are supposed to have a particular clarity when they are served. To obtain that quality, they are skimmed throughout the cooking process. Soup
connoisseurs will tell you that the clearer broth also tastes better.

In Japanese cooking, skimming the surface of the soup is very important to create a "clean" soup. It is extra work, but Japanese cooks feel it is vital to obtain the proper taste and to keep the liquid clear.

What I do...

Personally, I do not skim most soups, because I want to keep those nutrients in the soup, but it is probably a matter of personal taste. The one exception for me is when I make French Onion Soup. I have an old Russian recipe that makes an excellent product, and it says to skim the foam, so I skim, for no other reason than that the recipe tells me to do it!

Stay tuned...

Having said that, if you or any of our readers ever come across information about tests being done that determine that there is a good reason other than the appearance of the soup, such as the presence of bad actors in the "scum," please contact me. I would be very interested to hear about it! (Using the words "scum" and "bad actors" in a sentence makes it seem like we are writing bad crime fiction here, not talking about cooking!)

In the meantime, Clive, your daily soup sounds delicious and nutritious, so skim away or don't skim as the mood takes you, unless you are making consomme for a connoisseur, of course!

Thanks for visiting our website and stay healthy with my warmest regards,


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