WTF? - What's the Foam???

[RedtailForester]

I had something very odd happen while making a batch of rocoto sauce the other day. After I had initially cooked and blended everything, I started to reduce it a bit. After a few moments, foam started to billow out of the sauce and continued to do so until I bottled it. My original concern was some residual soap had been in the pot but after tasting the sauce, that couldn't be it.

I read somewhere that using certain thick walled varieties may have a lot of air stored in their flesh.

Has anyone else ever had something like this happen?

 

[Justaguy]

When I boil down I get that a good bit with some of my sauces especially my watermelon sauce. I have to constantly stir it to keep them down until the boil goes for about 10 minutes, then they die down. From what I have gathered it is the stored air in the liquids other then plain water.

 

[Smiter Q]

As sauces reduce, the liquid becomes more viscous. So instead(or in addition) to large bubbles, the bubbles become smaller and can not agitate to a "pop" as easily in the heavier liquid as the big ones do, hence the foam. I started making jelly recently, and this happens a lot in jelly making as it is a pretty thick liquid when using pectin or pectin based fruit. In jelly making some folks add a tablespoon of butter or oil to cut down on the foam, and some do not. Although you may not be using added pectin, it is in the plant cell walls of the pepper to a degree. Seems you are making a thicker reduction which is why the foam happens. Hope this helps.