Hi guys, got a crowdsourcing question for everyone. This is pretty much a copy of a post I made on a brewing forum because I want to crowdsource it to as many people as possible....
First some background.
Chymosin is the active element in rennet that allows milk to curdle quickly and separate the fatty curds and the liquid whey cleanly.
Apparently plenty of plants have it: common plant ones include figs (it's in the sap), nettles and mallow.
My success with vegetable rennets has not been that good so far; I've tried a couple of times. I've tried fig sap a few times - the milk does curdle - but very slowly, it apparently takes a day for the clean curdle to happen. (Not sure why).
I'm currently trying to curdle milk (for haloumi) with nettle rennet. What you do is boil nettles in water, stir in a bit of salt (which apparently helps bring the chymosin out), and strain the nettles off. Then proceed as normal with the cheese. My milk is currently uncurdled; I've made three additions of nettle rennet over the past two hours - first at eight, the second at nine when no curdling was evident, the third at ten, still no curdling evident. I think the problem I'm having is that the nettle rennet I made was relatively weak (didn't use many nettles), rather than that I haven't isolated the chymosin or my cheese culture is weak. However, the addition of salt to bring the chymosin out of the nettles is problematic as store-bought rennet isn't salty and the salt actually inhibits a lot of the bacterial culture action. (To try to work around this in my current project I've left the culture in the milk overnight at ambient temp).
So to my question!
All this makes me wonder: is there a better way to isolate chymosin from vegetables than plucking and boiling? Apparently it's in the sap of the nettles or mallow. Would it be possible to boil these vegetables and then distill the chymosin, rather than adding salt? Or is there a way of producing adequate sap from nettles or mallow just by juicing them? Has anyone else tried a project like this? I'd be fascinated in answers or suggestions as to how I might proceed. Fig sap rennet at the moment is out as the sap is strongest when the plant is fruiting in spring, summer and early autumn - but rennet from nettles or mallow is quite possible as they are plentiful.