madroaster Senior Member Joined: 30 Jul 2005 Posts: 111 Location: Canada Expertise: I love coffee
Espresso: S1V2 Grinder: CMH Drip: Hario V60 Roaster: In between roasters. SC/TO...
Posted Sat Feb 2, 2013, 5:40am Subject: Milk curdling in coffee
So I gave a family member a bag of Kenyan coffee from Heart roasters and no matter how it's brewed (temp wise, in an Aeropress), milk curdles when it hits the cup. Add the milk with the coffee cool? Curdles. Added hot? Curdles. Brewed at regular brewing temps? Curdles. Kick up the temp and brew at nearly boiling? Curdles. Different coffees brewed in the same way, using the same (fresh) milk and cream don't curdle. I've never seen this before and have no idea what's going on. Anyone?
Posted Sat Feb 2, 2013, 5:57am Subject: Re: Milk curdling in coffee
In order of likelihood:
1) The milk isn't fresh. Try better milk. 2) That wasn't good coffee. Stick with better coffee. 3) Question your family member's motives. 4) Why are you posting to the cheese lover's forum?
madroaster Senior Member Joined: 30 Jul 2005 Posts: 111 Location: Canada Expertise: I love coffee
Espresso: S1V2 Grinder: CMH Drip: Hario V60 Roaster: In between roasters. SC/TO...
Posted Sat Feb 2, 2013, 6:06am Subject: Re: Milk curdling in coffee
barkingburro Said:
In order of likelihood:
1) The milk isn't fresh. Try better milk. 2) That wasn't good coffee. Stick with better coffee. 3) Question your family member's motives. 4) Why are you posting to the cheese lover's forum?
1) Milk's fresh, and it was different milk at different times. Same milk doesn't curdle in other coffees. 2) The coffee's good; I've had it myself (hence the reason I bought it) and it doesn't have any noticable defects to speak of. It's insanely bright, but it's also Kenyan. I think the acidity obviously has something to do with it, but I wouldn't have expected acidic coffee to actually curdle milk. 3) Good point; maybe he's trying to mess with me. So far it's working. (More seriously, he knows very much what he's doing.) 4) I tried the cheese forum. They assured me that the curdling is all good.
Posted Sat Feb 2, 2013, 6:17am Subject: Re: Milk curdling in coffee
All kidding aside, I've had half n half curdle in my coffee... once. That time, it was a case of the dairy product not living up to its freshness date. The coffee never curdled half n half that was truly fresh.
Did you try the experiment yourself? Do you normally drink it black?
madroaster Senior Member Joined: 30 Jul 2005 Posts: 111 Location: Canada Expertise: I love coffee
Espresso: S1V2 Grinder: CMH Drip: Hario V60 Roaster: In between roasters. SC/TO...
Posted Sat Feb 2, 2013, 6:25am Subject: Re: Milk curdling in coffee
barkingburro Said:
All kidding aside, I've had half n half curdle in my coffee... once. That time, it was a case of the dairy product not living up to its freshness date. The coffee never curdled half n half that was truly fresh.
Did you try the experiment yourself? Do you normally drink it black?
I haven't got the coffee anymore, and it's no longer available so I can't try. I really wish I could though.
Apparently this morning's 10% cream was from a freshly opened carton. Since it also happened last week I'm not sure what to think of that. Seems like the milk is fine.
Posted Sat Feb 2, 2013, 7:33am Subject: Re: Milk curdling in coffee
I'm willing to bet that it's a combination of not quite fresh cream and very acidic coffee. When my half and half curdled, it was from a freshly opened container with a freshness date one week away. But I usually get half and half from a different store, and the freshness date tends to be a month away. I concluded that the store where I bought the product that curdled doesn't carry as fresh a product, and may even have storage problems. So every purchase from that same store could have the same problem. Using cream instead of milk or half n half will increase the chance of curdling, and hence place an even greater need on freshness. Using high acid coffee ups the stakes even more.
Usually a salt is used as a coagulant rather than an acid, but it can be done with acid. Lemon juice can actually be used. Coffee is not acidic enough to make true tofu, but it can make a mess.
Some brands of soy milk contain a stabilizer to reduce the likelihood of this happening.
Milk protein will denature at low pH. The only thing I can suggest (and I don't know if it will work) is to try real cream which has a lot less casein or some of those artificial whiteners.
Another possibility is that the coffee being brewed is overextracted, ramping up the undesired acidity in the final product.
I don't know that temperature has much to do with it, since milk and cream both can be pasteurized at much higher temps than your coffee is . . . but I am not a milk scientist :P
RoyceRuiz Senior Member Joined: 31 Mar 2012 Posts: 47 Location: Hollister, CA Expertise: I live coffee
Posted Mon Feb 4, 2013, 11:33am Subject: Re: Milk curdling in coffee
It is the the coffee. I once got a very bright and acidic Kenyan from Chromatic coffee (Very high quality, very fresh, about 3 days from roast). Every time my wife or I would add fresh half and half it would curdle. New cream, still curdled. Same cream, new coffee (a mild Argentina), no curdling. Sometimes coffee with high acidity curdles cream, especially if you use a high body brewing method (French press, Kone, Disk, etc.) but even with paper filters if the coffee is acidic enough.
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