“Um, excuse me sir. I think this half and half is bad. It is curdling in my coffee.”
Bad half and half or dairy is a logical deduction. I once thought this was the only reason too. Therefore, I would throw out every ounce of what I perceived to be bad creamer if it even hinted at curdling. It didn’t matter if the expiration date was several days away. However, after tiring of throwing out good milk or half and half I learned there are other factors that can cause your creamer to curdle in your coffee.
We are very particular with our creamer we serve here in shop. Half and half shelf life when opened and put in our container is about a week or more. We never leave our creamer out longer than a few minutes often pulling it in and out of the refrigerator for each customer. We do this because we want our creamer to stay cold and fresh longer. Also we get an order of creamer about once a week to every other week. Unopened creamer in the fridge can last a month or more depending on the coldness of the fridge. We change out our creamer every two days, 3 times a week, regardless of what is left in it. This means that we run through 6 cartons of cream in two weeks, well before the expiration date. I do not like seeing curdled dairy in anyone’s coffee. I cringe! But, alas, I can cannot control all factors. Temperature and acidity are two of those factors.
We serve our coffee hot, usually between 195 – 200 degrees. The fridge temp ranges between 32 and 42 degrees as it cycles through the day. The very hot coffee coming in contact with the very cold creamer starts the initial chemical reaction. Have you ever seen what happens when you mix lemon juice with fresh milk or half and half? It curdles quite quickly. Both coffee and milk are acidic, milk becoming more acidic as it ages because the existing lactic acid increases. Our caramel syrup is a perfect example. We wondered why our steamed milk does not pour as well in caramel lattes as it does with our other syrups. We discovered that one of the ingredients in that particular syrup was lemon juice. That doesn’t necessarily mean the cream is not fresh. The lemon juice acidity of the syrup is the greater culprit here. And it is so with certain coffees. Some coffees are higher in acidity than others because they are farmed at a higher elevation which generally produces a higher acidity. African coffees often fall into a higher acidity category than other coffees because of this reason.
Roasting can also effect acidity. It cannot intensify acidity, but it can diminish it depending upon the length of time it was roasted. Our local roaster primarily roasts coffee to a medium level. Companies that roast a little darker will diminish some of the acidity out of batch of coffee. Many people drink dark roasts and add milk. If it curdles there is a good possibility the dairy is not good. It isn’t so clear cut with medium to light roasts.
In summary, if dairy creamer is properly stored and monitored it could be reasonable the really hot or acidic coffee actually changed the pH of the milk making it curdle. Next time your milk slightly curdles you are now more informed on what it might be. Do not hesitate to ask if the half and half is any good. A coffee company should never tire in answering that question. But now you know that it may not be bad creamer. Instead you may have just witnessed a chemical reaction in your creamer’s pH due to acidity and length of roast.