Level: Apprentice
Read Time: 8 minutes
“A year ago I took a chocolate tasting class from the IICCT. During a tasting in the class, the instructor said that he tasted a little rancid cocoa butter in one of the samples. He said that it is something that many of the tasters are starting to notice during some tastings. So, if rancid cocoa butter is an issue, what temperature are we supposed to be storing it at?”
This kind of thing tires me out. For me this is the height of posturing and ignorance and it pushes my buttons. It comes across as snooty (or snotty, maybe both) attitude.
“dude, take a chill pill” I can hear some of you saying. Ok. Breathing. Chilling. Finding my center Zen.
<Finding my inner Mr. Rogers>
<soothing, low, rumbling mellow voice>
Hi everyone, let’s talk all about rancidity today. We will explore how I stopped worrying about rancidity and learned to love the solidity.
The TLDR version off all of this is that the fats in cocoa are of the wrong type to go rancid so if someone is tasting something they think is “a little rancid” they have to be mistaken. Possibly they taste something they don’t like but it is hubris to think they know the cause.
Rancidity occurs when oils are exposed to heat, light and/or oxygen over time. The fat breaks down into smaller particles called fatty acids.
There are five types of rancidity: oxidative, hydrolytic, enzymatic, photo-oxidative, and microbial.
Oxidative: Oxygen reacts with unsaturated fatty acids which in turn form various aldehydes and ketones. These molecules are responsible for the unpleasant and very distinctive odor and flavor of rancid foods.
Hydrolytic: Water reacts with triaclyglycerides (lipids/fats/oils) which leads to the formation of free fatty acids and glycerol. Free fatty acids can then oxidatively react forming aldehydes and ketones.
Enzymatic: As the name suggests, this is caused by enzymes which lead to the formation of free fatty acids and glycerol, et all. Yep, more aldehydes and ketones.
Photooxidative: light breaks apart bonds in oils that lead to the formation of free radicals which can then further react to form, you guessed it, free fatty acids, aldehydes and ketones.
Microbial: Caused by certain bacteria. You know what they form.
Chocolate is by definition a waterless environment. That right there allows us to eliminate Hydrolyic and Microbial rancidity. In theory, because they contain water, the raw cocoa beans might be able to go rancid but in practice because the cocoa butter is all bound up in the cells and isolated from oxygen and bacteria that doesn’t happen.
Enzymatic is out as enzymes are proteins and are fully removed during the extraction process when making cocoa butter. Sure, they could be in the cocoa bean but before roasting they are isolated and post roasting there is no water.
That leaves us with oxidative and its variant photo-oxidative.
In both cases unsaturated fatty acids have to be involved. What you ask are unsaturated fatty acids? Have a gander at this.
Did you spot the difference? It is those extra horizontal lines that denote double bonds. Those are a little extra chemically reactive and that little bit of instability is required for rancidity to occur. Does cocoa butter have some of those? As a matter of fact it does.
It is the most abundant fatty acid there is Oleic acid and is unsaturated. But it isn’t that easy. The answer is more nuanced than that. Notice how all those fatty acids up there are hanging out all by themselves? That isn’t how cocoa butter is. It is instead formed by three of those free fatty acids called a triglyceride and that changes so many things.
Sure, an unsaturated fatty acid is in there but it is surrounded by twice as much saturated fatty acid and that goes a long way to protecting that double bond and that in turn keeps it from going rancid. It is sort of like a splint surrounding an unstable knee. But it goes beyond that and as it turns out that knee analogy is pretty apt. It keeps everything more solid and in regards to fats, that means that it is a solid at room temperature.
The whole thing about rancidity is that it can self propagate. I’m not going to jump into all the nitty gritty chemistry of that as it isn’t all that important except for knowing that you need motion for the rancidity to spread.
Picture three glasses of water. One is frozen, one is at room temperature and one is boiling. You place a few drops of red dye in each. Which one is going to turn completely red first? It is going to be the boiling one as the solution is self stirring, swirling and roiling. The room temperature one is next and if you keep it frozen, the ice is not going to spread any color at all.
Chocolate is solid. Cocoa butter is solid. They are ice. Nothing is going to happen.
Remember what I said at the beginning?
“Rancidity occurs when oils are exposed to heat, light and/or oxygen over time. The fat breaks down into smaller particles called fatty acids. “
Yes we melt cocoa butter but it takes a LOT to oxidize cocoa butter. Check out the heat and time it took just to study it.
“To evaluate the oxidative behavior of cocoa butter, the autoxidation of refined and non-refined butter samples was accelerated (oxidized at day light at room temperature and at 90 °C). The quantity of certain aldehydes formed during the oxidation of cocoa butter was examined by gas chromatography. The oxidation stability of butter was evaluated over a 12-week period. “
The accelerated version was 12 weeks long. It was heated to a brutal 90 C. And it was exposed to light continuously. So sure, it will in fact oxidize and go rancid....but not at any temperature we are going to be exposing it to. A brace stabilized wonky knee will also get worse if you run a marathon a day for 12 weeks.
Keep in mind, you don’t just have to oxidize that one double bond. You need to break apart that triglyceride into free fatty acids first. Only then can you start the actual rancidity cascade and even that is difficult. I dove into the actual study and the short take away of what I observed was that it took 3 weeks with continuous light and some combination of high temperatures and/or metal accelerators like iron and copper before any real above baseline oxidation was shown.
And one more thing just to round out your knowledge of rancidity.
Peanut oil is often touted as one of the best oils to subject to heat. Why? The high levels of oleic acid and the absence of linolenic acid account for long fry life. The same oleic acid is in cocoa butter. So even though it technically meets the requirement of being an unsaturated fatty acid, it just isn’t prone to going rancid.
All this in totality is why I call BS on anyone saying they notice rancidity in chocolate and why you really just don’t have to worry about it. Oh right, the actual question.
“So, if rancid cocoa butter is an issue, what temperature are we supposed to be storing it at?”
You got this, right?
Cool, dry and dark.
Pretty much the same answer I give to storing most everything chocolate related.
Now you know why.