Let’s start with the coffee and figure out how the coffee itself could be different day to day. We already know that coffee stales just a little bit everyday and that if it is already ground, the process happens at a much faster rate. But is it really that fast a process?

Probably not, at least, not so fast that we can tell after just one day.

What we always assume, though, is that the bag or can of coffee is perfectly homogenous, that is, every bean inside is nearly identical. The truth is, that rarely happens.

Sometimes, bad beans make it into the lot. These beans are usually bad from the start—they were picked that way or they processed poorly and were mixed in with good coffee.

While there are many ways of sorting out bad beans (hand picking, screening by size, separating by density, and color sorting) none of them are perfect. Bad beans will always sneak through the system.

Did you know?

A pound (455 g) of medium roasted coffee will be composed of 2,800–4,725 coffee beans (depending on their density).

Sometimes, you can see these beans in a bag of whole bean coffee. They often are discolored (usually lighter) but really junk ones can be all black. Some are broken or have evident insect damage. These beans are more difficult to see and taste in darker roasted coffees, but some can still leave their mark on the cup. Every so often, though, beans that make it past all the sorting and look just fine in the roasted bag still end up tasting a bit off from the rest.

Generally, there aren’t very many of these beans. So, the odds of one getting into any given pot are low. Even if it did make it into a pot, if it were just one bean, it would probably be so diluted as to be unrecognizable. As an extension, a bag of ground beans are likely to be much more homogenous as they’ll be able to mix much better. If you are brewing just one cup at a time, though (an increasingly common practice), a single bean can make an incredibly big difference. So, it might just be the case that one bad bean spoils the whole cup, making today’s cup different than yesterday’s.

Hopefully, though, that doesn’t happen too often, which suggests that differences in how our coffee tastes day to day are due to something in our heads. We are thinking, feeling creatures who use our brains to process everything. Whether it is a translation of the electrical signal received after a sugar molecule interacts with a taste bud or the frustration from the cat leaving a carcass in the hallway, or our brain interpreting the gestalt of the experience of an incredible cup of coffee, it is all dependent upon our psychology and how our brains work. So, we’re not actually crazy; we’re just human. And this means all kinds of explanations exist to explain this inconsistent coffee phenomenon! 

Did you know?

To produce 1 pound (455 g) of roasted coffee, at least 6.5 pounds (3 kg) of coffee cherry must be picked.

One explanation to explore is that we rely too much on our sense of perfection while measuring things. Specifically, we aren’t all so good at measuring weight, volume, and temperature. Moreover, many household measuring tools (measuring cups and spoons, specifically) aren’t as precise as we may need them to be and let’s not even start about the measured lines printed into coffee pots. It is quite likely that in our overconfidence, we measure the water, the coffee, or the water temperature differently day to day. This would certainly produce cups that taste differently enough to recognize. Fortunately, the solution is pretty simple: weigh everything. We talked about brew ratios in a previous section. If you weigh the coffee and the water, your level of consistency will skyrocket (FYI, 1 milliliter of water weighs 1 gram. Thus, you can exchange volume for weight if you’re measuring using the metric system). If you heat your own water, use a thermometer.

There’s no reason to guess and have variable tasting coffee when cheap, simple tools will solve the problem. 

Let’s be honest, mismeasuring water isn’t something we really want to blame on us being human. It is really more about being lazy and ill-equipped than anything else. The truth is, we are subject to the whims of our psychology in very real ways.

It might just be that we have bad memories. I don’t mean that we just don’t quite remember what we tasted last time but that we actually have really terrible memories.

Even though we feel confident that we remember specific details about things, we often get them wrong. More frighteningly, it is easy to create memories in people of things they have never experienced. To top it off, every time we remember things that are actual memories, we change them ever so slightly. It may not be that the coffee is different at all, rather, you’re just remembering it differently!

Aside from having lousy memories, our ability to taste is heavily influenced by so many external factors. We should all be wary of how we interpret our eating experiences because of how susceptible we are to the world around us. For example, the color of ambient light influences how much we like a wine and how much we’d be willing to pay for it (blue and red lights produced higher ratings than white and green lights). We’re also influenced by the color of the dish or cup, the colors of food on the dish, and the colors around us.

Ambient sounds are incredibly influential on perceptions of foods, including the sound of the food itself (e.g., the crunch of a potato chip or the sizzle of carbonated water), the sound of the packaging, the sound of machines, the sound of music, and the sound of the sea. To name a couple specific to us, coffee aroma is rated higher when the drinker can hear someone else who is drinking coffee rather than someone eating a potato chip. The quality of the sound of the coffee machine influences how much we enjoy the coffee as well (bad sounding machines cause us to like the coffee less).

Our sense of touch can make us think differently about how things taste. The texture of packaging changes our mind about food as does the weight of the dish. Even the material a spoon is coated with will make us rate the food somewhat differently. Research combining a variety of environmental cues on the perception of whiskey demonstrates that our mind doesn’t focus on just one influence at a time, but is bombarded by them all!

Not only do environmental cues trick us into thinking differently about how we taste, but so does our emotional state. Being in love, in a positive or negative mood, or depressed will make you think differently about what’s happening in your mouth. It is likely that other emotions can influence our organoleptic responses.

It is evident that we are lousy instruments. Although we may not be conscious of it, many little, seemingly insignificant things actually have a significant impact on how we experience foods and beverages. Considering this, it is no surprise at all that coffee can taste differently from one day to the next. It may not be the coffee that’s different; it may be you!

Did you know?

The first commercial espresso machine was produced in 1905 by Desiderio Pavoni. 

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