Hop Champ Episode 6: Water Chemistry Is Bitterness In this episode we break down the exact mechanisms the cause mineral ions like Calcium, Magnesium, and particularly Calcium Sulfate to be tasted as bitter. To be clear, we are NOT talking about these ions "bringing out hop bitterness", we are clearly demonstrating that these mineral ions are themselves bitter.Subscribe to the Hop Champ Channel on Substack to access the Hop Champ IPA tasting app for Google Sheets. Click Here to Subscribe, Read More Research Notes, or Reach Out The Notes That Built Ep 6 Are Below: One. Do minerals added to the water chemistry of beer taste bitter themselves? Yes. We need to be very clear and upfront about this; the calcium, magnesium, chloride, and sulfate that are added to any beer contributes to the total bitterness tasted in that beer through a very specific and well defined mechanism. There are many different cell types in the human palate that calcium and magnesium interact with to produce a wide variety of effect on the flavor and mouthfeel of a beer…and one of the cell types these minerals interact with is a taste receptor cell which only detects minerals and only sending sends bitter taste signals to the brain. When two complex systems interact the way that they do when we taste a beer (the beer is one complex system and you the most complex system we know about), linear effects don’t exist, just general trends and increased probabilities. When we add calcium sulfate, for example, to beer, that addition does many things and one of those things is to contribute a significant increase in bitterness to the beer, but not every molecule of calcium sulfate contributes to this bitterness, just a higher amount than calcium that isn’t bonded to sulfate. Two. Why do we taste these minerals, and the ionic compounds that contain them, as bitter? In previous episodes of this podcast, particularly episodes four and five, we discussed some of the specialized taste perception cells on the human palate. These receptor cells are the very first stage of how we perceive taste. Generally speaking, taste begins with these receptor cells, and we have many types of them, and when those receptor cells are activated they send signals through nerve pathways, like the trigeminal nerve and the vagus nerve, to brain structures that process those signals, typically a group a neurons called the Gustatory Cortex processes the signals first before sending them to very specific places in brain structures like the Amygdala and the Hypothalamus. We taste bitterness through a specific group of receptor cells called the TAS2R group of taste receptor cells. There are 26 varieties of these bitter taste perception cells that we know about right now, with the 26th one only recently being identified by researchers. Some of these bitter receptor cells can interact with a wide variety of bitter compounds and we see this broad interaction with many of the bitter components in hops. In the case of the water chemistry components that we’re talking about today like magnesium chloride, magnesium sulfate, calcium chloride, and calcium sulfate, which are considered ionic compounds so that’s how we’ll refer to them, we have a well documented account of a very specialized TAS2R receptor named TAS2R7 that is very precisely tuned to respond to these ionic compounds like magnesium and calcium, along with other compounds that are much less abundant in beer so we don’t have to worry about them in this discussion. TAS2R7 is a G protein-coupled taste receptor.. Like all of G Protein-Coupled receptors, the molecules that it is specifically calibrated to respond to interact with specific amino acid residues on the receptor cell and that triggers a breakdown of the G protein into subunits, and those subunits initiate the complex signaling pathway to the brain letting it know that we’re tasting something bitter. So, what causes the TAS2R7 receptor to send a signal that we’re tasting something bitter when it interacts with one of the minerals that we’re examining today? A few definitions will be useful as we explore this: Ionic Compound: is a molecule made from two or more molecules whose charges balance each other out and make the total charge of the ionic compound neutral. Ionic compounds are made up of cations and anions which are balanced to achieve this neutral charge. cation is a positively charged ion. Calcium and Magnesium. anion is a negatively charged ion Sulfate and Chloride. An Ionic Compound is made up of Cations and Anions * TAS2R7 is activated by divalent and trivalent cations, including zinc, calcium, magnesium, copper, manganese, and aluminum. Divalent and Trivalent simply refer to the specific charge of the ion. Divalent has a charge of +2, and Trivalent has a charge of +3, and these charges play a key role in how ionic compounds we’re examining are able to interact with the TAS2R7 receptor cell. These positive charges don’t just have to be positive, they have to be strong enough; Potassium, with a charge of +1, won’t interact with TAS2R7 because its charge does not cross the required energy threshold. * Molecular Interactions: Molecular modeling suggests that the negatively charged residues in the TAS2R7, specifically H94 (histidine at position 94) and E264 (glutamate at position 264) are key to the receptor's interaction with metal ions. * These residues are thought to interact with the metal ions through strong electrostatic interactions, meaning the interaction between positive and negative charges. Three. What Does Our Research Cluster Say About The Effect Magnesium Has On Bitterness? We can start with magnesium, because it’s the very straightforward example of mineral bitterness. Our research cluster shows that magnesium sulfate and magnesium chloride interact with the TAS2R7 taste receptor very significantly and cause the receptor cell to send a signal of bitter taste perception to our brain. With magnesium sulfate and magnesium chloride; the magnesium causes the response of the taste receptor cell and the anion that is paired with it, the sulfate or chloride, changes how much magnesium is required to cause a particular level of activation of the receptor cell, these studies measured two typical activation levels of the receptor cells, fifty percent activation and the maximum possible activation. The presence of sulfate increased the amount of magnesium needed to activate the TAS2R7 receptor cell compared to chloride ions. Which is interesting and something we’ll dig a little deeper into when we’re discussing calcium. So the takeaways from the research on magnesium is; anytime we’re adding magnesium to a water profile we’re increasing the bitterness of the beer. And the chloride and sulfate ions change the bitter perception of that magnesium. Obviously, when we’re talking about beer and not isolated lab experiments we’re talking about a liquid that contains a blend of chloride and sulfate ions which will result in a unique modification of magnesium’s ability to activate the TAS2R7 receptor cell. Four. How does Calcium, in the form of Calcium Chloride, Calcium Sulfate, and ionic Calcium increase bitterness in beer? Calcium has a more complex interaction with TAS2R7 taste receptor cells than what was observed when magnesium was tested. In our research cluster a laboratory that was studying the way minerals interact with the TAS2R7 receptor explored the interaction of calcium with the receptor cell and were able to say that the presence of calcium increases the overall activity of this receptor cell in response to any other compound that it detects. They were able to logically infer that calcium itself is activating this receptor cell. They had to make this an inference, a logical hypothesis based on what they measured but not an official result, because the experiment didn’t test ionic calcium, or calcium not paired with sulfate or chloride, by itself, just ionic compounds paired with chlorides or sulfates. The research tested the ionic compound calcium chloride, which is very useful to us, and the researchers also used a solution containing un-paired, “ionic” calcium ions to dissolve all the compounds it was testing. So, this examination of calcium chloride took place in a solution that had calcium ions added to it before any of the tested compounds were dissolved into it, which we’ll call Free Calcium in this discussion because it was not added as an ionic compound, was the relationship that the led the researchers to make the logical hypothesis that calcium itself activates the TAS2R7. All of these minerals were tested by dissolving them into a solution and adding them to a receptor cell that had been isolated by the laboratory. It’s important to note that ionic compounds dissociate when added to water. Full Dissociation means that when calcium chloride is added to water the ionic compound, the bond between the calcium cation and chloride anions breaks and the calcium and the chloride are dissolved into the water as individual ions. That means that when these experimenters are examining the effects of calcium chloride, they are essentially examining the effect of free calcium ions on the TAS2R7 taste receptor in the presence of Free chloride ions. This is important because it lends an additional layer of credibility to these researchers presenting the opinion that calcium itself is capable of activating the TAS2R7 receptor cell even though they did not include a direct experimental interaction of calcium and the receptor cell in their experiment. As for the test of Calcium chloride itself, calcium chloride doesn’t have the reputation for bitterness that calcium sulfate has in the brewhouse but was documented in this laboratory research as activating this bitter taste perception cell. This finding actually aligns with numerous studies that examined the effect of these compounds on the taste of water usin
