First thing to say is that although “caprylic” flavour in beer is listed as an “attribute” in the ASBC/BCOJ/EBC/MBAA terminology system, it is probably better regarded as a “construct” (a combination of different attributes). The reason is that several different straight-chain fatty acids, including hexanoic acid, octanoic acid, decanoic acid and – to a lesser extent – dodecanoic acid contribute to the flavour (see Clapperton, 1978 and Clapperton & Brown, 1978).
Although octanoic acid (caprylic acid) is a key contributor to the caprylic construct, perception of the characteristic will be to some extent influenced by the concentrations of all four straight-chain fatty acids in the beer to which it is added.
Concerning the nature of the construct, it is primarily a mouthfeel. Typically described as “fatty” or “soapy”, but recognized as contributing to perceived “body” too. This is mainly due to retronasal flavour; but some direct impact on other senses (taste and mouthfeel) are likely. From my own perspective, I reference the flavour to Chardonnay wine (which is subject to frequent rousing of yeast – so-called “sur lie ageing”) as well as to the mouthfeel of coconut water.
At higher concentrations, a retronasal odour can be perceived. This resembles candle wax. Such odours are found at levels of straight-chain fatty acid which are not typical of commercial beers. Samples which display this note include beer recovered from yeast, and tank bottoms.
Factors affecting the flavour impact of octanoic acid in beer
Factors affecting the flavour impact of octanoic acid in beer
A number of factors affect the flavour impact of octanoic acid in beer. These include:
- Concentration of octanoic acid in beer
- Concentration of other straight-chain fatty acids in beer
- pH value of the beer
- Mineral concentrations in the beer – particularly calcium and magnesium
- Protein content and composition in the beer
- Ethanol content of the beer
In addition to these beer-specific influences, the flavour impact of octanoic acid in beer is also influenced by the method of addition (in cases in which it is added to beer post-production, such as occurs in preparing samples for tasting).
Addition of octanoic acid in the form of a stock solution in ethanol, propylene glycol or alkaline water leads to some unusual behaviour in the beer subsequent to the addition. For example, Roberts & Clapperton (1978), showed that addition of an octanoic acid stock solution to beer just before tasting resulted in the most intense flavour, while adding the compound to beer at the time of bottling resulted in a less intense flavour.
To quote from this paper: “This work shows that care must be taken when adding fatty acids or other lipid-like materials to beers to determine their effect on flavour. For the added compound to have an effect similar to that of the compound naturally present in the beer it should be added well before tasting, and if necessary shaken in the beer to ensure dispersion. It is only by trial and error that the time for full dispersion can be judged. However, if this procedure is not adhered to, an erroneously low value may be obtained for the flavour threshold concentration of the substance in beer.”
More than 40 years on from this paper, we have a better understanding of what happens when solutions of fatty acids are added in beer. As the stock solution is mixed with the beer, precipitation of some of the fatty acid occurs. This leads to formation of microdroplets and (invisible) nanodroplets. Essentially, we form an emulsion rather than a true solution. These droplets have very different physical behaviour in comparison with the free fatty acid dissolved in the beer. The “droplets” are more likely to accumulate at surfaces, and may therefore be easier to detect by odour. They may also impact mouthfeel differently than free molecules in solution. Over time, the molecules in the droplets will dissolve in the beer. But even those dissolved molecules will not all be available to contribute to beer flavour. For example, at a beer pH value of 4.7 – 50% of the molecules will be in a charged form, and therefore odourless. Over time, some of the dissolved molecules will form insoluble soaps with calcium and magnesium ions (with the effect most pronounced in highly mineralized beers). And some of the fatty acid molecules will be adsorbed onto lipid-binding sites in proteins (such as the lipid-binding protein LTPT1 from malted barley and wheat). The overall effect will be a change in flavour impact of the added fatty acid, with less orthonasal smell (less volatility) and relatively more retronasal flavour and mouthfeel.
But what about fatty acids added to beer using molecularly-encapsulated flavour standards? This is where practicality and science collide. When a flavour standard is added to beer, the octanoic acid molecules are released one by one from cyclodextrin molecules which are physically separated within the liquid. They thus dissolve instantly, avoiding the precipitation and coalescence of droplets which occurs when the fatty acid is added as a solution in ethanol or another liquid solvent. We can expect that over time some of these fatty acid molecules could be lost from the beer through binding to proteins, formation of soaps with calcium and magnesium, absorption to packaging materials and the like. But, by design, the flavour standards are added just before training assessors, so this shouldn’t happen.
Summary
As you’ll see from the above, “caprylic” is no ordinary beer flavour; and octanoic acid is no ordinary flavour molecule.
I’ve focussed on the beer and the flavour standard, but we also have to consider the assessor. The perception of fatty acids is very important in human behaviour (through perception of “signals” from other humans and other animals). In consequence there can be striking differences in sensitivity from one person to another with respect to different fatty acids.
On top of that, diet and health also play a part in determining whether or not and individual assessor will perceive such characteristics.
