Saturday, July 5, 2014

Effect of mash pH on flavor profile

Importance of mash pH

In a previous article on the mash, I mentioned that high pH can have adverse effects on the beer. Here is a write up of an experiment that tries to qualify the difference between two beers with different mash pH's.

What does a high pH do to my beer?

pH is a measure of the concentration of hydrogen ions in a solution. In explicit terms, the pH is -log[H+], where [H+] is the concentration of hydrogen ions in moles/L. A consequence of the -log function is that as the concentration of the hydrogen ion increases, the pH goes down. The most common range of pH is between 0-14, but it can be higher or lower and even a negative number (though a pH outside that range is very rare outside of a lab).

pH affects your beer in two ways. First, each enzyme in the mash has an optimal range of function in terms of temperature and pH. The enzymes responsible for converting the starches to sugars function most efficiently between a pH of 5.3 and 5.8. As the pH during the saccrification rest increases above 6.0, the enzymes will yield a wort that is less attenuative.

The pH also affects the flavor of the beer. The husks of the grain are full of tannins that can be extracted during the mash and sparge. The reaction pathway of how these chemicals dissolve into the beer is simple. The tannins are a weak acid and, like all acids, have a tendency to donate a hydrogen ion into solution. However being a weak acid, this donation only occurs when the concentration of hydrogen ions is relatively low (as is the case when the pH is too high).

If the concentration of hydrogen ions in solution is low enough, a hydrogen ion will dissociate from the tannin, leaving behind a negatively charged molecule. This negatively charged molecule can more easily dissolve into solution due to water's polar nature. This is why it is important to keep the pH in check: the free hydrogen ions will prevent the tannins from dissolving into the solution.

Most online sources give a pH threshold of 5.8 to 6.0 to prevent tannin extraction. This experiment was conducted to determine qualitatively where the tannin extraction starts in terms of pH.

Experimental Design

Two batches of beer were brewed identically except the water of one was not treated with phosphoric acid to reduce the pH. The two batches of beers are identified as B#160 and B#171. The mash pH of B#160 was 6.0, while the mash pH of B#171 was 5.8. Again, the aim of this experiment was to show how small changes in the mash pH can result in a completely different beer.

A survey was completed with nine participates to rate different aspects of the beer on a scale of 0-6, with 0 being not present and 6 being overpowering. The aspects are Aroma, Carbonation, Body, Hop Character, Fruity/Estery, Malty/Grainy, Roasted, Caramel, Aftertaste, Bitterness, Diacetyl, and Astringency. In addition to these specific categories, each participate rated their overall impression of the beer on a scale from -4 to +4; -4 is awful, 0 is average, and +4 is awesome. The ratings for each category were averaged and used to develop some sort of description of the beer.

Results
Table 1 - Batch parameters

There were some differences between the two beers other than the mash pH, which are tabulated in table 1. The "Final Runnings" is the last portion of the liquid that is run off from the lauter and into the boil kettle. The pH of this will be close to the mash pH at the beginning of the run off and will climb to neutral as the grain is sparged. The gravities are reported in degrees Plato. Ideally, the gravity of the final runnings should not drop below 3.0degP, and the pH should not be above 6.

The differences between the brews that led to interesting results in the surveys are the starting and final gravities. B#160 had a slightly higher starting gravity and a much higher final gravity. This is reflected in the lower % Attenuation, and can be interpreted as B#160 having more residual sugars. Both batches had accurate pitch rates, and were fermented with a low generation of yeast.

Survey Results

Table 2 - Survey Results
Table 2 shows the survey results in tabular form, while Figure 1 shows the results in a spider graph. The major differences are the overall rating and the astringency. B#160 had a significantly (with a 95% higher confidence) higher astringency and lower rating, while the other difference fell within the error of the experiment. B#171 was very well received by the taste panel who reported its astringency as barely recognizable.

The ratings for the caramel/roasted character are interesting if you consider the starting and final gravities of each batch. B#171 counter-intuitively rated higher in both caramel and roasted than B#160 in spire of a lower final gravity. This result might be attributed to the astringency of B#160 masking the caramel/roasted character of the beer.

Figure 1 - Spider graph of survey results
The other differences between the two batches were in the carbonation and the bitterness. The carbonation is reflected in the volumes of CO2 in the beer at the time of packaging. Bitterness is easily mistaken for astringency. This may explain why B#171 was rated as having less bitterness, in spite of having the same hop bill.

Conclusions and Take-away

This experiment shows that a 0.2 difference in the mash pH can lead to astringency that will be a detriment to a beer's flavor.

There are several options available to homebrewers for adjusting the mash pH. Using food grade phosphoric acid isn't an option, as it can only be purchased in gallons (enough for tens of thousands of gallons of beer). The most economical is to add 1-2% by weight acidified malt. This malt is coated in lactic acid, which will bring the pH of your mash down. However at high concentrations, the lactic acid can lead to off flavors. I've heard that many homebrew stores sell a buffer solution that you can add to your mash, but I have no experience with them.

This experiment highlights the importance of monitoring the pH of the mash to ensure it is in the range of 5.3 to 5.8. Litmus paper can be used to get an idea of the pH, but is no substitution for a digital meter. If you are serious about making good beer, a digital pH meter should be a priority investment. They are relatively cheap from amazon, and can cost less than a batch of beer.


NOTE:I am an amazon affiliate, and will only recommend products I have experience with. Below is the most reliable pH meter, as long as you take proper care of it.

No comments:

Post a Comment