Effects of mash parameters on fermentability and efficiency in single infusion mashing
It is commonly known that there are many factors that affect the fermentability (limit of attenuation) of brewing wort. The series of experiments conducted here are aimed at understanding not only the qualitative impact but also quantify the changes of fermentability depending on the parameters that were considered for evaluation.
In Understanding Attenuation it is mentioned that final attenuation of a beer mainly depends on 2 factors: limit of attenuation and the yeast's ability to come close to that limit of attenuation. The limit of attenuation is only affected by mashing and the Fast Ferment Test has been introduced to determine it. For simplicity sake, these experiments only focus on single infusion mashes and explore the affects of the following mash parameters:
- saccrification rest temperature: This is the first factor that comes to mind for all grain brewers. For a single step saccrification rest, the mash temperature has a great affect on the fermentability of the resulting wort. The lower the temperature (within a given range of course) the longer the beta-amylase will be able to work and produce maltose. See The Theory of Mashing.
- water to grist ratio: the enzymatic activity of the amylases is affected by the thickness of the mash. Thinner mashes enhance the maltose production and therefore increase the fermentability. See The Theory of Mashing.
- grain bill composition (base malt): mashes with high diastatic power (Pilsner, Pale) will produce more fermentable worts since they contain a lager amount of beta-amylase which can produce more maltose than mashes with lower diastatic power (Munich or large amounts of unmalted grains) assuming the same saccrification rest temperature.
- mash pH: the beta and alpha amylase enzymes have different optimal pH ranges (beta amylase : 5.0 - 5.5 pH; alpha amylase : 5.3 - 5.8 [Palmer 2006]) and therefore the mash pH can affect the activity balance between these enzymes. Though the effect is only marginal. See The Theory of Mashing.
- grind: larger grits of endosperm make it harder for the mash water to fully hydrate them and make the starches accessible to the enzymes. The as a result lots of starch is released later when the beta amylase activity is already diminished. The result of a coarser grind is a lower limit of attenuation. See The Theory of Mashing.
Contents
Materials and Methods
All experiments were conducted at a relatively small scale with minimal overhead. The strike water was heated in the micro wave. The time spent in the micro wave was noted for each experiment and provided a guidance for future experiments. After a number of experiments it was possible to come close to a desired mash temp by estimating the necessary heating time. The water was then added to a small steel thermos bottle where it was left for about 5 min to settle. A Styrofoam stopper was fitted for the bottle which also held an alcohol filled thermoter. The tip of the thermometer reached into the water/mash and it was possible to read its temperature without opening the bottle. The settled temperature was recorded and the milled grain was sirred into the water. 5 min into the mash the mash temperature was recorded. It was also recorded 30 min into the mash. Then the mash was stirred and its temperature recorded 5 min later. The last time the temperature was recorded was at the end of the mash.
Once the 60 min mash was complete a sample of the wort was tested for starch conversion with iodine on chalk. This was only done for select mashes. The mash was then lautered through a stainer set over a pot. In all cases it took less than 2 min to bring the first runnings to a boil. In the meantime sparge water was heated in the microwave and the grain was well mixed with the water before it was lautered again through the strainer. This sparging technique resembled a batch sparge.
After the wort was boiled for 15 min it was strained though a paper towel set in a funnel. The funnel was placed into a clean 12 oz bottle. Initial experiments sanitzed the bottles and the funnel in boiling water. But that became to cumbersome and due to the high pitching rate that was to follow the affect that infections could have on the attenuation measurement was deemed insignificant. The wort in the bottle was then topped of with reverse osmosis water when necessary. Initial experiments didn't care about the precise amount of wort in the bottle unless there would be enough for 2 hydrometer readings, but later it was decided to keep the volume the same (top off when necessary) to get a measure of the mash efficiency along with the attenuation.
After capping the bottle with aluminum foil, the wort was left to cool at room temperature. Once cooled the original extract was measured with a hydometer (range 0 - 40 Plato) and then pitched with 1/2 teaspoon of Fleishmann instant bread yeast. Dry bread yeast was chosen for its low cost. In previous fast ferment tests, where it fermented along side other yeasts, it has been determined that it attenuates similar to other ale yeasts.
The samples were fermented at about 20 C (70 F) for 4-6 days. They were occasionally shaken to rouse the yeast. After the 4-6 days of fermentation the yeast started to settle and no visible signs of fermentation were left. The final extract (=final gravity) of the sample was measured with another hydrometer (range 0.990 - 1.020). Both hydrometers were calibrated with various sugar solutions (20, 10, 5, 2.5 and 0 Plato) and the readings were also corrected for temperature.
Temperature experiments
For the temperature experiments, the following parameters were kept constant:
- grain type: Weyermann Bohemian Pilsner Malt
- grain weight: 80g
- mill gap spacing: 0.55 mm
- reverse osmosis water and no pH adjustment of the mash. The resulting mash pH was measured as 5.4
- strike water volume: 240 ml
- sparge water volume: 250 ml
- mash time: 60 min
- boil time: 15 min
pH experiments
For the pH series experiments, the following parameters were kept constant:
- grain type: Weyermann Bohemian Pilsner Malt
- grain weight: 70g
- mill gap spacing: 0.55 mm
- reverse osmosis water
- strike water volume: 240 ml
- starting mash temperature: 73 - 74.2 C
- sparge water volume: 250 ml
- mash time: 60 min
- boil time: 15 min
- final wort volume: 15 min
The mash pH was ajusted with either vinegar (5% acetic acid) or baking soda (5% w/w NaHCO3 solution) which was added by volume with a small syringe.
The pH of the samples was measured at the end of the mash. Because the probe of the pH meter is getting old and its calibration function wasn't working anymore, the correction of the measured value was done externally by measuring the sample, a 4.01 reference buffer and a 7.01 reference buffer. The following equation was used to determine the actual pH of the sample:
corrected pH = 4 + 3 * ((sample pH - 4.01 buffer pH) / (7.01 buffer pH - 4.01 buffer pH))
In addition to that, the samples were also tested with EMD's colorpHast strips, which were read against the color scale in tungsten light. Reading them in fluorescent light actually changes their color. All samples were cooled to room temperature before measuring their pH.
Results and Discussion
Temperature
The first series of experiments was conducted with a variation of the mash temperature. Unfortunately the small mashing vessel, that was used (stainless steel thermos bottle) caused significant mash temperature loss, as well as the stirring at 30 min. This needs to be taken into account when interpreting the temperatures shown in Figures 2 and 3. The approximate mash profiles for all the sample mashes that were done are shown in Figure 1. Dough-in happened at time 0 and the mash was quickly lautered after 60 min. The wort pH was measured at 5.5 (at room temperature)
Figure 2 shows the limit of attenuation numbers that were measured for the various mash experiments in this series. Two things were surprising. First, all data points track along a curve very nicely. There is also not much difference between points at similar temperatures. This is a validation for the repeatability and low statistical error of this experiment. Second, the peak of attenuation seems at much higher temperatures as one would expect from practical mashing with single infusion mashes. This is considered a result of the larger temperature drop that was observed during the laboratory scale mashing. Because of that the temperatures listed here should NOT be used to predict the single infusion mash temperature necessary for a brewers mashing system. The only conclusions that can be drawn are what should be expected when that rest is held at lower or higher temperatures.
Another remarkable observation is the almost perfectly linear shape of the attenuation slope after its peak. The linear function that has been fitted to match the data points has a slope of ~ 4 %/C. This means that increasing the temperature by one degree Celsius (1.8 F) will lower the limit of attenuation by 4%. This was found to be true over a fairly wide temperature range (12 C / 24 F). However, the slope leading up to this peak is not as steep. This is assumed to be a result of stronger beta amylase activity which causes the production of maltose as soon as starch gelatenizes and alpha amylase is breaking down the amylose and amylopectin molecules into shorter dextrines.
In addition to the attenuation, an iodine test on chalk was performed at the end of the mash and the beginning of the boil. The results can be seen at the top of Figure 2. Note the mahogany color, witch is an indication of existing dextrines. This was expected to be seen for samples with a low limit of attenuation, but even sample number 10, which achieved 87%, shows a significant mahogany iodine reaction. More iodine tests for samples past the attenuation peak need to be added to confirm a trend. Surprisingly little of the iodine reaction carried over into the boil even though care was taken to heat to wort quickly to minimize the time spend in a temperature range that favors the alpha amylase activity (68 - 78 C/ 155 - 172 F). Note that this is not realistic in the brewing practice where even without performing a mash-out, the collected wort spends some time in this range while it is heated to boiling.
Later experiments (number 12 and up) were also done in a way that allows for a comparison of the brewhouse yield. For these experiments the post boil wort volume was also recorded. Because the lauter efficiency can be assumed to be the same for all experiments (all mashes were lautered batch sparge style with 1 sparge), the differences in brewhouse yield (also known as brewhouse efficiency) must be largely due to changes in the mash efficiency (a measure of how well the mash converted the starches). From the few data points that exist so far it is evident that lower temperature mash rests lead to a lower mash efficiency. Which is expected since not as many starches have gelatenized yet and the alpha amylase, which is the major enzyme responsible for liquefying starches, is less active. Note that all experiments were done as 60 min mashes and that the lower efficiency at the lower mash temps can be accounted for by mashing for a longer time.
Figure 3 shows another twist on representing the attenuation data. For this chart, all the brewed worts were assumed to have an extract content of 12 Plato (equivalent to 1.048 SG). Instead of showing the limit of attenuation, the attenuation was used to calculate the lower limit of the final extract (=gravity) of the beer. This is the extract reading you would expect to get from a fast ferment test or a very well attenuating yeast which left the beer with very little or no fermentable extract.
pH
pH meter vs. colorpHast strips
Table-1 lists the pH corrections that were done and which pH was measured with the pH meter and the colorpHast strips. The first column lists the experiment number and the second column the amount of acid or baking soda solution that was added. It is interesting to see that the pH meter measurements for experiments 19 and 23, which both received no pH treatment, are fairly close while the strips must have been interpreted differently between the 2 experiments. Another remarkable observation are experiments 24, 25 and 26, which received different amounts of acid, caused different pH meter readings, but all read 4.7 on the color scale for the pH strips. This affect was also observed when I tested the pH meter against the strips a few months back. The results of that test are published here
