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Avoid energy losses
It is common practice to recover hot water for the mashing and sparging process during wort cooling. However, low mashing-in temperatures can lead to an excess of hot water, as less hot water is used for the main pour. If the hot water tank overflows, energy is lost unnecessarily.
TIP: The mash can be heated up by adding hot water to the mash. The amount of hot water can be calculated using equation 1.
Equation 1Calculation of the needed volume of warm water for scalding with:
• m = mass
• T1 = temperature of the mash before hot water is added
• T2 = Temperature of the hot water
• T3 = Temperature of the total mash after hot water has been added
Low temperatures during mashing-in can lead to excess hot waterEvaporation losses must be avoided, especially in decoction processes, as it is usually not economical to install a pan vapor condenser in mash tuns. Heating the boiling mash to a maximum of 95 °C is sufficient for the physical decomposition of the mash particles and also prevents evaporation losses. Then there is no difference to the infusion process in terms of energy.
TIP: If you can already smell the vapors from the mash outside the brewery, you have unwanted evaporation and therefore energy loss.
Lowering the heating medium flow temperature can increase the efficiency of the steam boiler and thus save energy. The heating rate of the total mash in accordance with DIN 8777 is specified as 0.5–1.0 K/min in order to keep the mashing time as short as possible. A value of 1.0–1.5 K/min applies for boiling mash. In principle, deviations are tolerable if the enzymatic processes during mashing run satisfactorily. This is checked via wort and beer analyses as well as the course of fermentation and maturation.
TIP: Check whether the mashing time represents a bottleneck in the brewing rhythm and whether the temperature of the heating medium can be lowered.
Heating to gelatinization temperature (barley malt approx. 62–65 °C) and saccharification temperature (approx. 72–78 °C) is necessary for extract solution and brewhouse yield. The lautering temperature should be as high as possible in order to keep the viscosity and consequently the lautering time low. A maximum of 80 °C may be reached, otherwise the alpha-amylase and thus the saccharification will be inactivated. There is a risk of incomplete saccharification, which shows iodine coloration and can lead to turbidity and filtration problems in the beer and increase microbiological susceptibility.
TIP: Check the insulation of your lauter tun.
Saving energy during wort boiling
Heating the wort to at least 90 °C has proven to be the best way to achieve the classic beer taste that consumers are used to. The Maillard reaction, i.e. the non-enzymatic browning reaction, is decisive for this. It is also responsible for the color and aroma of many specialty malts.
The wort is usually boiled under atmospheric pressure or overpressure so that temperatures of 95–105 °C are reached. The tasks of the process include protein coagulation, hop isomerization, inactivation of enzymes and cleavage of the DMS-P (dimethyl sulphide precursor) – processes that occur faster with increasing temperatures. This also influences the character of the beer, i.e. its taste and aroma.
The evaporation of water increases the original gravity. To save energy, however, the total evaporation should be reduced. If less water is evaporated, the amount of water used for the main and secondary pour is reduced. The aim here is to find the optimum brewhouse yield with minimal evaporation.
The smooth water usage threshold must now be observed. It describes the smooth water concentration at which the lautering process should be terminated. Further lautering of the spent grains would lead to a gain in extract, but the energy costs for evaporating the excess water would be higher than the cost savings in malt use. However, if you want to lauter for longer, the excess still water can also be used in another brew (reuse of still water).
Evaporation influences the taste of the beer. Aroma substances such as DMS, Strecker aldehydes from the Maillard reaction and hop aroma substances are evaporated. It has been shown that within 10–20 minutes many of the above-mentioned aroma compounds are largely evaporated. Longer boiling then leads to an equilibrium between formation and evaporation, so that the concentration in the wort remains the same. By pausing the boil, the temperature-related reactions can continue and the energy losses due to evaporation can be reduced at the same time.
TIP: Bring the wort to the boil, keep the wort at boiling temperature during the subsequent boiling pause without evaporating. Then boil the wort for 10–20 minutes with evaporation before knocking it out into the whirlpool.
Equation 2The facts described above apply to all cooking systems. Many different cooking systems have proven themselves in practice. Nevertheless, the parameterization of all boiling systems can be optimized to save energy. An example: With energy storage and lauter wort preheating, the evaporation of a brew should be so high that all the energy can be used to heat the next brew. There is an optimum, see equation 2 with:
• m = mass
• r = enthalpy of vaporization
• c = specific heat capacity
• T = Temperature difference between the inlet and outlet of the lauter wort at the heat exchanger
Further examples: When using a vapor recompressor, only the electricity costs during the boiling time, for example, have an impact. Reducing the boiling time usually saves little energy. In vacuum evaporation systems, evaporation is associated with cooling the wort. If there is no energy recovery system, the total evaporation should be minimized.
Process hot water that can be recovered in the brewhouse, e.g. at the vapor condenser, is often used in other areas of the brewery (e.g. cellar area, bottling, offices). The usefulness of such hot water networks should be examined here, as decentralized heat generation is often more economical.
Actually trivial: The lauter tun should be equipped with good insulation to keep radiation losses to a minimumEnergy can be saved around the whirlpool in the brewery
Hot trub separation in the whirlpool continues to keep the wort hot after wort boiling. However, as there is no heating, evaporation is severely restricted. This means that aromatic substances continue to be formed, but only a small amount is evaporated. Nevertheless, the whirlpool chimney should have an internal collecting channel to remove condensed vapors from the whirlpool, as DMS accumulates there. Without a drip tray, these vapors can flow back into the whirlpool tub seasoning.
As an example of an undesirable flavoring agent, free dimethyl sulfide (DMS) will be examined in more detail. It smells like cabbage or cooked corn. With a boiling point of 37 °C, it is very volatile and therefore odor-active. DIN 8777 requires < 100 µg/l in the whirlpool wort at half the cooling time. The detection threshold in beer is around 20–140 µg/l, depending on the type of beer. DMS is formed from the precursor S-methylmethionine in the course of amino acid metabolism during germination in the malt house. At higher temperatures, e.g. during kilning, the odorless dimethyl sulfide precursor (DMS-P) splits into odor-active, free DMS, which is evaporated. The same happens during mash and wort boiling. In the whirlpool, however, the free DMS content increases.
Normally, the DMS-P content in the wort is reduced by low DMS-P contents in the malt and by sufficient wort boiling, so that the detection threshold of the DMS in the beer cannot be exceeded when all the DMS-P is converted in the whirlpool. Alternatively, evaporation is carried out directly before wort cooling in order to keep the free DMS content in the beer below the detection threshold.
With the same total evaporation, the temperature-dependent conversion of DMS-P into free DMS can be reduced. Pre-cooling the wort during striking reduces the temperature in the whirlpool to 90 °C, for example, and has led to a reduction in free DMS of 35 µg/l in one brewery. At the same time, hop isomerization in the whirlpool is reduced, increasing the sensory quality of the bitterness in the beer.
The free DMS content is further reduced after the brewhouse as a result of desorption by the fermentation carbon dioxide. This is noticeable, for example, in the odor of the CO2 wash water before CO2 compression.
Lowering the temperature in the whirlpool reduces both the formation of DMS from its precursor and at the same time increases the sensory quality of the bitterness in the beerDetermining the minimum total evaporation
If boiling parameters are to be changed in order to save energy, the DMS content in the beer can be theoretically calculated in advance by considering the DMS-P decomposition in terms of formal kinetics.
TIP: Determine the taste threshold of free DMS in your beer.
To do this, each type of beer must be examined individually, as the matrix of the beers and therefore the detection threshold of DMS is very different. For the determination, increasing amounts of DMS are added to the beers and these are tasted.
The free DMS content in the beer must be added to this in order to obtain the detection threshold. This value should not be exceeded in the beer. Free DMS is odor-active. However, it also makes a positive contribution to the taste of the beer as long as it is below the detection threshold. A low DMS content is not a disadvantage. Incidentally, this also applies to diacetyl in beer.
Equation 3
Equation 4Accordingly, the rate constant k is calculated according to equation 4 with:
• k = rate constant
• A0 = initial concentration
• At = concentration at time t
• t = time
TIP: Measure the DMS-P content at the beginning and end of a process and determine the rate constant k of the decay according to equation 4.
By calculating the concentrations at different points in time, the course of the DMS-P over the process becomes clear. This makes it possible to determine how a reduction in the cooking time would affect the DMS-P content. In this way, potentials can be recognized and problematically high DMS contents can be avoided.
However, you must always be aware that your model is only based on the original measured values. This means that you cannot determine the factor k during boiling and simply transfer it to the whirlpool. The reason for this is the strong dependence of the DMS-P decomposition on the temperature. This is never the same everywhere on an industrial scale and can therefore never be measured precisely.
TIP: Determine the evaporation rate of DMS as a percentage, which is caused by fermentation.
Measure the free DMS content before and after fermentation. The geometry of the fermentation vessel and the fermentation process (e.g. fermentation temperature) influence the desorption of DMS from the beer. The values therefore only apply to the constellation under investigation. By knowing the detection threshold of free DMS in beer and the DMS desorption during fermentation, a value of free DMS is obtained which should not be exceeded in the wort. The whirlpool and wort boiling process steps can now be optimized.
Summary
In times of high energy prices, ways of saving energy are being sought. Optimizing energy consumption in the brewhouse is usually possible. Various methods for saving energy in the brewhouse during mashing and lautering, wort boiling and whirlpool were presented. Using the lead component DMS as an example, a calculation method was presented on how the total evaporation and thus the energy consumption can be reduced. Aspects of different boiling systems were presented.
This article is based on a technical article by Prof. Martin Krottenthaler originally published in BRAUWELT No. 27, 2023.
