DE19622551A1 - Reducing nitrosamine formation during oast-drying of green malt for brewing - Google Patents

Abstract

A method for reducing nitrosamine formation during the oast-drying of malt comprises changing the position of the circulating air (UM) vent or the position of the (UM) and fresh air (ZU) vents in order to alter the amount of exhaust air (AB) present in (ZU). Vent position is changed depending on the concentration of nitrogen oxide in the air and/or the air temperature.

Description

The invention relates to a method in which nitrosamine formation by nitrogen oxides in the exhaust air when kilning green malt, d. H. drying green malt, is reduced, according to the preamble of claim 1.

In order to convert green malt into a storage-stable state, the chemically complete biological implementations and the composition of the malt To determine, water must be extracted from the green malt. The deprivation of water is now done by drying the malt. The drying process, simplified referred to as Darren, is divided into two steps, the withering and the Darren. If the malt is dark, it is also roasted.

When wilting, the green malt is reduced to one at low temperatures Dried water content of approx. 10%. The supply air temperature is generally from 40 ° C increased to 65 ° C. The darring is after the swell. The The temperature of the supply air is increased from 65 ° C to 90 ° C (for light malt). The drying process is in the malt with a water content of 1.5 to 4% completed. With dark malt, water content at the end of the drying process 5% of the malt, roasted with a supply air temperature of 100 to 105 ° C.  

The following process parameters are decisive for the type and quality of the malt:

• - supply air volume flow,
• - water content in the air (relative humidity),
• - supply air temperature,
• - drying time.

These sizes are generally controlled by:

• - fan power or throttle valves,
• - Heating capacity,
• - Circulating air percentage.

In addition, there is a humidification or dehumidification of the for better process control Supply air, which is generally not done for cost reasons.

So-called malt kilns are used to produce malt from green malt. Various systems are used, which are called direct (with Combustion gases) or indirectly (with warm air or similar). "The essential kiln constructions are based on the order of the hordes and Loading heights: horizontal or facing with 1, 2 or 3 trays, vertical darren; Nowadays, high-performance kilns predominate with a horde or two or side by side hordes "(Narcissus, L .: demolition of the brewery. 6th edition, Ferdinand Enke Verlag, Stuttgart 1995). Systems with more than two hordes or combined systems are used. The combined systems can be derived from the different types of germination boxes.

Fig. 1 shows the flow diagram of a single-tray high-performance ratchet. This scheme is used to illustrate the basic processes and terms involved in kilning. The outside air (AU) is drawn in and preheated via a cross-flow heat exchanger (KWT). The fresh air (FR) is mixed with the recirculated air (UM) and conveyed to the pressure chamber as mixed air (MI) by means of the blower through the heat exchanger (WAT). The supply air (ZU) flows from the pressure chamber through the horde and the green malt to be dried and becomes exhaust air (AB). Part of the exhaust air is added to the fresh air as recirculated air (UM), the other part, the exhaust air (FO), is led outside via the KWT.

Controlling the air condition is crucial for the type and quality of the malt below (ZU) and above the horde (AB) during the entire drying process.

Depending on the malt, quick or slow drying is desirable, with high or low temperatures. The temperature curve of the supply air is mostly through that desired malt specified (Narcissus, L .: The brewery. 2nd volume, 6th edition, Ferdinand Enke Verlag, Stuttgart 1976). The drying speed required accordingly adjusted over the air humidity. This in turn is supported by the Circulating air proportion adjusted. Furthermore, especially at high supply air temperatures and low humidity, such as B. when stiffening, to save energy Recirculation mode preferred. For these reasons, multi-hordes are also used hot, dry Darrabuft or a part of it used as smoldering air.

As has been known for a few years, nitrogen oxides are present in the supply air of the kiln at higher temperatures (T <60 ° C), for nitrosamine formation in green malt (Flad, W .: Minimizing the nitrogen oxide concentration in the drying air of malting kilns for the purpose of producing low-nitrosamine malt. Technical University of Munich, dissertation, 1987). Out for this reason, directly heated kilns are no longer used today.

As it turned out, however, at higher temperatures (T <50 ° C) Nitrogen oxides released from the green malt, which can be detected in the exhaust air. If this exhaust air is then used as circulating air, it can turn into one Formation of nirosamine in the malt.

The formation of nitrosamine in malt is today often caused by sulfurization, i.e. H. burn down elemental sulfur in the fresh, mixed or supply air reduced. This However, a procedure is not permitted under the German Purity Law.

The object of the invention is to develop a method in which the Nitrosamine formation in the malt due to nitrogen oxides in the exhaust air is largely avoided becomes stronger, while saving energy and without the malt quality absolutely necessary to influence.  

This object is achieved by a method with the feature of claim 1. In it, the proportion of circulating air is by a suitable device, for. B. a motor-controlled air recirculation flap, regulated and limited according to requirements, with the control system having first priority over the drying program. The regulation of the proportion of recirculated air is controlled by a NO _x measurement in the supply air or / and recirculated air or / and extract air or a temperature measurement in the supply air or / and extract air or / and recirculated air.

When controlling the proportion of recirculated air in the supply air only via a Temperature measurement is the proportion of recirculated air at supply air temperatures of more than 50 ° C and a circulating air or exhaust air temperature greater than 30 ° C, between 0 and 40%.

When controlling the proportion of circulating air via nitrogen oxide measurement in the circulating air and / or the supply air is the proportion of recirculated air at a supply air temperature of more than 50 ° C Set so that the nitrogen oxide concentration in the supply air is less than 80 ppb.

By carrying out a process according to claim 1 when drying Green malt minimizes the formation of nitrosamines by nitrogen oxides in the ambient air with simultaneous energy saving compared to pure outside air operation, and without influencing the malt quality more than necessary. Furthermore, one is Sulfurization of the supply air is not necessary. By eliminating the sulfurization becomes increased wear due to corrosion on the duct walls and internals and the blower avoided. On the other hand, the German Purity Law can be observed for beer.

The exemplary embodiments of the invention are shown in FIGS. 2 to 5, with a single-level high-performance ratchet being selected. The arrangement and number of system-specific components and the air flow can be varied as desired within the scope of what is technically sensible, without affecting the effectiveness of the invention. Also, the exhaust air from one batch does not necessarily have to be used as supply air from the same batch, as in the single-tray high-performance kiln. It can also be used as recirculation for another batch, e.g. B. Darrabuft of batch 1 as recirculating air for batch 2.

Embodiment 1

Fig. 2 shows the circuit diagram for reducing the formation of nitrosamine in the first exemplary embodiment. The position of the air recirculation flap during the drying process is regulated by the desired course of drying of the green malt according to the current state of the art via a control unit and a servomotor. Another control with priority is applied to this control of the air recirculation flap position. This regulation has as input variables the nitrogen oxide concentration in the supply air (e.g. to be measured by means of a NO _x analyzer from Eco Physics with a digital measurement output) and the supply air temperature. B. a Ni-Cr-Ni thermocouple can be used. If the NO _x concentration in the supply air exceeds 80 ppb and the supply air temperature is greater than 50 ° C, the flap is closed gradually, for example every 10 minutes, by 10%. If the nitrogen oxide concentration in the supply air is less than 80 ppb, the flap is no longer closed.

Embodiment 2

Fig. 3 shows the circuit diagram for reducing the formation of nitrosamine in the second exemplary embodiment. The position of the air recirculation flap during the drying process is regulated by the desired course of drying of the green malt according to the current state of the art via a control unit and a servomotor. Another control with priority is applied to this control of the air recirculation flap position. This regulation has as input variables the nitrogen oxide concentration in the circulating air (e.g. to be measured by means of a NO _x analyzer from Eco Physics with a digital measuring output) and the supply air temperature. B. a Ni-Cr-Ni thermocouple can be used. If the NO _x concentration in the recirculating air exceeds 80 ppb and the supply air temperature is greater than 50 ° C, the flap is closed gradually, for example every 10 minutes, by 10%. If the nitrogen oxide concentration in the circulating air is less than 80 ppb, the flap is no longer closed.

Embodiment 3

Fig. 4 shows the circuit diagram for reducing the formation of nitrosamine in the third exemplary embodiment. The position of the air recirculation flap during the drying process is regulated by the desired course of drying of the green malt according to the current state of the art via a control unit and a servomotor. Another control with priority is applied to this control of the air recirculation flap position. This regulation has as input variables the nitrogen oxide concentration in the supply air and the recirculated air (e.g. to be measured by means of a NO _x analyzer from Eco Physics with a digital measurement output) and the supply air temperature. B. a Ni-Cr-Ni thermocouple can be used.

There are two cases for the priority control of the air recirculation flap position differentiated:

• a) The nitrogen oxide concentration in the circulating air is greater than 80 ppb and the NO _x concentration in the supply air is lower than that in the circulating air and greater than 80 ppb. At the same time, the supply air temperature is greater than 50 ° C, then the air recirculation damper is closed gradually, for example every 5 minutes by 10%. If the nitrogen oxide concentration in the supply air is less than 80 ppb, the flap is no longer closed.
• 20 b) The nitrogen oxide concentration in the circulating air is greater than 80 ppb and the NO _x concentration in the supply air is the same or greater than that in the circulating air, then there is no change in the damper position specified by the drying diagram.

Embodiment 4

Fig. 5 shows the circuit diagram for reducing the formation of nitrosamine in the first embodiment. The position of the air recirculation flap during the drying process is regulated by the desired course of drying of the green malt according to the current state of the art via a control unit and a servomotor. In this control of the air recirculation flap position, a further control with priority is activated, which is purely temperature-controlled. There are temperature sensors, for. B. Ni-Cr-Ni thermocouples, so mounted in the supply and recirculated air channels that the temperatures in the supply and recirculated air are detected and passed on to a control unit. The control unit changes the flap position by controlling the air recirculation flap servomotor without taking into account the flap position specified by the drying program. In this case, if the supply air temperature is greater than 50 ° C and the circulating air temperature is greater than 30 ° C, the proportion of circulating air is limited to 0 to 40% of the supply air, depending on the kiln design.

Claims (17)

1. A method for reducing the formation of nitrosamine in the malt when kilning malt, characterized in that the position of the recirculating air flap or the recirculating air and the outgoing air flap for setting the proportion of recirculating air in the supply air in addition to the position required by the drying process by means of a further control with 1. Priority is changed. The nitrogen oxide concentration in the air and / or the temperature of the air are used as the input variable for this additional control. 2. The method according to claim 1, characterized in that the control of the recirculating air flap position uses the temperature measurement in the recirculating air as an input variable. Here, z. E.g .: T _UM <30 ° C, then closing the flap. 3. The method according to claim 1, characterized in that the control of the recirculation flap position uses the temperature measurement in the exhaust air as an input variable. Here, z. E.g .: T _AB <30 ° C, then closing the flap. 4. The method according to claim 1, characterized in that the control of the recirculation flap position uses the temperature measurement in the supply air as an input variable. Here, z. E.g .: T _CLOSE <50 ° C, then closing the flap. 5. The method according to claim 1, characterized in that the control of the recirculation flap position uses the temperature measurement in the recirculating and supply air as an input variable. Here, z. For example: T _UM <30 ° C and T _CLOSE <50 ° C, then close the flap. 6. The method according to claim 1, characterized in that the control of the recirculation flap position uses the temperature measurement in the exhaust and supply air as an input variable. Here, z. E.g .: T _DOWN <30 ° C and T _CLOSE <50 ° C, then closing the flap. 7. The method according to claim 1, characterized in that the control of the recirculation damper position uses the nitrogen oxide concentration in the supply air as an input variable. Here, z. E.g .: c _{NOx, ZU} <80 ppb, then closing the flap. 8. The method according to claim 1, characterized in that the control of the recirculating air flap position uses the nitrogen oxide concentration in the recirculating air as an input variable. Here, z. E.g .: c _{NOx, UM} <80 ppb, then closing the flap. 9. The method according to claim 1, characterized in that the control of the recirculation flap position uses the nitrogen oxide concentration in the exhaust air as an input variable. Here, z. E.g .: c _{NOx, AB} <80 ppb, then closing the flap. 10. The method according to claim 1, characterized in that the control of the recirculating air flap position uses the nitrogen oxide concentrations in the supply and recirculating air as an input variable. Here, z. For example: c _{NOx, UM} <80 ppb and c _{NOx, UM} <c _{NOx, ZU} and c _{NOx, ZU} <80 ppb, then close the flap. 11. The method according to claim 1, characterized in that the control of the recirculation flap position uses the nitrogen oxide concentrations in the supply and exhaust air as an input variable. Here, z. For example: c _{NOx, AB} <80 ppb and c _{NOx, ZU} <80 ppb, then close the flap. 12. The method according to any one of claims 7-11, characterized in that the control of the recirculation flap position also uses the temperature of the supply air as an input variable. The condition T _CLOSE <50 ° C should also be fulfilled. 13. The method according to any one of claims 7-11, characterized in that the control of the recirculation flap position additionally uses the temperature of the recirculation air as an input variable. The condition T _UM <30 ° C should also be fulfilled. 14. The method according to any one of claims 7-11, characterized in that the control of the recirculation flap position also uses the temperature of the exhaust air as an input variable. The condition T _AB <30 ° C should also be fulfilled. 15. The method according to any one of claims 7-11, characterized in that the control of the recirculation flap position also uses the temperatures of the supply and recirculation as an input variable. The conditions T _ZU <50 ° C and T _UM <30 ° C should also be fulfilled. 16. The method according to any one of claims 7-11, characterized in that the control of the recirculation flap position also uses the temperatures of the supply and exhaust air as an input variable. The conditions T _ZU <50 ° C and T _AB <30 ° C should also be fulfilled. 17. The method according to any one of claims 1-16, characterized in that the Exhaust air or part of the exhaust air of a batch as supply air or supply air proportion of a another batch is used.