Fundamentals of Packaging. Beer Stabilisation

Transcription

1 Fundamentals of Packaging Beer Stabilisation

2 Beer Stabilisation The shelf life of any food product depends, to a large extent, on its biological stability and beer is no different. The multiplication of organisms during storage is the major cause of product spoilage. Normally filtered product ready for packaging in kegs, cans or bottles, contains some level of micro-organisms. Contamination levels vary from plant to plant. The types of organisms present also vary.

3 Beer Stabilisation The presence of most of these micro-organisms is not a health risk. Due to: The presence of CO 2. (anaerobic conditions). The low ph. The presence of alcohol. A low residual extract. Bacteriostatic compounds extracted from hop products. (beer). No health-threatening bacteria can survive for any length of time.

4 Beer Stabilisation There are however organisms that can survive and multiply in the presence of these unfavorable conditions. If left unchecked, these so called spoilage organisms affect the flavour and/or the appearance of the product. The range of such spoilage organisms includes: brewers yeast, wild yeasts a variety of bacteria.

5 Beer Stabilisation Filtered beer and beverages containing natural fruit products, also contain active enzymes. In their active state, these enzymes, can over time, adversely affect product features such as flavour and head retention (foam).

6 Beer Stabilisation: Purpose The aim of beer stabilisation is to prolong the products shelf life through the deactivation of micro-organisms and enzymes, which either spoil the product or cause undesirable chemical changes.

7 Beer Stabilisation: Principles In beer we want to achieve a biological stability (commercial sterility) with minimal effect on the physical stability of the beer. Pasteurisation aims to achieve this by utilising the minimum heating requirements. Pasteurisation should not be confused with sterilisation. Pasteurisation achieves a statistical kill rate of specific micro organisms using heat treatment.

8 Beer Stabilisation: Principles A range of techniques are used on foodstuffs to inactivate unwanted organisms: Use of preservatives* Irradiation* Heat inactivation ~ Cooking/Boiling* Heat inactivation ~ Exposure to elevated temperature** (this is called pasteurisation - pioneering work done by Louis Pasteur) Micro-filtration** * not suitable for beer and beverages due to flavour issues ** techniques favoured by the beer/beverage industry)

9 Beer Stabilisation: Principles Pasteurisation: Beer and many beverages are adversely affected by elevated temperatures, so the use of any type of heat treatment is a compromise. Pasteurisation is a relatively mild heat treatment, reducing the number of micro-organisms, with the minimum amount of change to the flavour and aroma of the product. The use of heat does have the benefit of inactivating enzymes and eliminating any product deterioration that they may cause.

10 Beer Stabilisation: Principles The following factors have an effect on the inactivation of micro organisms: Temperature Time Infection type Rate of infection Beer composition (e.g. % alcohol in beer) ph Presence of CO 2

11 Beer Stabilisation: Principles The level of pasteurisation is determined by the thermo-tolerance of the specific micro organisms that are trying to be killed. This is determined by the following two factors: The D value - decimal reduction time (minutes) This is the time needed at a given temperature to inactivate 90% of the viable micro population. The Z value temperature dependence (ºC) This is the increase in temperature required to reduce the D value by 90%.

12 t Beer Stabilisation: Principles If a homogeneous population of a given micro-organism is subjected to heat at a constant temperature, which is high enough to be lethal, it is generally found that the number of survivors will decline with time: N 0 N N = Population. N 0 = Initial population. t = Time. The N values are usually expressed as concentrations, i.e. the number of micro-organisms per ml

13 Beer Stabilisation: Principles Louis Pasteur defined the relationship for pasteurisation. He described the relationship between time and temperature as Pasteurisation Units (PU s) 1 PU is equivalent to holding the product at 60 ºC for 1 minute. The PU formula is shown below: PU = t x (T-60) PU = number of pasteurisation units t = holding time in minutes T = holding temperature in ºC

14 Beer Stabilisation: Principles The lethal death rate curve (also known as Del Vecchio s curve) is shown below and describes the number of PU s achieved per holding time period.

15 Beer Stabilisation: Principles It is possible to achieve the same lethal effect on a micro-organism population by varying temperature/time ratios. For example: 50 minutes at 53 C 5.0 minutes at 60 C 0.5 minutes at 67 C 0.05 minutes at 74 C will all achieve the same effect.

16 Beer Stabilisation: Principles 60 C has come to be accepted as the reference inactivation temperature for brewery products. Certain types of bacteria are not inactivated at temperatures below 60 C. Temperatures much above 60 C adversely effect aroma, flavour, colour and foam.

17 Beer Stabilisation: Principles Inactivation of micro-organisms does not only happen at 60 C Pasteurisation of product in-container involves gradual heating and cooling. As the temperature rises over time, it results in the accumulation of increments of PU s on the way. The same happens during the cooling process. In effect, this means that required total number of PU's can be obtained with holding the product at 60 C for no more than a few minutes.

18 Beer Stabilisation: Principles

19 Beer Stabilisation: Principles As noted earlier the composition of the product plays a role in the rate of organism inactivation. Different products require different levels of pasteurisation to ensure stability: Examples of some typical PU s: Product Lager/Pilsener Ales / Stout Low alcohol beer Non - alcoholic beer Lemonade Juices Typical PU

20 Beer Stabilisation: Principles Current thinking is that it is not necessary for pasteurisation to destroy the entire population of organisms present. (i.e. give absolute sterility ). A practical sterility aimed at eliminating just the undesirable organisms is sufficient. Some organisms such as spores, which may survive pasteurisation, will not propagate in the type of product we are discussing, and are of no functional concern.

21 Beer Stabilisation: Principles One of the most serious concerns that brewers have with pasteurization (and over pasteurization), is the effect that heat has on the flavor of the beer. We measure the Thermal Impact Units (TIU), which a measure of the total heat impact on the product rather than the pasteurisation effect on the micro.

22 Beer Stabilisation: Methods Several adaptations of these techniques are used in the industry: Tunnel Pasteurisation Flash Pasteurisation Sterile filtration

23 Beer Stabilisation: Tunnel Pasteurisers The oldest and still the most widely used method. It is the safest way to produce a biologically stable product since the product is already sealed into containers and cannot be re-infected. Use is made of a tunnel pasteuriser, which may be either single or double decked. Double deck tunnel pasteuriser

24 Beer Stabilisation: Tunnel Pasteurisers Design factors to be considered: Materials of Construction Structure and Weight Steel vs Stainless Steel Plastic vs Steel Corrosion Insulation Cleaning and maintenance Transport Systems Walking Beams Continuous Belts

25 Beer Stabilisation: Tunnel Pasteurisers Spray Systems Vortex vs Spray vs

26 Beer Stabilisation: Tunnel Pasteurisers Temperature Balance Heating Methods Heat exchangers vs direct steam PU Control How do you control PU addition Basically consists of a form of cross flow and cold water addition after long stops.

27 Beer Stabilisation: Tunnel Pasteurisers Process: The containers are conveyed from the closure machine to the infeed of the pasteuriser on slat band conveyors. On double deck pasteurisers, the flow of containers is split to ensure both decks are equally supplied with containers. Containers are transported through the tunnel using walking beams or a moving mat system.

28 Beer Stabilisation: Tunnel Pasteurisers The tunnel is divided into a series of zones, each operating at different temperatures. Zones Heating Heating Super Heating Hold Pasteurise Cooling Cooling Cooling Heat

29 Beer Stabilisation: Tunnel Pasteurisers As the containers pass through the different zones, they are sprayed with water from overhead sprays. With the zones at different temperatures the container contents are first heated then cooled. HEATING COOLING Mixing region Main core Boundary layer

30 Beer Stabilisation: Tunnel Pasteurisers During the heating phase containers are heated progressively until the desired target temperature is reached in the pasteurising zone. It is in this zone that optimal heat treatment takes place. The containers are gradually cooled from the holding temperature to the required discharge temperature. After the pasteurising process the containers leave the pasteuriser on a discharge conveyor.

31 Beer Stabilisation: Tunnel Pasteurisers The effectiveness of pasteurisation is dependent on the temperature reached by the product itself, not the temperature of the container or the water sprays.

32 Beer Stabilisation: Tunnel Pasteurisers In a liquid, heat is transferred by convection. During pasteurisation the product nearest the container wall heats up first. In bottles, a point in the centre of the lower quarter of the container is the last to heat up. This point, which is the last to reach pasteurisation temperature, is called the "cold spot.

33 Beer Stabilisation: Tunnel Pasteurisers The accumulation of PU s is measured by using a PU Recorder Bottle Recorder Can Recorder

34 Beer Stabilisation: Tunnel Pasteurisers A PU Recorder is a waterproofed thermograph that measures the internal temperature of a container* by means of a probe. During transit through the pasteuriser the Recorder logs temperature inside the container against time and calculates the number of PU s delivered. *The container is normally drawn from the production stream at the pasteuriser infeed.

35 Beer Stabilisation: Tunnel Pasteurisers To ensure effective measurement, it is essential that the lower tip of the probe is located near the cold spot in the container, rather than at some random point. Opinions vary as to where exactly this cold spot is, but it is important that the probe position is standardised to ensure consistent monitoring. Bottles : 15 mm up from the base & centralised. Cans : In the centre of the product mass.

36 Beer Stabilisation: Tunnel Pasteurisers

37 Beer Stabilisation: Tunnel Pasteurisers In the interests of energy conservation, pasteurisers are designed with what is known as a regenerative water system. Water sprayed onto cold (ex filler) containers in the first pasteuriser zone is cooled down after coming into contact with the containers. This cooled water is pumped to the last zone and used for the final container cooling. In the process of passing over the warm containers the water is warmed up. Once warmed, the water is returned to the first zone and the process repeats itself.

38 Beer Stabilisation: Tunnel Pasteurisers Zones Heating Heating Super Heating Hold Pasteurise Cooling Cooling Cooling Heat In this example Zones 1 & 7 and Zones 2 & 6 are regeneration zones.

39 Beer Stabilisation: Tunnel Pasteurisers When there is a steady flow of containers, the energy required to heat incoming containers is taken from the energy recovered during the cooling process. The pasteuriser is in a balanced condition.

40 Beer Stabilisation: Tunnel Pasteurisers When there is a gap in the container flow, there is insufficient energy available to effectively cool the containers at the discharge. The pasteuriser is in an unbalanced condition.

41 Beer Stabilisation: Tunnel Pasteurisers As the gap in the container flow passes through to the discharge end of the pasteuriser, there is insufficient energy available to effectively warm the incoming containers. Rebalancing temperatures requires additional heating.

42 Beer Stabilisation: Tunnel Pasteurisers Process Control Production: Temperature of zones During downstream stoppages: The water is recirculated within the superheat and holding zone tanks so as not to keep spraying and accumulating PU s to the standing containers, or Cold water is introduced to the cooling zones for upstream stoppages. Condition of filter screens in sumps - not blocked and/or dirty. Sump levels - not below the halfway mark to prevent pump cavitation.

43 Beer Stabilisation: Tunnel Pasteurisers Pump pressures. 50 kpa ensures proper spray profile and water flow over the containers. High pump pressures indicate blocked spray bars. Spray nozzle condition and alignment. Process Control QC: Actual zone temperatures*. PU recordings** (including difference between top and bottom decks). Transit time. Beer out temperature. Microbiological check

44 Beer Stabilisation: Tunnel Pasteurisers Advantages: The most reliable and efficient method of achieving microbiological stability. Minimal effect on product quality. Happens after the product is sealed into containers - no risk of product re-infection.

45 Beer Stabilisation: Tunnel Pasteurisers Disadvantages: Heating of any product, no matter how carefully controlled, does have an adverse effect on the product s flavour. The high internal pressures that build up in containers during pasteurisation, require the use of robust packaging. This adds to production costs. Operating costs are high in terms of energy and water usage, even with the use of heat regeneration and water reclamation. High capital and installation costs. Requires large floor area.

46 Beer Stabilisation: Flash Pasteurisation Used to pasteurise bulk product. (often in-line). After pasteurisation the product can be filled into standard containers or kegs. All operations carried out after pasteurisation (e.g. filling [including containers] and sealing) need to be sanitary/sterile to avoid the risk of re-infection.

47 Beer Stabilisation: Flash Pasteurisation The principles of pasteurisation (applying heat to destroy micro-organisms, followed by cooling) are the same as for the in-container process. Pasteurising temperatures are however higher and exposure times much shorter. Flash Pasteurisation is carried out in a specially designed plate heat exchanger. When operated in-line the use of a buffer tank is necessary. This adds a further re-infection risk.

48 Beer Stabilisation: Flash Pasteurisation

49 Beer Stabilisation: Flash Pasteurisation

50 Beer Stabilisation: Flash Pasteurisation 1 C 63 C 70 C 1 C

51 Beer Stabilisation: Flash Pasteurisation Heating Section. Uses a counter-flow plate heat exchanger to heat beer from 0 C to ±70 C in a short space of time using hot water. Holding Tube. A length of stainless steel tubing wound into a serpentine coil. This is the pasteurising section of the unit; the tube holds the heated beer for the required holding time (+ 30 seconds) prior to cooling.

52 Beer Stabilisation: Flash Pasteurisation Cooling Section. In this section, beer gives up heat to the cooling media (glycol) and is chilled back to the temperature required for filling. Regeneration Section. In this section, the hot pasteurised beer is used to preheat the beer entering the pasteuriser. This accomplishes 3 things: The incoming beer is preheated to ±90% of the required pasteurisation temperature. The pasteurised beer is cooled down to a temperature that is only a few degrees away from the filling temperature. Allows for the reduction in size of the heating and cooling heat exchangers.

53 Beer Stabilisation: Flash Pasteurisation Advantages: Simpler, more easily controllable, than in-container pasteurisation. Heat exchanger achieves uniform pasteurisation temperatures and produces lower discharge temperatures. Low product DO s and short pasteurisation time minimises the possibility of oxidation. Equipment has low capital and operating costs, requires little maintenance. Plant is relatively small and has a low energy consumption. Lightweight containers can be used.

54 Beer Stabilisation: Flash Pasteurisation Disadvantages: The entire product handling system, after the pasteuriser, needs to be sterile Condensation on filled containers presents a labelling problem A stop-start filler operation adversely affects the process. A filler stoppage means product must be diverted to a buffer tank. In the event of the tank already being full, product circulates in the pasteuriser and gets overheated. Regular microbiological checks need to be carried out Regular cleaning of the exchanger plates is necessary Gas break out

55 Beer Stabilisation: Sterile Filtration A totally different method of achieving biological stability micro-organisms are physically filtered from the product, rather than being destroyed by heating The two main types of sterile filtration in practice today are: Membrane filtration Cross Flow filtration

56 Beer Stabilisation: Sterile Filtration Like flash pasteurisation, sterile filtration occurs before the product is put into package and thus there are risks of infection still occurring downstream of the sterile filler.

57 Beer Stabilisation: Sterile Filtration Membrane filtration uses 4 mechanisms for separating suspended solids from liquids: Direct interception The particles are trapped by the gaps in the cartridge membrane pores Charge effects the separation method relies on particles having small electrostatic charges which then bond with the filter media

58 Beer Stabilisation: Sterile Filtration Inertial impaction Inertial impaction occurs due the tendency of particles to travel in a straight line as compared to the fluid which takes the path of least resistance through the media and will divert around the fibre. Diffusional interception Diffusional interception utilises the random movement of particles (Brownian motion) to enable the particle to deviate from the direct path through the septum and to collide with the media where the particle is retained.

59 Beer Stabilisation: Sterile Filtration The key features, which effect filtration, are: Pore geometry Membrane thickness Surface charge* * The last mechanism mainly works where the fluid is a gas.

60 Beer Stabilisation: Sterile Filtration Filter Types A wide range of cartridge types are available. The cartridges can either have a cylindrical or disc format, and are sometimes back-washable. There are two main concepts for filter media design: Non-fixed pore filter media Fixed pore filter media

61 Beer Stabilisation: Sterile Filtration Non-fixed pore filter media Non-fixed random-pore-size medium filters, such as felts, woven yarns or packed fiberglass, are constructed of media that contain pores of various dimensions that can enlarge as flowrate and differential pressure change. These types of filters are subject to particle unloading, channeling, and media migration.

62 Beer Stabilisation: Sterile Filtration Fixed pore filters Fixed pore filters are made up of either several layers of filter medium or a single thick layer. These filters work mainly on direct interception with some adsorption by inertial impaction and mainly with gases by diffusional interception. The pore size can be larger than the removal rating; however the pore size is controlled during manufacture. This combined with sufficient depth enables release of collected particles to be minimised.

63 Beer Stabilisation: Sterile Filtration

64 Beer Stabilisation: Sterile Filtration Cross filtration involves the pumping of the unfiltered product tangentially to a membrane which allows the product to pass through and stops product solids i.e. protein, yeast and bacteria.

65 Beer Stabilisation: Sterile Filtration

66 Beer Stabilisation: Sterile Filtration

67 Beer Stabilisation: Sterile Filtration CIP ing: The objectives of the CIP are not only to remove any material embedded in the filter medium, but also to sanitise the filter itself. Some trap filters are now designed so that they can be backwashed at flow rates up to 1.5 x the standard filtration rate. Alternatively these filters can be cleaned in the forward flow mode, either with hot water or sodium hydroxide. It is important not to force particles through the filter media such that they are released into the product stream during subsequent filtrations.

68 Beer Stabilisation: Sterile Filtration Advantages: Has no adverse effect on beer taste or odour since no heat is used. The end product is particularly bright /clear. Mechanical simplicity. Equipment has low capital and operating costs, requires little maintenance. Filter requires little floor space and and uses little energy. Lightweight containers can be used.

69 Beer Stabilisation: Sterile Filtration Disadvantages: The requirement for absolute sterility during the filling operation. Only short runs are possible. A great deal of time is needed for flushing, re-packing and sanitising the filters. Quality of the filters and the expertise and care used when packing and sanitising the filter is important. Membrane screens are expensive and their life-span is dependant on the number of organisms in the beer.