How can brewers manage polyphenols in beer for better shelf life?

Today's beer consumers demand a product that maintains its quality over time, with no alterations in its clarity and appearance. Achieving a long shelf life for packaged beer depends on its colloidal stability and its resistance to microbial spoilage. Successfully striking this balance during the brewing process can be challenging, especially when considering the influence of polyphenols, which can positively and negatively affect the final beer product.

Types of polyphenols found in beer:

Flavonoids: Flavonoids are abundant in beer and play a role forming its bitterness, color and aroma. Hops, a main ingredient, contain flavonoids like catechins and proanthocyanidins. These compounds give beer its distinct taste but possess antioxidant and anti-inflammatory properties.

Phenolic Acids: Phenolic acids are a group of polyphenols found in beer, derived from malt and hops used in brewing. Examples include caffeic acid and ferulic acid. Phenolic acids contribute to the beer's flavor profile and exhibit antioxidant properties.

How do Polyphenols influence the haze and colloidal stability of Beer?

Polyphenols in beer significantly influence its colloidal stability by reacting with haze active proteins, often causing visible haze in the final product. This haze can affect the beer's shelf life as it can react with proteins and form haze in the final package over time. Therefore, it is crucial for brewers to carefully assess and implement strategies to minimize haze formation and maintain the quality of their products over time. This requires diligent management to ensure consistent quality across batches.

The impact of the brewing process on polyphenol content:

The brewing process significantly influences the polyphenol content in beer. Brewing temperature and time are crucial in polyphenol extraction. Various polyphenols are released from the malt and hops into the wort during mashing and boiling. Higher temperatures and longer boiling times can increase polyphenol extraction, though excessive extraction may introduce undesirable flavors and astringency.

Fermentation is another critical stage affecting polyphenol content in beer. Yeast activity during fermentation can modify the polyphenols present in the wort. Factors like yeast strain selection, fermentation temperature and duration can influence the final polyphenol composition of the beer. Certain yeast strains are known to have specificities in the polyphenol metabolism, resulting in unique flavor profiles.

Key factors that influence the types of polyphenols in beer include:

• Malt selection: The type and quality of malt used in brewing can significantly impact polyphenol levels as different malt levels contain varying amounts of polyphenols.
• Hop varieties: Hops contribute to a beer's bitterness and aroma and contain polyphenols.
• Brewing techniques: Factors in the brewing process, including milling technology, mash temperature, boiling time, pH levels and fermentation conditions, influence the extraction and transformation of polyphenols and adjusting these parameters can manipulate the polyphenol content in the final product.
• Ageing and storage: Polyphenols in beer can change over time due to aging and storage conditions. Oxidation, light exposure and temperature fluctuations can affect the stability and degradation of polyphenols.

How do you reduce polyphenols in beer?

Brewers use Polyvinylpyrrolidon (PVPP) to control the level of polyphenols in beer. They can use a single-use process with small PVPP particles (10-25 µm) applied at around 5- 50 g/hl or a multiple-use process with bigger PVPP particles (50-150 µm) that can be regenerated. The multiple-use process is more cost-effective for higher dosage rates. In the regeneration process, PVPP is dosed into the beer stream, separated on a filter, and then regenerated on the filter surface or candle for repeated use.

The disadvantages of using the conventional method of regenerable PVPP.

The main disadvantage of this process is the ongoing movement of the PVPP particles through dosing, stirring and pumping. This movement leads to erosion of the relatively soft PVPP particles, causing them to shrink from larger to smaller particles. As a result, the PVPP particles can pass through the filter candles or screens. The typical loss rate from a regenerable PVPP system is between 0.5 and 2%. This means, in practice, that after 50 to 200 filtrations, the PVPP has been completely exchanged. Further disadvantages of the classical PVPP stabilization technologies include significant system volumes corresponding with high pre and after-runs, high water and cleaner consumption, and high demand for de-aerated water to ensure low oxygen pick-up and storage of PVPP powder. Additionally, classical systems can only operate in batch mode, making integrating them with modern continuous operating crossflow clarification systems challenging.

Alternatives to regenerable PVPP for reducing polyphenols in Beer:

In recent years, several new approaches have been developed to overcome the disadvantages of classical PVPP stabilization:

• Implementation of a PVPP regenerable system with multiple small vessels that operate as a precoat system in an alternating mode

A PVPP regenerable system allows for continuous operation. However, the issue of PVPP loss due to erosion persists and, in some instances, is exacerbated as particle movement significantly increases with shorter batch lengths per individual filter housing.

• Usage of enzymes developed specifically from microorganisms for beer stabilization

In this case, the reaction between polyphenols and proteins is blocked. The challenge is inactivating of the enzymes in beers that are not pasteurized. Also, an additional stabilization with PVPP might be necessary for beer types with higher strength or with very long shelf-life demands.

• Stabilizers based on arabinose

Stabilizers linked with a PVP molecule as a reactive group are also utilized here. The challenge is the stability of the chemical bond between the arabinose and the PVP molecule. Also, compared to PVPP, the cost of the stabilizer materials is higher and more challenging to control. This process adsorbs proteins and polyphenols in one step, making the operation of a bypass necessary and making the system challenging to maintain.

• CBS continuous beer stabilization system

This system incorporates a well proven, regenerable PVPP in a newly developed process with a unique system design. The CBS technology is described in more detail below.

Continuous Beer Stabilization System (CBS)

The new system and process development target was to capitalize on the positive attributes and characteristics of the classical PVPP regenerable process but eliminate disadvantages like high PVPP losses, high water consumption, and cleaner consumption. A further development target was operation in batch and continuous mode at the same or a lower cost compared to classical technologies.

The CBS Concept

For the stabilizing material, well-known standard PVPP from two main suppliers is the basis. The particle size range of the standard materials has been narrowed down to better control the stabilization effect and minimize material losses. This results in higher raw material costs; however, this is offset by a significant reduction in material losses and utilities consumption.

The PVPP with a defined particle range is then immobilized in stainless steel cassettes, where it remains without movement during its entire service life, which can be several years of operation without opening the cassettes. Filling and emptying the stainless-steel cassettes takes place at the brewery. The cassettes are designed to be reused.

Between 20 and 30 cassettes are installed in a housing, representing one stabilization column. Three to six columns build a processing unit connected to a valve block and a Clean-In-Place (CIP) unit.

Three housings are combined in a system installed in parallel and connected to a valve block and a simple CIP unit.

The CBS Process

In the process, the columns are operated in an alternating sequence. Different columns switch between processing beer, regeneration, and standby. The alternating sequences, along with controlled flux variations per column, result in a continuous process with exact stabilization effectiveness.

Typically, one column is in standby or regeneration, while the other two are in operation, providing a constant output. Inside the system, the flow through each column is controlled with a flow meter and a regulation valve and varies during the stabilization process to utilize the PVPP adsorber capacity at maximum efficiency.

The system is easy to operate, with a fully automated process providing 20 standard recipes for stabilizing all types of beer. Each recipe allows the brewery to adjust parameters to ensure maximum flexibility.

The CBS System Design

The housings are sized to the CBS stainless steel cassette design, resulting in minimal hold-up volumes. The 15:1 throughput/volume ratio enables fast brand changes and minimizes beer and extract losses.

The regeneration process applies the same process steps as with classical PVPP systems, using standard caustic and acid solutions. Due to the compact design, the required quantities are reduced, which supports lower operation costs.

The system's footprint is small compared to other technologies and allows flexible positioning.

Beer Quality

Oxygen pickup from the start is minimal due to the compact design and seamless switch between de-aerated water and beer at the process start, end and brand changes.

Foam, color, haze, bitterness and taste remain unaffected with the CBS technology. Stabilization degree is controlled by selecting the relevant recipe combined with the length of the specific stabilization run between regenerations. Stabilization effect is highly constant during the entire process.

Economics

The main economic advantage of PVPP is its extremely low loss rate, typically less than 0.3% over 1000 regeneration cycles. This corresponds to a 2—to 3-year runtime before the cassette PVPP requires replacement.

A replacement is necessary when there is a slight decrease in polyphenol reduction, which occurs gradually over weeks, allowing ample time to schedule the PVPP replacement. Cassettes are reloaded at the brewery, and the stainless-steel cassettes can be used multiple times.

The system also has low water and cleaner consumption due to minimal system volumes compared to other technologies.

Experiences

The CBS technology operates in various breweries, stabilizing all kinds of beers. The cassettes have a performance warranty of 1000 regeneration cycles, which is often exceeded. The ability to run the CBS continuously makes it the ideal solution in combination with continuous crossflow clarification systems. The CBS technology fits perfectly downstream in all clarification systems. The continuous design shows its strength combined with PROFi clarification systems and other crossflow technologies.

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