Hop preservation requires attention to four factors: oxygen, temperature, light, and humidity.
Oxygen is the primary enemy of hops. It can oxidatively polymerize alpha acids, causing them to lose their original flavor and antimicrobial properties. Polymerized resins, such as gamma resin, contribute to the bitterness of hops. The oxidation of high molecular weight polyphenols in hops results in a harsh bitter taste in beer. Additionally, the oxidation of aroma compounds in hops leads to the loss or alteration of their characteristic aromas, although sometimes the oxidized hops may exhibit noticeable ester aromas. To prevent oxygen exposure, vacuum or nitrogen-filled packaging is commonly used.
Hop pellets, particularly those with high oil content, are often compressed into dense pellets that are resilient and difficult to break apart, making them less desirable for usage. As a result, this type of packaging has become less common.
Nitrogen is used to fill aluminum foil bags, ensuring that hop pellets do not clump together and facilitating ease of use.
It is worth noting that oxidized hops should not be discarded without consideration. Instead, they can be used sparingly as a fragrant addition during the final stages of boiling for wheat brewing.
The recommended storage temperature for hops should not exceed 4°C. Temperatures above this threshold significantly reduce alpha acid content and promote the formation of gamma resin, leading to increased bitterness and adversely affecting hop quality. No lower temperature limit is required, but lower temperatures help maintain the original quality of hops. Shelf life can reach up to five years when stored below 0°C.
Freezing hops well below 0°C can alter their morphology. Hop pellets contain approximately 8% moisture, which expands when frozen. When the temperature returns to normal, the pellets quickly disintegrate and oxidize upon contact with air. Therefore, it is advisable to store hops at temperatures between 0-2°C. Packing hops into smaller, easily usable packages at lower temperatures can prevent breakage and oxidation during retrieval from larger bags.
Exposure to light causes hops to change color to an off-white shade and leads to significant loss of aroma compounds. As a result, all hops available in the market are packaged in aluminum foil bags. If an aluminum foil bag is not available for repackaging, a transparent ziplock bag can be used along with black paper wrapping.
When storing hops, it is important to maintain a relative humidity of no higher than 60%. Excessive humidity can result in:
– Polymerization of alpha acids to form gamma resin, resulting in increased bitterness;
– Growth of mold and bacteria. Hops have potent antimicrobial properties against most gram-positive bacteria but are less effective against gram-negative bacteria and fungi;
– Rotting of plant tissue in a moist environment.