Display Title

Sensory Analysis​-16 Hop Grind Sensory Evaluation Method​

​​The hop grind method is a standardized, more precise alternative to the common “hop rub” method for evaluating hop sensory aroma characteristics. It is quick, clean, repeatable, and uses less sample mass compared to the hop rub method. This technique can be used by brewers for evaluating hops at harvest and throughout the year, as well as vendors, breeders, and researchers for various other purposes.

​​Sensory analysis requires standardization to minimize any variation that could cause inconsistencies in results. Hops are a non-homogenous flower that can be ground into a homogenous powder for sample assessment. The hop rub method is insufficient due to the inconsistencies of one individual’s rubbing technique. Varying pressures, body temperatures, and duration will affect the volatile compounds released from a hop sample which may lead to inconsistent results. Additionally with the hop rub method, insufficiently cleaned hands between sample assessments result in significant carry-over; this problem is eliminated by using the Hop Grind method. By standardizing the hop sample preparation using the hop grind method, consistency in the aroma compounds being evaluated by multiple assessors can be achieved.

The blade grinder is used because it has the appropriate mechanical action for grinding and mixing hop matter, be it whole cone or pellet. A burr grinder has a crushing mechanical action which is insufficient for the purpose of this method. Amber glass jars are used to prevent ultraviolet damage, and therefore sensory changes, to the hop samples.​

Sample Preparation:

• The ASBC Hop Grind Method directs the technician to prepare each sample individually for assessment. If preparing replicate samples for a single session, it is suitable to prepare a bulk sample. The total mass is calculated by multiplying the number of samples needed by grams per sample. Be sure to mix the bulk sample with a spoon before aliquoting into separate jars.
  
• Do not use a burr grinder for sample preparation.
• When grinding whole cones, do not fill the blender completely. Allowing some space helps grinding efficiency.
• If hops are not grinding well, try removing hop matter from the grinder and pulsing the blade. Higher moisture hop cones will often need to use this technique.
• Depending on the grinder, extended use can cause the grinder to heat which will transfer to the hops during preparation which could alter the aroma compounds. Do not expose hops to a warm or hot grinder. Allow the grinder to cool down before proceeding.
• The resulting samples from the grind should be visually homogeneous, a fine and even powder. Use Sensory 16 method photos for a visual reference. Under-grinding results in an inconsistent and non-homogenous sample. Over-grinding results in sample warming which melts waxes and resins in the hop and causes the sample to compress into an ineffective and inconsistent paste.
• If preparing a large number of samples in advance, place ground hop samples into the freezer and remove them prior to the evaluation session to allow them to warm up to room temperature for sensory assessment. It is recommended that samples are assessed within 8 hours of grinding and freezing.
• To preserve freshness, vacuum seal and freeze leftover unground hop material to use at a later date. If possible, purge the bag with an inert gas such as nitrogen before vacuum sealing.

Cleaning:

• Always unplug the grinder before cleaning and follow any additional safety precautions detailed in the grinder manual.
• Do not spray the grinder directly. Clean the grinder out with a dampened cloth saturated with the cleaning agent.
• When cleaning the grinder between samples, use only what isopropyl alcohol is needed to get the job done. Isopropyl alcohol has a strong aroma and can interfere with an evaluator's sensory assessment. Allow instrumentation to dry completely before preparing the next sample.
• One alternative to using isopropyl alcohol for cleaning is 70% ethanol. Ethanol has a more mild aroma than isopropyl alcohol and will interfere with sensory evaluation less. Grain alcohol can be purchased and diluted down as another alternative to isopropyl alcohol (70mL ethanol with 30mL distilled/deionized water).
• There may be other non-flammable cleaning agents appropriate for cleaning the grinder between hop samples. When evaluating other cleaning agents, in-house verification of its efficacy is necessary. There must be no carryover of the sample or residual cleaning chemical.
• If preparing a large number of samples, in lieu of cleaning one blender every time between samples, technicians may consider ordering additional blades and blender cups to increase throughput and reduce preparation time.

Sample Evaluation:

• Evaluation of hops using the grind method does not require rubbing. Instruct assessors to simply open the jar and smell. Shaking of the jar with the lid on before evaluation can increase volatilization of aroma compounds. Whether or not the shaking technique is employed, all assessors should be consistent with their protocol. This should be communicated clearly prior to evaluation.
• Be aware that samples contain fine particulates that may be ingested through the nose if the assessor inhales too deeply. This can cause discomfort for the assessor and may interfere with subsequent sample evaluations.
• It is strongly suggested to label the jars or both the jars and the lids with sample numbers when preparing or presenting multiple samples during one session.

A big thanks to…

Emily Del Bel, Jeff Daily, Janelle Harmon, Tiffany Pitra, Libby Stahl and Katie Fromuth.