Providing a quality chemical analysis service for regional hop growers and craft beer brewers in the Midwest.
Dry-Matter and Moisture Testing
Determining Temperature and Time Settings
Some time, shortly after supper, place a one-quart, sealable, plastic, storage bag on a scale that measures to at least the nearest gram. Determine the weight of the empty plastic bag to at least the nearest gram (tenth-gram if you can) and record the value in a notebook you plan to keep handy. Collect a test sample of fresh hop cones that will comfortably fill the plastic bag, yet still allow it to properly seal shut. Place the filled and sealed bag on the scale and determine the weight of the filled bag to at least the nearest gram (tenth-gram if you can) as you did before. Carefully (meaning "without spilling or losing any") place all of the hop cones in the dehydrator and set the temperature-controller to a low setting (between 100° and 120° Fahrenheit). Record the temperature setting and the starting time in your notebook. Go to bed and get a good night's rest.
After 12 hours in the dehydrator, carefully remove
the hop cones from the dehydrator and place them all back in the plastic bag. Seal
the bag and allow the hop cones to cool to room temperature. (If not sealed, the hop
cones may actually pick up some weight as they absorb
a little moisture from the atmosphere.) Measure the weight of
the sample as you did previously and record both the weight and time. Return the
sample to the dehydrator and repeat the cooling, weighing and recording step again
after a few hours. Continue cooling, weighing and recording the weight and time
every couple of hours until there is no detectable change in the weight. When you
get the exact same weight twice in a row, you have found the dry-matter weight, the
temperature setting and the time (use the final time!) required to dry fresh hops.
Are They Really Dry?
At lower drying temperatures and humid weather conditions, the hop cones will have a tendency to hang on to the last bit of moisture and not get to the 0% moisture point. At higher temperatures the more volatile (more easily evaporated) essential oils will be driven off with the moisture, causing your calculated moisture content to include all of the moisture and some of the essential oils.
You could repeat the above process at increased drying temperatures to find the temperature where drying appears to be completed in the shortest time, but then you also run the risk of driving off some of the essential oils and getting a misleading result from "over-drying" your hops.
Our suggestion is to collect two samples for drying. Dry one as you would normally do (above) and send the other in for moisture determination by either the Distillation Process (preferred for accuracy) or the Forced-Air Drying-Cabinet Process (lower cost but still quite accurate). Doing this once will allow you to understand how your drying method compares to a lab analysis method. If you find that your moisture value is one or two percentage points lower than the laboratory result, you will know that your process is typically leaving that percent of moisture remaining in the hops. In the future, you can add that difference to your home moisture results and be confident that they are close to the actual "sent-to-the-lab" results. It is best to under-dry the hops rather than over-drying them. However, whatever you do, follow this primary rule of scientific measurement: Be Consistent!!!
Essential Oil Testing
Testing for the essential oil content of your hops is very similar to testing for the moisture content. In fact, you have already begun the process by driving off the moisture content. Begin when you, or someone else, will be around the kitchen and able to keep an eye on the oven for a few hours. Start with the sample of thoroughly dried hops you have carefully saved from the moisture test. Carefully reweigh the plastic bag with the thoroughly dried hops and record the weight, be sure it is all there. (If not properly sealed, they will actually pick up some weight as it absorbs a little moisture from the atmosphere.) Turn your kitchen oven on to a temperature setting of about 210°F) and allow it to preheat.
While the oven is pre-heating, spread the entire hop sample out on a large baking sheet, preferably with edges to keep the hops from falling off the sheet and catching fire on the bottom of the oven. (Unwanted fires are generally considered a "bad laboratory technique"! ☺ )
When the oven is ready and your tray of hops is ready, carefully slide the tray into the oven and record both the temperature setting and the time. Allow the hops to remain in the oven a couple of hours before carefully removing them. Let them cool to a point where they are still warm, but not burning hot to the touch and place them back in the plastic bag. Allow them additional time to cool to room temperature. Once cool, weigh the sample and record the weight, time and temperature settings, as before. Carefully spread the hops out on the tray again and place them back into the oven for another hour or so. Continue cooling, weighing and recording the weight and time, every hour or so, until there is no detectable change in the weight. When you get the exact same weight twice in a row, you have found what we will call the "oil-free" weight. Record the temperature setting and the time (use the final time!) required to reduce your dried hops to the "oil-free" state.
Final Sensory Testing
Place a few cone remnants in your hand, crunch them up, rub them around, smell them and taste them, then write down your impressions in your notebook. Turn off the stove and add your "oil-free" hop cones to the compost pile.