Bench trials provide a systematic way to make decisions about the type and magnitude of any post fermentation adjustments will most improve a mead. Bench trials are most commonly used to evaluate how much acid, tannin, or sweetness to add to a mead in order to achieve balance. They can also be used to determine the type and minimum amount of a fining agent needed to clear a mead or amount of a spice tincture needed to achieve a desired flavor profile.
From a high level, the a bench trial consists of adding a different known amount of a substance (e.g., tannin powder, acid, etc.) to identical samples of a given mead, tasting each, choosing which sample is preferred, and then determining a dose for the whole batch by scaling up from the preferred sample. This can be easily and repeatably done by using stock solutions of a known concentration to a fixed volume of mead.
While a brewer can conduct a bench trial alone, it is highly advisable to have at least one other person participate in the trial, as each person's palette is different and having more opinions will help you to make better decisions. It is also a fantastic way to include friends and family in your hobby.
'Graduated' above refers to having volumetric markings so that you can accurately measure dosing.
Stock solutions with known concentrations are essential to the Bench Trial Process described below. The actual concentration that you will want is dependent on the sample size you choose to use. For the purposes of this guide, 1% solutions are recommended for tannins and fining agents; 10% solutions are recommended for acids. Stock solutions can be prepared in the following manner:
Note that the use of vodka in Step 1 above helps ensure that the stock solution does not significantly dilute the ABV of the samples during the taste trial. The amount of vodka used in stock solution preparation may be adjusted to more closely match the measured ABV of the mead. Distilled water can be used in place of vodka in step #1, as described in the Scott Lab Fermentation Handbook, but the resulting stock solution will not be shelf stable and should be discarded within a few days after preparation. The 50ml vodka amount listed above is recommended by /u/dmw_chef to ensure a shelf-stable stock solution that can stored and used for many bench trials.
It is important to be very accurate with the process described above. Accuracy in preparing a stock solution helps ensure that the scaled amount for the full batch produces a result consistent with the tasting trial, and that the results of one tasting trial may be used as a reference point for future batches.
Stock solutions for back sweetening trials are best mixed as needed by mixing a known weight of honey with water to a known volume; for example add 100 grams of honey and fill with hot water to 100ml and mix thoroughly. This will give you a solution with a gravity of approximately 1.3.
Dosing in bench trials is most easily expressed in parts per million (PPM), which is defined as one milligram of a substance dissolved in 1 liter of solution. Reputable manufacturers of fining agents and powdered tannins will have a recommended dosing range that can be found on the product's web site or on the Technical Data Sheet provided by the manufacturer; this range will usually be expressed in PPM (e.g., 50-200 PPM) or in grams per hectoliter (g/hL). One g/hL is equivalent to 10 PPM.
Generic wine tannins or fining agents may not have a TDS available from the manufacturer and will have either a fixed dose or a recommended range specified on the packaging, usually in grams per gallon (g/gal). Dosing expressed in this way can be converted to PPM by dividing the dose by 0.38 then multiplying by 100 (0.38 g/gal is 100 PPM). For example, for a dose of 1 g/gal, (1/0.38)*100 = 263.1 PPM. If the tannin or fining agent has a fixed dose, a reasonable range can be obtained by using 50% of the dose for the low end, and 150% for the high end, e.g. for a fixed dose of 100 PPM, a reasonable range for bench trials might be 50-150 PPM.
Dosing for acids, sweetness, or other things that do not have a recommended dosing, a 'lazy trial' can be used to ballpark a dosing range. Take a 50ml sample of the mead, and use the 1 or 10ml graduated syringe to add a small amount of stock solution to the sample. Alternate between taking a very small sip and adding a little more stock solution until you think the mead is in the ballpark of what you'd like to achieve with the adjustment. Take the total volume of stock solution added and convert to PPM using the table below, using the same 50% and 150% rule above to determine a dosing range to evaluate.
The table below provides dosing for a 1% stock solution.
One thing to keep in mind that confuses some people is that PPM is unitless - regardless of if you add 0.5ml of a 1% solution, or 0.05ml of a 10% solution to a 50ml sample, you are still adding 100 PPM of the substance to the sample. Once you have determined the PPM dose needed for the desired sensory effect, you can easily use that to determine the amount of the powdered/granulated substance used to make your stock solution needs to be added to your final volume. For metric volumes, 1PPM is 0.001 g/L so for 100PPM you'd add 0.1 g/L. For Imperial volumes, the formula is 0.38 * (Desired PPM) / 100, so for 100 PPM you'd add 0.38 g/gal and 150 PPM would be 0.57 g/gal.
Dosing for back sweetening trials is not done by PPM. Using a stock solution of honey and water with a known (or estimated) gravity you can use the blending calculator available from meadcalc to determine the volume of your stock solution to add in order to achieve target SGs for your samples.
The following process uses samples appropriate for fairly small batches of mead and is usually sufficient for two tasters. If preparing samples for more tasters, simply multiply the amounts suggested below to the desired sample size.
For tasting trials if desired, you can further refine the dosing by choosing instead the two best samples and mixing equal volumes of each to produce a sample in between each dose and repeat the tasting evaluation.
An excellent video detailing this process can be found on the Doin' The Most youtube channel