Dosing unit conversion table: g/hL, mL/hL, drops

g/hL, g/L, mL/hL, units per hectoliter, microliters in a glass, drops in a bottle, US gallons: seven ways of writing the same dosing decision. It is the first source of error we see in the cellar, and it costs money in both directions.

This page brings together every conversion you need, as tables. For each one we also show which AMEDEE Lab tool does it for you, because the surest way not to get a calculation wrong is still not to do it in your head.

The short way: let the tool convert

The three AMEDEE Lab tools are free, need no account, and run on the same figures as the tables on this page.

• Drop test: enter what you put in your trial glass or bottle, and it returns the dose in all five formats (liquid tannin, powder tannin, chips, 7 mm and 18 mm staves) and the total quantity for your tank.
• Oak simulator: your volume, your wine, your target. It returns a dose in g/hL or in units per hectoliter, a contact time, and compares chips, staves and inserts on the same tank.
• Barrel diagnostic: it converts the age and history of a barrel into remaining potential, then into a number of 22 mm sticks to put back in.

If you would rather understand the calculation before handing it to a tool, the tables below give you everything.

Table 1: concentration units

Two rows deserve a comment. First: scientific literature often works in grams per liter, oenological documents in grams per hectoliter. The useful range of our oak conversion table, 100 to 600 g/hL, corresponds to 1 to 6 g/L, inside the 2 to 10 g/L doses reported by the IFV (French Vine and Wine Institute) for oak wood pieces. A factor of one hundred gets noticed late: check the unit before you compare.

The second is the one that does real damage. Our liquid tannins are concentrated at 20%: one liter of liquid equals 200 g of powder. The finishing tannin column of the table is expressed as powder. Dosing 4.7 mL/hL of liquid for a 4.7 g/hL target delivers five times less than planned. Applying to a powder a value meant for a liquid multiplies the dose by five, and that cannot be undone: you do not take a tannin back out of a tank.

Table 2: from the trial glass to the tank

A trial is run in microliters or drops, a tank is dosed in mL/hL. Going from one to the other is simple, provided you know the volume of the container and the volume of a drop. We count 50 µL per drop, the value used by the drop test.

The key word is "raw". A tannin tasted right after the addition shows only part of what it will give once integrated. In the model behind our drop test, for a standard-profile red at pH 3.5 and 20 °C, what you perceive on the day of the addition is worth about a quarter of what the same dose will give after fourteen days. 100 µL tasted straight away in a 10 cl glass therefore correspond to about 25 mL/hL in the tank, not 100. On a white, the factor is close to one half. It also moves with the wine profile, the pH and the temperature.

This factor cannot be worked out in your head, and it explains a good share of overdosing: you taste too early, find it is not enough, and multiply. The drop test applies the correction for you, and offers two modes: an express estimate in the glass, indicative only, and a bottle trial left to rest for two weeks, which is the one to decide on.

Table 3: from one format to another

Our oak conversion table gives, row by row, the equivalences between chips, staves and tannins for the same level of oak. It rests on fixed coefficients, shown here for 100 g/hL of fine chips.

Three points to watch. A 7 mm stave and an 18 mm stave do not weigh the same: the two columns are calibrated separately on the same level of oak, and one cannot be derived from the other by a rule of three. The white and red columns are not read on the same row: the new barrel equivalent is reached around 350 g/hL on a white and around 500 g/hL on a red. Finally, changing format changes the time: going from chips to an 18 mm stave means going from one month to seven.

The oak simulator does these three conversions at once: for your tank, it sets the dose and the duration of each format side by side.

Table 4: from barrel to inserts

A barrel releases about 60% of its oenological capital in its first year. What remains afterwards converts into inserts, and these are the benchmarks we use in wine.

These benchmarks were established in wine and do not transfer to spirits. In between, everything depends on the real age of the barrel and what it has already given: that is the calculation run by the barrel diagnostic, barrel by barrel.

Table 5: US units and harvest

In US documents, mg/L are often written as ppm. The drop test and the oak simulator accept a volume in thousands of US gallons directly, and the drop test also accepts a harvest tonnage: it applies the 7.5 hL per metric ton yield shown above. If your actual yield is different, enter the volume instead.

A complete example, on a 250 hL tank

Target: new barrel equivalent on a white, i.e. 350 g/hL of fine chips.

Five numbers, a single target level of oak. Look at the 7 mm stave row: the table shows 1.8 u/hL, which is 1.75 rounded. Multiplying the rounded value gives 450 staves, rounding again to 2 gives 500, which is 14% more wood than the exact calculation. The tools only round at the end, on the number of staves.

The habit that prevents all this

Write the unit next to the number, always, including on the sheet taped to the tank. Most of the overdoses reported to us do not come from an error of judgment but from a number written down without its unit, picked up two days later by someone else.

And for the calculation itself, open AMEDEE Lab. Enter your trial, your volume and your target, and the tools return the quantity in every format, in the right unit. They suggest, you decide, and tasting keeps the last word.

Read next: Oak conversion table: chips, staves, tannins · What dose replaces a new barrel · How to dilute powder tannins