Grams per hectoliter, units per hectoliter, milliliters: three units for one decision. This is the first source of dosing error we see, and it is expensive in both directions.
None of it is complicated, but none of it is automatic either. Here are the three conversions worth knowing, and the one that really does damage when it is forgotten.
Grams per hectoliter, not per liter
Our conversion table is expressed per hectoliter, like most oenological documents. Scientific literature, on the other hand, often works in grams per liter. The factor is simple: 100 g/hL is 1 g/L.
The working range of the table, 100 to 600 g/hL, is therefore 1 to 6 g/L, which places it inside the 2 to 10 g/L doses documented by the IFV for oak pieces. When you read a publication, always check the unit before comparing: a factor of one hundred gets noticed late.
Units per hectoliter, for staves
A stave is not weighed, it is counted. The table therefore gives units per hectoliter: 1.8 staves of 7 mm or 0.7 staves of 18 mm for the equivalent of a new barrel on a white.
Two things to watch. First, a 7 mm unit and an 18 mm unit do not weigh the same: the two columns do not convert into one another by a simple ratio, they are calibrated separately against the same oak level. Second, the decimals matter. On a 250 hL tank, 1.8 staves per hectoliter is 450 staves, and rounding to 2 makes it 500, which is eleven percent more wood.
The conversion that hurts: liquid tannins
This is the one to remember. Our liquid tannins are at 20 % concentration. One liter of liquid is therefore the equivalent of 200 g of powder.
The finishing tannin column of the table is expressed in powder. If your target is 4.7 g/hL and you dose 4.7 mL/hL of liquid, you are adding five times less than intended. The other way round, applying a value meant for liquid to a powder multiplies the dose by five, and that one cannot be undone: you do not take a tannin back out of a tank.
The rule fits on one line: divide the g/hL figure by 0.2 to get milliliters per hectoliter. 4.7 g/hL of powder is 23.5 mL/hL of liquid.
A worked example, on a 250 hL tank
Target: equivalent of a new barrel on a white, that is 350 g/hL of fine chips, or 4.7 g/hL of finishing tannin.
In chips: 350 x 250 = 87,500 g, so 87.5 kg for the tank. In powder tannin: 4.7 x 250 = 1,175 g. In liquid tannin at 20 %: 1,175 divided by 0.2 = 5,875 mL, so 5.9 liters. Three numbers, three products, one single oak level.
The habit that avoids all of it
Write the unit next to the figure, always, including on the sheet taped to the tank. Most of the overdoses reported to us do not come from a judgement error but from a number written down without its unit and picked up two days later by someone else.
And so you do not have to do the arithmetic in your head at ordering time, the dosage simulator does it for you: you enter your volume and your target, it returns the quantity in every format, in the right unit.
Read next: Oak conversion table: chips, staves, tannins · How to dilute powder tannins