barrels and topping up

: Wow! That sounds like a _lot_ of evaporative loss to me. I probably lose : about the same volume over the same length of time from a barrel almost 4 : times the size. : : I'd guess that your losses are that high because the staves are thinner in : your barrel than they are in my 228 liter export barrels, which are an inch : thick. Either that, or you recently filled a new barrel and it's still : soaking up wine. : : Tom S

My experience has been similar to Glens. I have two American Oak barrels, 1 Hungarian and this year added a French barrel (Moreau). The grain on the French is by far the tightest looking of the barrels and although it is the newest (the others are at least 4 years old) my impression is that it shows the least amount of evaporative loss. I will have to start taking careful notes of the added volumes to see if this is the case. Tim

I suspect that actually opening the barrel for topping contributes much less significantly than the diffusion of oxygen through the staves. After all, how long is the surface of the wine exposed during topping, and how big is that surface? OTOH, the surface of the wine within the aggregate of all the staves and heads is very much larger, and is exposed to air for the entire time the wine is in the barrel. Also, since the wine penetrates to varying depths within the staves the surface area exposed to diffusion through the staves will be textured, and therefore have a much greater effective surface area than the inside surface of the barrel.

That used to be more common when redwood bungs were still in use and before the advent of steel tubing barrel racks, but there are probably still wineries that do it that way with silicone bungs. I haven't seen rolled barrels in quite awhile, and AFAIC that's not a desirable approach. I need to keep closer tabs on the progress of my wines.

Incidentally, I remember that the Parducci winery used to bung barrels tight and stand them on _end_ on stacked pallets! That would make me _very_ nervous.

Tom S

Please let me try my arithmetic again.

A new, 225 liter barrel exchanges, through the staves and heads, about 2 ml of oxygen (O2) per liter of wine per year .

Therefore, a 225 liter barrel exchanges 2 X 225 = 450 ml of O2 per year. So, 450 / 52 = 8.6 ml of oxygen per week goes into the barrel through the staves.

Air contains about 20% oxygen.

If a 225 liter barrel is topped up once each week, and if 10 ml of head space remains in the barrel when the bung is replaced after topping up, then

2 ml of oxygen is introduced into the barrel (any O2 in the barrel when the bung is replaced will end up in the wine). 10 ml of head space introduces about 20% ( 2 / 10.6) of the weekly oxygen input.

But, 10 ml of head space after topping is a small amount. If 100 ml of head space remains when the bung is replaced, then 20 ml of O2 is introduced into the barrel. In this case, weekly topping up introduces about 2.5 times more O2 than that coming in through the staves.

What am I missing here???

Only one little thing that I can think of. I don't know about you, but when I top and bung a barrel I leave _zero_ headspace - not 100 ml. Not even 10 ml. Zero.

I don't use cupped bungs because I don't want any air trapped when I bung a barrel. Frankly, I don't understand why Boswell even makes them.

Tom S

Ullage (topping-up) causes the oxygen exposure in oak barrels. Oxygen does not enter through the staves or head of a sound securely bunged barrel. Water and alcohol will permeate outward creating a vacuum in the barrel. Examination of the stave cross-section reveals the "wine side" to be "wine logged" or saturated to a average depth of

2- 6 mm. Progressing outward the moisture content abruptly diminishes to 18% at the centre of the stave and 8% to 12% at the outer surface relative to the cellar humidity. The point being, that were oxygen to gain access to the wine via the staves or head, the inner 6 mm would show evidence of oxidation. Such evidence in sound securely bunged barrels does not exist as Singleton, Vernon L., elaborates "Vinifera Wine Growers Journal", Vol. 8, No. 4,(1981:231). Whether the barrel is loose-bunged or tight-bunged and the cellar temperature and humidity influence the evaporative losses and volume of ullage. A barrel is said to be loose bunged when the bung is topmost and above the wine level. Tight bunged when the (silicone) bung is fitted and the barrel rotated such that the bung is beneath the wine surface, which in my opinion offers the best seal against oxygen infiltration via the vacuum effect and the bung position. Oxygen does not enter through the staves or head of a sound securely bunged barrel. Water and alcohol will permeate outward creating a vacuum which is apparent when you pull a secure bung. Wine in topped up barrels is exposed to oxygen during racking and topping made necessary by evaporative ullage (Angel's Share). Zinman

Zinman, Until a few month ago, I agreed with your assessment of oxygen transport through barrels, but I don't agree now. Please take a look at the info here

and at the material presented in reference #3 of the above paper. Apparently barrel dynamics were never measured until recently. lum

That's a prestigious reference (if a little out of date). IOW, I'm not convinced.

Temperature obviously increases evaporative losses. The effect of humidity is to shift the ratio of alcohol evaporation vs water evaporation. In a humid cellar, alcohol evaporates in a higher proportion than does water. The opposite occurs in a dry cellar.

A barrel is said to be loose bunged when the bung is

Au contraire. Tight bunged means exactly what it says: the bung is jammed hard into the bunghole such that it forms an airtight seal. It has nothing to do with rotation of the barrel or where the surface of the wine is with respect to the bung. A barrel with the bung vertical can definitely be hermetically sealed in this fashion.

Loose bunging is when the bung is merely set in place, allowing the barrel to vent pressure (typically). This is often done when ML is not yet complete. Some winemakers use one-way "venting" silicone bungs or airlocks for this purpose, but many do not. I've even seen baggies filled with bentonite laid across the bunghole to effect "loose bunging".

Wine in topped

True, but that effect is considered minor in comparison to the slow diffusion of oxygen through the staves. Only glass or metal are capable of totally barring the diffusion of most gases. Plastics are not, although some plastics are better than others. Porous, organic materials like wood are much more permeable than most plastics.

Tom S