Newsletter

Technical Bulletin - Calculating Headspace


Ullage Calculations

Leaking wine bottles are often erroneously blamed on poorly performing closures, but unless the closure has serious physical defects, the reason for leakage is usually due to improper bottling practices and excess bottle pressure after bottling.

Wine bottle drawings from glass manufacturers show the suggested fill point for wine at 68ºF. The fill point is measured as the distance from the top of the bottle to the correct wine level in the bottle. These figures do not absolve the winery from their requirement to have a legal fill. They do, however, provide a good idea as to where the correct fill point should be. Generally, the fill point on the 750 ml bottle at 68°F will be approximately 64mm from the top. It is always best, however, to consult the drawing as a +/-3mm variance is possible.

The throat diameter of a standard, American 750ml bottle will vary slightly in the ullage area. On average, however, it is fair to say that the ullage with a 49mm cork and a 64mm fill height will average 4.8 ml. in volume. For a 45mm cork the correct volume would be 6.5 ml.

If the winery bottles at legal fill heights and with adequate vacuum to assure that there will be no more than 2 pounds relative pressure in the bottle at 68°F, it is very unlikely that the customer will ever complain about leaking corks.
The classic reason wines develop excess pressure in the bottles is that the bottles were overfilled in the first place. When this is combined with pressures of warming and expanding wine, leaking can become inevitable.

Temperature Effects
Based upon figures from "Principles and Practice of Winemaking” by Boulton et al, the thermal expansion of wine between 20ºC [68ºF] and 40ºC (104ºF] is .08%. This doesn't sound like much. It does, however, convert to .166 ml in volume per degree Fahrenheit. Thus, if a winery bottles at 58°F with 4.5 ml in ullage, that ullage will be reduced to under 3 ml at 68ºF and internal bottle pressure will have risen significantly.
There are three ways to achieve proper ullage levels and bottle pressure.
  • Bottle wine at 68ºF and fill to the level designated by the bottle manufacturer and confirmed by the winery.
  • Adjust the fill level to compensate for temperature differences. A good rule of thumb is to adjust the fill level by 0.55mm for every degree Fahrenheit above or below 68ºF.
  • Adjust vacuum levels to compensate for temperature differences. This method seems less reliable than adjusting fill levels because it places so much responsibility on the performance of bottling equipment. Internal bottle pressure needs to be equivalent to less than 2psi (relative) at 68ºF.

Fill Chart by Temperature*

Wine
Temperature
Fill Level
from Top
Ullage*
45mm Cork
49mm Cork
72ºF
61.3mm
15.3mm
11.3mm
71ºF
61.8mm
15.8mm
11.8mm
70ºF
62.4mm
16.4mm
12.4mm
69ºF
62.9mm
16.9mm
12.9mm
68ºF
63.5mm
17.5mm
13.5mm
67ºF
64.1mm
18.1mm
14.1mm
66ºF
64.6mm
18.6mm
14.6mm
65ºF
65.2mm
19.2mm
15.2mm
64ºF
65.7mm
19.7mm
15.7mm
63ºF
66.3mm
20.3mm
16.3mm
62ºF
66.8mm
20.8mm
16.8mm
61ºF
67.4mm
21.4mm
17.4mm
60ºF
67.9mm
21.9mm
17.9mm
59ºF
68.5mm
22.5mm
18.5mm
58ºF
69.0mm
23.0mm
19.0mm
57ºF
69.6mm
23.6mm
19.6mm
*Assumes cork recessed 1mm below bottle top

Bottle Pressure by Temperature*

Wine
Temperature
Fill Level
from Top
Max Pressure*
45mm Cork
49mm Cork
72ºF
63.5mm
4.6 psi
5.4 psi
71ºF
63.5mm
3.9 psi
4.5 psi
70ºF
63.5mm
3.2 psi
3.6 psi
69ºF
63.5mm
2.6 psi
2.8 psi
68ºF
63.5mm
2.0 psi
2.0 psi
67ºF
63.5mm
1.5 psi
1.3 psi
66ºF
63.5mm
1.0 psi
0.7 psi
65ºF
63.5mm
0.5 psi
0 psi
64ºF
63.5mm
0 psi
-0.5 psi
63ºF
63.5mm
-0.4 psi
-1.0 psi
62ºF
63.5mm
-0.8 psi
-1.5 psi
61ºF
63.5mm
-1.2 psi
-1.9 psi
60ºF
63.5mm
-1.6 psi
-2.3 psi
59ºF
63.5mm
-1.9 psi
-2.7 psi
58ºF
63.5mm
-2.2 psi
-3.1 psi
57ºF
63.5mm
-2.6 psi
-3.4 psi
*Assumes relative pressure - base of 16.2 psi

Calculations are based on specific dimensions for Bottle Type:
750ml Claret Premier (Cal Glass / Owens Brockway) - other bottles may differ.

Management Suggestions

One way of dealing with ullage calculations is for bottling managers to chart out target fill heights and internal bottle pressures by bottle type in advance of bottling. Though this will not eliminate their responsibility for a "legal fill'', it will provide an excellent guideline for good bottling.

It is also critical that wineries keep good ongoing records during the bottling day. At a minimum, the following protocols should be observed.

  • Freshly corked wines from each corker head should be checked at a minimum every hour for internal pressure [suggested interval is every 30 min].
  • Quality control should not rely on the temperature gauge at the filler. A thermometer should be dropped into one bottle ex-filler every half hour.
  • If bottling line Q.C. tests bottles that are out of spec for fill or vacuum at a specific temperature, the associated product should be quarantined, [preferably] flipped upright and checked out. Only when the problem is resolved, should cases be returned to regular inventory.
  • Q.C. should always check out the readings on cork probe gauges against one another in the morning and again at noon.
  • These gauges should also be used to check the functioning of the corker gauge [not vise versa].
  • If there is a problem with the vacuum on one or more of the corker heads, the line should be stopped until it is cleared. This should not be done "on the fly".

Maintaining Legal Volume

Legal fill levels are an important requirement. We recommend the following process:

  • Consult the bottle drawing.
  • Calculate the approximate fill height based upon the actual temperature of the wine.
  • Weigh one case of bottles empty. Record the empty weight of each together with its mold number. Run them through the filler. Weigh each individual bottle. Calculate the net difference [full versus empty]. In order to convert this figure to mLs at 68"F, divide the net by .9982g/mL [the specific gravity of water at 68"F].
  • If testing with wine you should re-calculate the specific gravity based on the wine used. Wine typically has a lower specific gravity than water.
  • Adjust fill heights as required.
  • If legal requirements force the ullage to be smaller than indicated by the internal pressure table, increasing the bottling vacuum can be used to compensate.
Specific Gravity of Water
g/mL
4
39
1.0000
20
68
0.9982
40
104
0.9922

Large Format Bottles

The ullage tables in this bulletin are designed for 750ml bottles, and calculations need to be adjusted for different bottle sizes. In particular, large format bottles can exhibit tremendous expansion under high temperatures.

For bottling conducted at 68ºF, the CQC suggests allowing 8ml of ullage for every Liter of wine. For a 3L bottle—that is 24ml. This target would be adjusted for different temperatures.

To determine the volume, place a mark (A) where the bottom of the cork is expected. Fill the bottle with water. Subtract 18ml and mark the fill height (B).