Headspace Calculators
Bottling operations require management of multiple variables to ensure proper wine development. Calculating proper ullage levels are necessary to maintain proper levels of internal bottle pressure over a range of storage temperatures. The two key variables are bottling temperature and headspace management.
Thermal Expansion is a critical factor in calculating fill heights during bottling. The most common miscalculation occurs when wineries do not compensate for bottling at cooler temperatures than the eventual storage conditions. This can lead to underestimating the headspace. For instance, wine bottled at 50°F will see approximately 2ml of headspace disappear at normal storage temperature of 68°F. Failing to take this expansion into consideration can lead to serious increases in internal pressure if the wine is exposed, for even several hours, to higher than normal storage temperatures.
Headspace management is important to avoid potential oxygen ingress. Most bottling lines use some combination of gas sparging and/or vacuum application. Lower internal pressure levels are preferred, and the NCC recommends a maximum of 2psi internal pressure after bottling at 68°F.
Here are two headspace calculators that offer a quick way to see the relationship of temperature, internal pressure, and ullage. One is designed for determining the minimum headspace volume at bottling. The second is designed for wines that have already been bottled, and illustrates the pressure and ullage levels that can be expected at different storage temperatures.
Headspace Calculator for Bottling Operations
Most bottle manufacturers will provide a drawing showing suggested fill heights. In addition to this information, it is important to consider wine temperature at bottling.
The Calculator for Bottling Operation provides recommendations for ullage volume, internal bottle pressure, and fill height based on bottling temperature and cork length.
The calculator assumes a standard bottle shape, and wineries are encouraged to confirm fill heights by measuring the volume between the bottom of the cork and the expected fill height level. An easy way to do so is: (1) mark the bottle where the bottom of the cork will appear, (2) fill the bottle to that mark with water, (3) using a graduated pipette, remove the volume of water corresponding to the ullage calculator, (4) mark the bottle at the top of the remaining liquid. That is the recommended fill height.
Headspace Calculator for Storage Conditions
Several years ago, a well-known wine writer expressed his frustration with corks "soaking up" wine when placed in the refrigerator overnight. With this calculator, he could have seen that a bottle transitioning from room temperature to a normal refrigerator will see the 750ml liquid compress by about 3ml. In the average wine bottle neck the fill height will be about 8mm lower after refrigeration.
The Calculator for Storage Condition calculates changes in headspace and internal bottle pressure at different temperature levels.
Enter current measurements for bottled wine stabilized at 68°F and calculate changes at the range of temperatures expected during storage.