One of the amazing features that Hashem built into our ecosystem is the “oxygen cycle”, where animals and humans breathe in oxygen and exhale carbon dioxide, and plants and algae do exactly the opposite.  About 100 years ago, someone realized that not only did carbon dioxide play an important role in the survival of plant life, but it could also add some “sparkle” to otherwise bland beverages, and so began the seltzer and soda industry.  There is little in life that does not have a halachic implication, and this paper will discuss whether carbon dioxide can possibly be forbidden on Pesach.  The cRc thanks Dan Gruber, Technical Manager, CO2 System at Haffmans North America for providing considerable technical help in the preparation of this article.

There are three sources of carbon dioxide:

• A by-product of the fermentation of sugar into alcohol,¹ which is what happens whenever one produces wine, beer, whisky, bread or ethanol.  The carbon dioxide produced during this reaction is what provides the sparkle in champagne and beer.  Further discussion on this follows below.
• A by-product of the combustion of organic materials.²  The carbon dioxide that escapes in flue gases is most famously blamed as the culprit for global warming, as it is suggested that this gas creates a “greenhouse effect” when it collects in the atmosphere and prevents heat from escaping Earth.  [We will leave that discussion for the scientists and politicians].
• Minor sources including mines, petrochemicals, synthetic sources, and synthesis in a laboratory.

Carbon dioxide is a gas at room temperature, and typically, the gas recovered from fermentation (or combustion) is converted into a liquid or solid state for future use.  If carbon dioxide is recovered from a chametz fermentation of bread, beer, or whisky, is it forbidden on Pesach?  The earliest teshuvos on this topic are dated from when this industry was in its infancy, and all of the teshuvos assumed the carbon dioxide was in fact forbidden to the point that they did not even feel a need to explain the rationale for their ruling.³  In contrast, it is reported⁴ that when the question was posed to Rav Shlomo Zalman Auerbach, zt”l, approximately 30 years ago, he stated that the carbon dioxide is clearly permitted on Pesach.  Why did the Poskim take positions that are so diametrically opposed to one another?  We will see that a careful analysis of the relevant halachos shows that אלו ואלו דברי אלקים חיים , in fact both positions are correct!

Our discussion begins with the status of alcohol distilled from a non-kosher beverage.

Alcohol boils at about 173° F and water boils at 212° F.  Therefore if one heats an alcoholic beverage to somewhere between 173° and 212°, the alcohol will boil out but the water will not.  If the alcohol-laden vapors are captured and cooled, they will condense into a liquid which has a much higher concentration of alcohol than the original liquid did.  The aforementioned process is known as distillation, which is the method used to create whisky. 

What is the halacha if whisky is distilled from stam yayin?  Is it forbidden since the whisky/brandy clearly came from stam yayin or does it lose its association with the stam yayin while it is in the invisible gaseous state?  This is very similar to our original question, where the carbon dioxide begins in a liquid form (e.g. as beer), and then becomes a gas before being converted back into liquid or solid carbon dioxide.  

In the seminal teshuvah on the topic of whisky Rivash⁵ establishes that liquid condensed from the heating/boiling of stam yayin is forbidden, because the condensation is halachically considered a product of the original liquid.  One of Rivash’s proofs is from the Mishnayos in Machshirim 2:1-2, which differentiate between condensation which forms as a result of heating (e.g. a bathhouse) versus that which is a result of a cool environment (e.g. a cave), with the former having the status of the liquid it comes from while the latter does not.  A simple reading of this proof implies that the ruling is limited to distillation where the vapors escape as a result of heating the beverage, but would not apply to carbon dioxide which escape when the beer or whisky is at ambient temperature. 

However upon further consideration, Rivash seems to understand that the significance of a hot process is not the heat per se, but rather that in a hot process the steady and considerable amount of vapor/condensation formed provides a clear halachic link between the original stam yayin and the end product (i.e. the whisky).  Accordingly, since carbon dioxide recovered from a cold process also produces a steady and considerable stream of liquid (or solid) carbon dioxide, the liquid carbon dioxide should retain the status of the original chametz beverage.

This position – that vapors/condensate from a cold process can also retain the status of the original liquid – is borne out in another halacha, which is based on Gemara, Avodah Zara 66b-67a and cited in Shulchan Aruch Y.D. 108:4-5.  The halacha discusses dough or bread which is on a barrel of yayin nesech, and gives detailed directions as to when the bread does or does not absorb taste from vapors of the wine stored in the barrel.  Although the wine is at ambient temperature and has no direct contact with the bread, there are cases where the bread is forbidden, based on the invisible gaseous carryover of taste from the wine into the bread.  This demonstrates that if the taste of the forbidden food/liquid is perceptible in the final product, that final product is forbidden even if the transfer happened through the medium of a temporary gaseous state. 

With this understanding, we can now address the question of whether carbon dioxide recovered from a chametz fermentation should be forbidden on Pesach.  It turns out that the technology of recovering carbon dioxide has steadily progressed over the past 100 years.  At first scientists figured out how to liquefy the carbon dioxide escaping from these reactions but had no effective method of purifying these vapors.  As such, in those days, the liquid carbon dioxide likely did have a carryover of taste from the beer or whisky it was made from, and for that reason, the Poskim of that era concluded that the carbon dioxide was forbidden on Pesach.

However, in the past 50 years, the industry has developed 5 different methods of purifying the carbon dioxide⁶ – four while it is in the gaseous state, and a fifth after it is liquefied – to the point that nowadays carbon dioxide recovered from beer or whisky bears absolutely no taste of the original liquid it was created from.  We can surmise that that this change of facts is why when the question was presented to Rav Auerbach, he ruled that it is surely permitted!  Rav Auerbach appears to have held that a vapor/condensate only retains the status of the original liquid if it also retains the taste of that liquid, and since nowadays the carbon dioxide has absolutely no taste of the original beverage, it is not forbidden as chametz.  [See the footnote for an alternate explanation of these halachos.]⁷

Of the kashrus agencies we conferred with, we found that many chose to take a strict approach and not allow carbon dioxide from chametz or even kitnios (but they took varying approaches to verifying the source of the carbon dioxide)⁸ but others came to the conclusion outlined above that one may be lenient nowadays.⁹  Due to the (commendable) strictness with which people traditionally treat questions of chametz, the cRc only certifies seltzer or soda after verifying that the carbon dioxide is not recovered from chametz (but does accept it from kitnios sources).  While this may not be required on strict halachic grounds, it is within the spirit of חומרא דפסח to be machmir on this matter.

Postscript

The following are some relevant facts about the current carbon dioxide market:

• Nowadays, beer companies typically do collect the carbon dioxide vapors escaping from their fermenters for reuse in their products, and it is very rare for them to sell the carbon dioxide to others. 
• Most whisky and ethanol produced in the United States is kitnios, not chametz.
• Due to an overabundance of carbon dioxide byproduct, it is uncommon for a producer (e.g. a whisky or ethanol plant) to recover the carbon dioxide unless they have a specific buyer in mind.  In fact, typically the carbon dioxide resellers are the ones who install the collection equipment in the producer of their choice, and then remain with that producer for many years.  As such, although many new ethanol plants have opened up in the USA in recent years, it may take many years before the carbon dioxide produced in those plants is ever used in seltzer.