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Chicago, IL

Green coffee beans are often fermented before being rinsed, dried, and roasted. Fermentation allows naturally occurring bacteria and yeast to break down some of the sugars on the outside layer of the coffee bean, enhancing the flavor of the bean. Sometimes a foreign yeast is added to help the process along or bring out specific flavor profiles. A certain locally produced roast uses red wine yeast (fed on non-kosher red wine) to assist fermentation. Does this constitute a kashrut issue?


This is a great question. The case is one where grape juice (technically “must”) is allowed to ferment and the yeast extracted from that process is added to the fermenting coffee beans. The wine/fermenting grape juice is not put in the mixture, but rather the yeast that was colonizing on the fermenting grape juice is collected and then added to the mixture.

So – we have to look at a number of issues –

1. Is grape juice a problem of stam yeinam? Answer – yes, even 1 day old (assuming it has not been pasteurized) – see Shulchan Arukh YD 123:17.

2. How much of a problem is wine/grape juice nowadays, given that in some halakhot we say that Christians are not ovdei avodah zarah, and although stam yeinam applies with all non-Jews, the Halakha might be different if it isn’t touched directly, and only been poured (which is often the case). For that, see my teshuva. For our purposes, we will take that standard approach that it is a problem.

3. If we are only talking about the yeast that is taken from the wine culture, then I cannot see what the problem is. The yeast colonizes on the wine from the air, or from what was present in the grape itself, but it is not produced by the wine. Kashrut industries generally assume that the yeast would have the status of the culture, but this makes no sense to me. A cow that drinks wine isn’t assur, and neither should yeast that feeds off of wine. So based on this, everything is fine, which is my basic pesak.

4. Assuming we followed the standard kashrut industry approach, that would treat wine-grown yeast as some by-product of wine, or assuming that some of the wine itself is added to the fermenting coffee beans, then we have an issue of wine causing fermenting – מחמיץ – which is a halakhic problem, even regardless of taste (similar to the concern of ma’amid – since it has a profound impact on the food). See Mishnah Orlah 2:1-17, and many sugyot in Shas.

5. In this case, the coffee is already fermenting and able to ferment by itself. So, that would make this a case of זה זוה גורם – both the coffee-based yeast and the wine-based yeast are contributing to the fermenting. However, that is not really accurate here. The general halakhic pesak is that זה וזה גורם is not a problem when neither ingredient can do the job alone (see Mishnah Orlah 2:11). If each can do the job of causing fermentation alone, then the presence of the issur is enough to make it assur (Mishnah Orlah 2:9; Rambam in Ma’achalot Assurot 16:16; Shulchan Arukh YD 87:11, Rema and Shakh 36. Although Tosafot on Pesachim 27a, s.v. ad, is lenient in that case).

6. From everything you wrote, it is clear that the coffee can do the fermenting alone. I have a hard time believing that if there was no yeast present in the coffee/water mixture, that the amount of wine-based yeast would suffice to have the coffee ferment as much as it needed to.

7. Thus, the wine-based yeast is adding to the fermenting, but not doing the job of fermenting – it is מסייע not זה וזה גורם (or said another way, it is a case of זה יכול וזה אינו יכול). That is not a concern of machmitz. Rav Moshe says essentially the same thing in the case of cottage cheese to which they may have added rennet to cause it to congeal (מעמיד). See Iggrot Moshe YD 2:48. In his case he says that “maybe” it is mutar based on זה וזה גורם even according to those who normally say זה וזה גורם is assur. It is not clear to me to whom he is referring that זה וזה גורם is assur, unless he means positions in the Gemara, not in terms of pesak and lema’aseh (and he at times deals with such Gemara positions on זה וזה in his other teshuvot). Regardless, his doubt in the case of cottage cheese seems to be because the rennet is speeding up the process, so it is actually doing an active role, more than what would have happened without it. That is not the case here. The speed is the same, the flavor profile is what is different. Regarding that, Rav Moshe says:

ואף שאומרים שגם בגבינה זו דקאטעד טשיז נותנים מעט רענעט, הנה אף אם נימא שרענעט הוא דבר אסור מסתבר שאין להחשיבו מעמיד, כיון דאין להגבינה שום תועלת מזה דלא משובח טעם הגבינה במעט הרענעט שנתנו שם יותר מכפי שהועמדו מעצמם מצד הזמן והחום, ומה שמיהר להעמיד ע”י הרענעט אין זה כלום בטובת הגבינה אלא הוא טובת המוכר שיש לו הגבינות איזה ימים קודם ואין שייך לאסור מצד זה מטעם שהרענעט מעמיד. וגם לבד סברא זו הרי הוא רק זה וזה גורם, ועוד עדיף דהזמן והחום היו מעמידין גם בעצמן והרענעט המעט לא היה מעמיד בעצמו כלל רק בצירוף הזמן והחום הועיל להקדים ההעמדה ויש להחשיב זה רק כמסייע בעלמא שאולי אף הסוברים דזו”ז גורם אסור היו מתירים בכאן.

8. So we are left with the issue of ta’am. Does the yeast add grape flavor? While you did say that it impacts the flavor profile of the coffee, it seems clear that this means that the fermenting allows different tastes of the coffee to come out, not that the coffee absorbs grape flavor. This is of course true, since it is the yeast that is interacting with the coffee, not the grape juice. Thus, any impact in flavor is not the taste of the wine, and totally permitted. This is somewhat similar to discussions of adding an ingredient to impact the flavor, but the resultant flavor is not that of the forbidden ingredient, but one created by the interaction of the flavors. (There is some discussion of this regarding sherry casks, see here, p. 33-34, for example.) However, this case is much better, as there is no mixing of grape flavor with coffee flavor, it is just that the yeast allows the coffee’s own flavor to come out. Thus, it is fully permissible.

In conclusion: It is permissible because: (a) the yeast grows on the grape juice/wine but is not a product of it, (b) even if the wine itself were added (or one were to be strict with (a)), it would be permitted because the wine only assists, in a non-necessary way, the act of fermentation, so it does not have a status of machmitz, and (c) although done for the sake of the final flavor, this is the flavor of the bean itself that is being brought out, and not in any way the flavor of wine that is being absorbed by the bean.


(From a different rabbi:) – במחילת כבוד תורת רבינו הרמה, in terms of metziyut I think when there are live yeast in wine the yeast (colonies of fugal cells) are a solid that absorbs the liquid wine. It is impossible to separate the yeast culture from the culture medium. Only after growing the yeast in several changes of medium would the wine actually be removed.

I researched something similar regarding bacterial cultures for yogurt (BeMareh HaBazak has a teshuva about this) and there’s a Tosefta in Pesachim which may be relevant about how many batches of dough until the sourdough is no longer chametz she’avar alav haPesach.


Thank you for the clarification. Two points:

  1. Regardless, my pesak still holds, for the reasons I wrote – even if the wine itself is used, it is a trivial amount, not notein ta’am, and not machmitz.
  2. From what I’ve been able to research, the goal is the yeast itself. The growth medium is not the point. So if I have wine-grown yeast, which I have separated as much as reasonably possible from the wine culture, and I am now putting that yeast into fermenting coffee beans, then the possible status of “machmitz” here would the yeast, not the small amount of wine present. In other words, even if some wine goes in, it is incidental and definitely not considered the potential machmitz and hence definitely batel. (As indicated above, it is regardless not a machmitz in this case because it is not able to do the fermenting on its own. The point here is that even if it were present in greater amounts and able to effect the fermenting, it would not be considered as a machmitz since the focus is on the extracted yeast and not the wine itself).

I think there is a key conceptual question here – if I put in the wine itself to cause fermentation, then even though the fermentation is being caused by the yeast in the wine, halakhically, it is defined as the wine as the fermenting agent (מחמיץ). If, on the other hand, I was able to totally extract the yeast from the wine, then the yeast would be the fermenting agent (it would not be considered a wine derivative). In a middle case, where you are focused on the yeast, and trying to extract it from the wine, but the two cannot be totally separated from one another – then I would consider it that you are adding yeast as a machmitz, with some incidental wine present. I do understand (although am not inclined to agree with) those who say that this is still like the former case and the wine is the machmitz.