FAN (free amino nitrogen)

Ingredients
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I recently had a fellow homebrewer graciously review my process and an interesting topic was mentioned that I have begun researching. I have not concerned myself with FAN thinking I don’t need to know how to build a watch to tell time. Brewing can be as easy as soak some grain, boil it with some hops, throw in some yeast and out pops beer. …but the more I dig the more I find it’s not that simple. This brewing stuff can get deep with the quickness. I thought I’d run it up the flag pole and see how others view FAN.

It is well understood that excess FAN correlates to beer staling and is negatively correlated to beer stability. Beer stability refers to the capacity of beer to maintain its original quality, flavor, and chemical profile as long as possible. (Jesse Bussard, Craft Malting)

Free amino nitrogen (FAN) is a term used to describe the amount of nitrogen-containing compounds found in wort that may be metabolized by yeast during the fermentation process. FAN includes amino acids usually found in wort along with ammonia and small peptides. (Hill & Stewart, 2019)

Some brewing scientists regard FAN as a better index for the prediction of healthy yeast growth, viability, vitality, fermentation efficiency, and hence beer quality and stability. (Graham G. Stewart, The Oxford Companion to Beer)

There are many mechanisms that result in the staling of beer, including oxidation mechanisms (e.g. lipids, free radicals, higher alcohols, and iso-alpha-acids) and aldol condensation resulting in the formation of a cardboard-like or papery off-flavor. However, the majority of beer staling results from amino acids transforming into chemical compounds called “Strecker aldehydes” (SA). (Yin, X. S. Malt.  American Society of Brewing Chemists, 2021). That’s where the excess FAN plays a role.

The majority of the FAN is consumed within the initial 24–36 h of fermentation, after which yeast growth generally stops. However, differences in FAN uptake between lager and ale yeast strains have been identified. The concentration of wort FAN required by yeast under normal brewing conditions is directly proportional to yeast growth and affects beer maturation. There is also a correlation between initial FAN levels and the amount of ethanol produced.  (Graham G. Stewart, The Oxford Companion to Beer)

The comment I received was based on not using O2 to aerate my wort. By pitching the correct amount of yeast into properly aerated wort, FAN can be consumed and create a more stable beer.  Sounds easy enough.

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We meadmakers are familiar with FAN because traditional mead must only has about 20 ppm and 200-300 ppm is optimal. Yeast nutrient contains nitrogen but because of the higher levels of FAN desired most also add disodium phosphate (DAP) in staggered nutrient additions. Mead must with a lot of fruit has much higher FAN levels.
I have long heard that wort contatins more than adequate FAN.
What is your thinking about this, BB? At first I thought this was going to be about adding nitrogen but it seems like you are looking into adding O2 to help consume more FAN, is that right?
If it is the case that excess FAN is in homebrewers wort then the practice of adding yeast nutrient “just in case” or “because it does no harm” should be questioned as it adds some nitrogen.

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Great points. I understand a stuck fermentation can occur in mead, wine, and even extract brewing because of a lack of FAN. This could be the reason so many extract brewers reach a 1.020 wall.

However, you are correct. As an all grain brewer, consuming excess FAN is the comment I received and am researching. Adding O2 prior to pitch is what I am looking into.  I have also begun looking into yeast nutrients. Seems they are not all created equal.

An interesting point I discovered is that low OG wort actually may benefit from nitrogen nutrients while higher OG wort has enough (or could be excess) FAN but could benefit from other nutrients.

Now, I am learning that different yeast require different levels of FAN so the one size fits all XXX ppm is a question.

In my case hitting the wort with O2 prior to pitch may be all that it takes.

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I will be following your postings about this and appreciate that you are sharing this info. There seems to be a potential new tool for our toolboxes here, and possibly a cheap and easy one at that.
Your point about OG is especially interesting. While my experimenting with low cal/carb beers has been largely successful my FGs have not been as low as I hoped, even with enzymes. So maybe the right nutrient would help.

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Interesting how things go around.  25 years ago, FAN was a big topic on Homebrew Digest.

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I remember reading about it in Brewing Techniques magazine

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Same era, huh? Interesting to see things rediscovered.

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Where is the speculation coming from that the beers have excess FAN?  Although it’s possible, the previous focus seemed to be on beers not having enough for a healthy fermentation (malt extract beers, adjunct beers, beers with simple sugar additions) to the point that people were adding rests in the Peptidase range (131).

Not saying it isn’t possible, but it seems like an invented problem without any specific evidence.

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Back in HBD days, the talk was that the trub provided FAN, which is why you don’t want to remove it all.  Also gives credence to the observation that beer fermented on trub is clearer and better tasting.

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Evidently, it’s found in brewing science publications:

“…excess FAN correlates to beer staling and is negatively correlated to beer stability…”

“…a complex cascade of chemical reactions occurs between amino acids and dicarbonyls that form SA when the beer is in its final package. The amino acids are a product of excess FAN at the end of fermentation, and the dicarbonyls are a product of Maillard reactions.”

Mallet, J. Malt: A practical guide from field to brewhouse.  (Brewers Publications, 2014)

Briggs, D. E., Brookes, P. A., Stevens, R. & Boulton, C. A. Brewing: Science and Practice.  (Elsevier Science & Technology, 2004)

Yin, X. S. Malt.  (American Society of Brewing Chemists, 2021)

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What makes you think you have excess FAN?

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Nothing really. It was a comment I began to investigate.

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Got it. I didn’t know if you had specifically experienced staling or other problems.  Unless there was an easy way to measure the FAN in your wort, I’m not sure how you’d figure out how much yeast growth is needed to consume it other than trying to pitch the “right” amount of yeast and going by worked in the past.

Would this be a general problem for dry yeast, where growth isn’t required (supposedly) due to high cell counts?

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Well, that’s what I’m trying to investigate.

I use the  mfr pitch rate calculator so I believe my pitch rate is high enough. …and the tech data sheet says aeration is not required for initial use.

But I’ve yet to find a source discussing dry yeast aeration with respect to FAN.

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You can obtain FAN from “malt analyses” that maltsters are providing.

Target for FAN in craft 2 row is in range 180-200. 6 row is higher.

Now I am going to say it again. Unless you ship your beer in hot container on the other side of world, you do not need to worry about it.

Just because something is applicable to commercial brewing it might not apply to your scale.

People who make difference in FAN are msltsters.

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Keep saying that so I’m not the only one!

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This a string is a little old, but it caught my interest. Excessive FAN is seen as a problem, but it’s not so much a problem with Continental malt. The FAN level is directly correlated to protein content.

  • Fan levels are reduced by yeast growth, the reduction of FAN from pitch to maximum yeast density is directly corelated. So overall growth of biomass will reduce the final FAN level. Higher levels of wort aeration can reduce the final FAN levels by promoting a higher biomass growth, more yeast growth = less FAN in beer.

  • Breweries that use European malt have more of a problem with not enough FAN due to lower levels of protein, where as North American has a greater amount of protein and excessive FAN is a problem. The use of adjuncts reduces FAN levels.

  • North America barley crop standards allow for more protein, up to 11-12%. This allows farmers to use more nitrogen fertilizer to increase crop yields, European yields per acre are lower and this drives the cost of barley up.

Is FAN a big problem for most brewers? Depends on the malt and yeast growth.

Here’s a really interesting podcast with Joe Hertrich about malt and how North American 2 row malt came to overtake 6 row.

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I appreciate your comments. Can you weigh in on this:

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The issue isn’t about dry or liquid yeast, but more to do with pitch rates. Most homebrewers are likely to under pitch than over pitch and it might be a little easier to over pitch with dry yeast due to the higher viable yeast counts.

The bottom line is to pitch the correct amount of yeast for the style and yeast strain you are using. I don’t believe FAN is as big of an issue as post fermentation oxygen ingress when it comes to staling, but I think it’s interesting. The protein content of the malt has a big impact on beer, from mash to glass. At levels above 11% total protein it becomes more difficult to work with. The maltster can only work with the raw material they get, high protein malts produce high FAN malts.

The podcast I linked to is very interesting, I learned a lot from it. Joe Hertrich is extremely knowledgeable on malt in general.

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Thx.

I use the mfr pitch rate calculator so I feel confident in my pitch rate.

When I received the comments on my process the same podcast was recommended. Admittedly, I have not listened to it yet. …but I’ll ck it out soon.