Many books and articles that you read on fermenting wine talk about how you need to add nutrients and specifically nitrogen to ensure a healthy ferment. While lack of other nutrients can slow or stop fermentation prematurely, nitrogen is considered the number one cause for wine fermentation to slow or stop. This is because nitrogen is a key compound used in the transport of sugar into the yeast cell for processing. That means that the amount of nitrogen you need is really dependent on the amount of sugar present in your juice. Grape juice or must will normally contain more than twice the amount of sugar as apple or pear juice. Yet, many cider recipes include the addition of nutrients, specifically, nitrogen. Just like sugar varies depending on the fruit and how it is grown, nutrients naturally found in the fruit also vary. So the question of whether nutrients are needed doesn’t really have a straightforward answer. As I am often saying, the answer is that it depends. To help answer the questions of whether nutrients, and especially nitrogen is needed to make great hard cider, let’s explore a few key questions and the concepts behind their answers.
- What are the types of nitrogen and there sources?
- What is nitrogen’s role in the fermentation process?
- How much nitrogen is needed?
What are the types of nitrogen?
There are many sources of nitrogen including ammonium, amino acids, polypeptides, proteins, nitrates, amines, and nucleotides. But, these fall into two basic categories: organic and inorganic nitrogen. Chemically, organic nitrogen contains both carbon and hydrogen molecules as essential elements found in living organism. Inorganic nitrogen may have either carbon or hydrogen compounds but, they are not essential and the nitrogen is normally bound to other types of molecules. Living organism contain organic nitrogen and the type of organic nitrogen commonly found in apple juice and cider is from amino acids, proteins, and peptides. Inorganic nitrogen is more common from ammonium. This can often come from the orchard practices, like fertilizers. However, even within these groups, not all nitrogen sources are equal. In wine, the amino acid proline is often found in abundance(1). However, most yeast will not process or assimilate it. This highlights the next key concept of nitrogen, Yeast Assimilable Nitrogen or YAN. As indicated by the name, this is nitrogen that can be utilize or assimilated by yeast. This includes both organic nitrogen like free amino acids and some peptides as well as inorganic nitrogen like ammonium. From the perspective of how yeast function, both organic and inorganic nitrogen will transport sugar into the yeast cell. Therefore, you might think that adding either will ensure a good fermentation and result in a better cider. But, there is more to nitrogen than just enabling the transportation of sugar.
What is the role of nitrogen during fermentation?
Protein synthesis is the actual pathway that moves sugar through the yeast cell wall. It is sugar that the yeast wants to create the energy (ATP) it needs to function and reproduce. However, the proteins used in this process must be replaced. Otherwise, residual sugar can be present in the cider but the yeast cannot absorb it because it lacks the needed transport proteins. The ferment becomes stuck and highlights the importance of nitrogen. Nitrogen is needed to create the transport proteins and yeast do this by synthesizing amino acids. You may remember that proteins are made up of amino acids. There are numerous pathways that yeast can utilize to create the compounds, including proteins, needed to function and reproduce. The fermentation process home cider makers want is really the result of many pathways within the yeast cell. Often, yeast have multiple ways of creating or unlocking the same compound. This allows yeast to adapt to different environments. It is also the cause of sulfur aromas when nitrogen is lacking or in excess. Ultimately, nitrogen is a critical compound that can shutdown the yeast function even when sugar is readily available.
While nitrogen is critical for sugar transport into the yeast cell, the quality of the nitrogen is also critical to making great cider. This is where organic and inorganic sources of nitrogen begin to matter. Most yeast nutrients on the market are inorganic ammonium that are often found in the salt form Diammonium Phosphate or DAP. They dissolve easily in liquid and provide excellent amounts of YAN. In general, you should stop using DAP and other inorganic nutrients. Part of the reason is related to the last question regarding how much nitrogen cider needs. The main reason you should avoid inorganic nitrogen is because it doesn’t contribute and can even detract from the aroma profile of your hard cider. Nutrients supplying organic nitrogen, like Fermaid O from Lallemand, are Yeast Derivative Products or YDPs that generally consist of amino acids. Amino acids not only contain nitrogen but also contain precursor compounds for the formation of esters. That means when you use organic nutrients, you are not only providing nitrogen but you are providing other compounds used to create the aromatic profile of your cider. A. Ortiz-Julien and associates demonstrated how organic nitrogen enhanced the aromatic profile of wine while DAP actually decreased it(1). This leads us to the last key question, which is how much nitrogen do you really need to ferment cider.
How much nitrogen is needed?
When discussing wine fermentation, YAN levels below 150mg/liter are considered deficient(2). B. Dukes and associates published a table showing the YAN needed in wine to ensure complete fermentation for different sugar levels as defined by Brix(3). This is part of the problem because many have applied the 150 rule to cider but, hard cider isn’t wine. It generally has less than half of the available sugar. So, I extrapolated the table downward to the levels closer to that of most apple juice. As you can see, the YAN requirements are well below the 150mg/l indicated as the minimum recommended YAN amount. While fertilization of the orchard can impact the level of YAN, A. Alberti and his colleagues found that apple juice ranges from 27 to 574 mg/l of nitrogen. They also noted that 86.3% of the 51 apple varieties assessed had over 100mg/l. Based on my extrapolated chart and own experiments with unfertilized orchards, most apples you find will have sufficient nitrogen to fully ferment. Can you find an apple with high sugar and low nitrogen? Probably, but you will need to look hard to find it and, when you do, guard it. Why? Because these are the apples that will make naturally sweet hard cider. They will create what the keeving process does or what people are always seeking, which is a cider with natural residual sweetness at the end of fermentation. Note that I am just talking about the ability to ferment and not the aromatic profile of the cider. Adding inorganic nitrogen won’t help and may degrade the aroma profile of cider but adding organic nitrogen should improve it.
|Brix||Specific Gravity||YAN (mg/l)|
In summary, do you need to add nitrogen to apple juice to ensure a complete fermentation? Unlike wine, the answer is generally no. Also, if you want residual sweetness, adding nitrogen will ensure that doesn’t happen. The benefit that nitrogen can provide occurs when it is organic nitrogen, generally in the form of amino acids. This is generally done through a YDP product. Organic nitrogen can improve the quality of your cider by enhancing its aroma. For cider, avoid inorganic nitrogen like DAP. It most likely isn’t needed for fermentation and may reduce the aromatic properties.
(1) A. Ortiz-Julien and associates, Uncovering the relationship between nitrogen and aroma development, Wines & Vines, 116-121, January 2016
(2) G. Specht, Yeast fermentation management for improved wine quality, Woodhead Publishing Limited, 2010
(3) B. Dukes, Yeast Fermentation in Wine, Woodhead Publishing Limited, 2010
(4) A. Alberti and associates, Apple Wine Processing with Different Nitrogen Contents, Braz. Arch. Biol. Technol. v.54 n.3: pp. 551-558, May/June 2011
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