Cracking the Corn: Corn Steep Liquor and Powder Fertilizers

By Wes Chun, Ph.D., Chief Science Officer

Introduction

Corn Steep Powder (CSP) is a fine, yellow to yellow-brown, water-soluble powder made by spray drying corn steep liquor (CSL).  Corn steep liquor is a concentrated liquid derived from the water that is used in the initial stage of the corn wet milling process.  Once considered a waste stream byproduct, its properties lent well for other uses.  The tan to brown liquid is denser than water and has an acid pH (3.7 - 4.7). Since it contains 40 to 60% water soluble corn solids, it has a variety of nutrients.  CSL has nitrogen in the form of amino acids and peptides, macro and micronutrients, and vitamins.  Because of this, it is particularly useful as an ingredient in microbiological growth media, or can be combined with gluten into an animal feed supplement.  Most recently it has been shown to be useful as a fertilizer, for the production of food, in the production of microbial products, and has some industrial applications.

Corn steep liquor and the more recently developed corn steep powder (CSP) are excellent replacements for other organic fertilizers such as fish emulsion, chicken litter, soybean meal, or feather meal.  Unlike most organic fertilizers, CSL and CSP nitrogen is readily available to the plant and not dependent on microbial activity for digestion and release. 

A Little About Corn

Corn or maize was first domesticated around 9,000 years ago in central Balsas river valley of southern Mexico.  Its ancestral parent is a native grass called teosinte.  Corn is likely the result of breeding teosinte for selective traits that made it into a high yielding, easily harvested crop.

The corn kernel is made up of the seed coat (pericarp), the endosperm, and the inner germ.  The pericarp is the fibrous outer covering of the kernel that can be used to produce hemicellulose and corn fiber oil.  The endosperm comprises nearly 82% of a kernel’s dry weight and can be used to produce gluten, corn meal cereals, edible and industrial corn starch, corn syrup, and corn sugar.  The germ is the living part of the corn kernel and contains vitamins, enzymes, minerals, and oils.  Products made from the germ include corn oil, glycerin, oil cake, and plastic resin.

Dry Milling of Corn

Recent archeological excavations in the Balsas region found an array of stone milling tools with maize residue on them.  The oldest tools were found in a layer of deposits that were 8,700 years old. Maize was then dispersed to Panama by 7,600 B.P. (Before Present = 1950), Colombia, Ecuador and Uruguay by 4,600 B.P., and eventually to Europe with the European explorers.

Dry milling is the physical or mechanical process of pounding or grinding grain to separate the endosperm from the pericarp and the germ, to make starch or ethanol (via fermentation).  Grinding mills use pin, hammer, or disk mills depending on the manufacturer.  The endosperm is recovered from dry milling in several sizes called grits (0.65 to 5.8 mm particles), meal (0.17 to 0.65 mm particles), and flour (<0.17 mm particles).  The products of dry milling are used in animal food, brewing, and breakfast cereals.  The recovered germ is processed for food use in cooking, mayonnaise, potato chips, soups, and sauces, and in livestock feed.

The Wet Milling Process

The wet milling process was first described by Orlando Jones in 1840 and patented in 1841 (U.S. Patent No. 2000).  His process uses an alkali material to separate the starch.  In 1842, Thomas Kingsford perfected the process he had learned from the wheat starch industry to make laundry starch from corn. The process has since undergone several modifications.  Most of the modern methods are based on a process described by Behr in 1909 (U.S. Patent No. 914,379) who also noted the nutritive value of the steep liquid.

The steeping process starts with soaking corn grain in open wooden tanks at 45 to 52 ^oC for 40 to 48 hours.  Sulfur dioxide (SO₂) is added to prevent microbial growth and to aid in solubilizing material.  Initial concentrations of SO₂are between 0.1 to 0.2% (pH 3.8 to 4.5) and decreases to 0.05% and 0.01% after 5 and 10 hours, respectively.  Active fermentation occurs in the steep water and lactic acid bacterial populations increase as SO₂concentrations decrease.  This separates the starch from the gluten, solubilizes and breaks down proteins, and softens the corn to facilitate grinding.  The amino acid and peptide rich steep liquor is collected and concentrated.  The concentrate is then used for a variety of secondary products.  It can be combined with gluten and fibrous materials for animal feed, used for microbiological purposes, used for municipal waste composting, used to stimulate crude oil biodegradation, used to stimulate wood decaying microbes, or used as a plant fertilizer.

Chemical Properties of Corn Steep Liquor

Corn steep liquor is a dense liquid (specific gravity of 1.25) with a pH of 3.7 to 4.1.  Most corn steep liquors have a nitrogen content around 4% mostly in the form of amino acids (alanine, arginine, aspartic acid, cystine, glutamic acid, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine tyrosine, and valine) and polypeptides.  Almost 25% of the amino acids in CSL is alanine.  Alanine plays a role in fruit quality (see Amino Acids and Their Function in Plants).  It also has around 3% of phosphorus and potassium.  CSLs also have a low sugar content (1 to 2%) and high lactic acid content (13 to 15%), a result of fermentation in the steep water by lactic acid bacteria.  The NPK content varies due to corn quality and processing differences between mills.  CSL contains considerable amounts of B-complex vitamins such as riboflavin, niacin, pantothenic acid, pyridoxine, and biotin with the exception of thiamine.  Vitamins play important roles when converted into cofactors for enzymes that are involved in stress reduction, nitrogen metabolism, nutrient transport, and photosynthesis.  CSL also has very low amounts of heavy metals such as Al, Ce, Cu, Fe, Pb, Mn, Mo, and Zn, low amounts of S, and moderate amounts of Mg (around 1%), and P (2-3%).

Uses for Corn Steep Liquor

Corn steep liquor has been used as a feed additive for livestock, and as a bait attractant for carp.  It is used in food production of yeasts, leavened dough products, and beer.  It is a good additive for microbial growth media and hence plays a vital part in the production of penicillin, E. colirecombinant proteins, and other bacterial products such as enzymes, organic acids, cellulose, and biodegradable plastics. It has industrial applications in converting municipal waste compost for organic farming, biodegradation of crude oil, microbial induced carbonate precipitation for remediation of cracks in concrete.  More recently, corn steep liquor has been used as a plant fertilizer.  As of April 29, 2011, corn steep liquor produced via the traditional corn wet milling process is considered to be non-synthetic and allowed for use in organic crop production.  Corn steep powder appeared circa 2000.

Amino Acids and Their Function in Plants

Agricultural Use of Corn Steep Liquor

Corn steep liquor was originally considered an industrial waste.  It wasn’t until the last 20 years when its use as an agricultural fertilizer was explored.  This could be due to its popularity (abundance and price) as a feed supplement, and its usefulness as a microbiological media ingredient for industrial recombinant products.  Technology improvements in viscous liquid handling and drying has changed all this. Today CSL can be used directly as a diluted liquid fertilizer, or as a dried pellet or powder fertilizer.

It can also be used indirectly by supporting growth of microorganisms that convert waste materials into useable fertilizer.  For example, CSL can be used to enhance the biological activity of composts, mulches, and city wastes. It is an effective media component for growing Aspergillusnigerto digest fish scales to produce an organic fertilizer.  

Surprisingly, despite the relatively rich nutritive value of CSL that obviously makes it an excellent fertilizer, there are only a handful of reports that use or test CSL or CSP as a fertilizer.  The earliest report occurred in 1992 when CSL use increased mung bean yields by 17%, and increased germination and productivity in wheat. In 2000, CSL was shown to be an excellent fertilizer on tomato as long as additional calcium was used for fruit production.  It was also noted that application of the liquid fertilizer to the soil surface promoted shallower root growth (artifact of the application method) but the CSL treated roots were thicker when compared to roots that were fed synthetic fertilizer. In 2003, it was reported that the nitrogen levels in CSL were too low (remember there was variability in N content depending of feedstock source and wet milling process) and resulted in lower yield and sugar production in muskmelon.  Supplementing with liquid cattle waste eliminated the problem.  Between 2006 and 2007, University of Illinois researchers used a total of 9 weekly applications of CSL on turf.  They reported that it worked as well as urea or ammonium sulfate and noted less potential for injury.  They conjectured that CSL increased soil biological activities and soil structure.

CSL may have additional benefits in addition to its high nutritive value.  In 2014, antimicrobial activity was shown against E. coli, Salmonellaenteritidis, Staphylococcusaureus, and Vibrioparahaemolyticus.  This helped alleviate any food safety concerns when using or storing CSL.  That same year, use of CSL showed suppression of Fusarium oxysporum f. sp. lactucaein hydroponic lettuce when compared to synthetic fertilizer treatment.  In 2015, CSL was used in a blend with fish emulsion to get a 2.5 - 1.1 - 1.2 and compared to a fish-molasses blend 4 - 0 - 1.7.  Applied via drip, between 56 kg and 90 kg N resulted in no difference between fertilizers mixes in growth, yield, fruit quality, on Marion and Black Diamond varieties of blackberry. 

People Crack Corn and why we Care

Corn steep liquor, once a major waste product of corn wet-milling, has now been repurposed for a variety of uses. Use as a fertilizer is a more recent development that has the potential to impact the organic plant growth market. Drying viscous liquids have always been problematic.  However, methods for drying CSL were patented in 1999 and 2012 giving rise to corn steep powder. Dried into a soluble powder, it is an easily transportable fertilizer that is as efficient as urea and ammonium sulfate.  It has major advantages over synthetic nitrogen since it is less likely to cause injury and the nitrogen is present in ready to use amino acid and peptide forms.  It has an advantage over other organic fertilizers like chicken litter that requires microbial activity to convert the nitrogen into plant useable form.  It is a fairly complete general fertilizer for plants. Like all other general fertilizers, additional supplementation with specific macro or micronutrients may be needed to meet specific needs of the crop.  The product can be formulated as a dry water-soluble powder or as a pellet. Thus, it is flexible for any dry or liquid application method.  Lastly, this is one of a few products that meets consumer demands for sustainability, food safety, and preference for organic produced foods. Corn steep powder should be used as part of an overall nutrient management program and applied based on the results of a soil and plant analysis of a given crop.