HTC of Wet Residues of the Brewing Process: Comprehensive Characterization of Produced Beer, Spent Grain and Valorized Residues

Abstract

Steady consumption of beer results in a steady output of residues, i.e., brewer's spent grain (BSG). Its valorization, using hydrothermal carbonization (HTC) seems sensible. However, a significant knowledge gap regarding the variability of this residue and its influence on the valorization process and its potential use in biorefineries exists. This study attempted to fill this gap by characterization of BSG in conjunction with the main product (beer), taking into accounts details of the brewing process. Moreover, different methods to assess the performance of HTC were investigated. Overall, the differences in terms of the fuel properties of both types of spent grain were much less stark, in comparison to the differences between the respective beers. The use of HTC as a pretreatment of BSG for subsequent use as a biorefinery feedstock can be considered beneficial. HTC was helpful in uniformization and improvement of the fuel properties. A significant decrease in the oxygen content and O/C ratio and improved grindability was achieved. The Weber method proved to be feasible for HTC productivity assessment for commercial installations, giving satisfactory results for most of the cases, contrary to traditional ash tracer method, which resulted in significant overestimations of the mass yield.However, for craft breweries located in big cities, disposal becomes more problematic [3]. There are also attempts to enrich food products with spent grains. Thus far, there have been trials with sausages [4] and bread [5]. However, consumers reported that such products represent a fiber aftertaste [6]. However, this is limited only to the relatively close vicinity of a brewery, due to relatively high moisture content, that could range between 70% up to 78% 70% [7][8][9]. Biological activity of these residues makes long term storage difficult. The literature reports ongoing work on various new ways of using BSG, including extraction of polyphenols [10,11], other anti-oxidants [12,13], functional cardioprotective lipids for pharmaceutic use [14], proteins [15], fodder for edible insects [16], material for disposable trays [17], natural rubber modifier [18], as well as feedstock for production of pigments [19] and biochar, for subsequent use as soil amendment [20] or sustainable material for electrodes [21].The potential use of this residue as a fuel has been suggested by several authors so far [7][8][9]22,23]. The relatively high initial moisture content of spent grain makes hydrothermal valorization techniques the most sensible choice [8,9]. Hydrothermal carbonization (HTC), also known as wet torrefaction, is a valorization process suitable for a range of low-quality solid biomass, especially with high initial moisture content [24,25]. Process temperature, reported in the literature, usually ranges between 180 • C and 260 • C [25][26][27][28][29][30]. As the process takes place in subcritical water, pressure has to be higher than saturation pressure of water for specific temperature [25][26][27][28][29][30]. In these conditions wa...

Brewer’s Spent Grains—Valuable Beer Industry By-Product

“…The study deemed low temperatures of the HTC process especially suitable, thanks to the high content of hemicellulose in the feedstock [ 88 ]. Jackowski et al observed that the yield of HTC can be determined by an indirect method [ 89 ]. The study also confirmed that HTC could increase the heating value of BSG and decrease the O/C ratio [ 89 ], indicating its suitability as a valorization method suitable for subsequent pyrolysis.…”

“…Jackowski et al observed that the yield of HTC can be determined by an indirect method [ 89 ]. The study also confirmed that HTC could increase the heating value of BSG and decrease the O/C ratio [ 89 ], indicating its suitability as a valorization method suitable for subsequent pyrolysis.…”

“…Moreover, HTC performed at 180 and 220 °C, and pyrolysis at 600 °C resulted in increased BET surface for pyrochars from a two-step process, when comparing to single-step pyrolysis at the same temperature [ 91 ]. Jackowski et al observed that the yield of HTC can be determined by an indirect method [ 89 ]. The study also confirmed that HTC could increase the heating value of BSG and decrease the O/C ratio [ 89 ].…”

Experimental and Computational Evaluation of Heavy Metal Cation Adsorption for Molecular Design of Hydrothermal Char

“…Hydrochar OFG abundance tends to decrease with increasing reaction conditions such as reaction time, temperature, and water-to-biomass ratio [46][47][48]. For many feeds [50][51][52][53][54], HTC can be performed over the temperature range from 160-180 • C and at reaction times <12 h to promote formation of OFGs. More aggressive conditions (≥200 • C) are preferred for other applications [55].…”

Synergetic Co-Production of Beer Colouring Agent and Solid Fuel from Brewers’ Spent Grain in the Circular Economy Perspective

“…Since the beer production process could significantly influence the properties of the corresponding BSG [82], the beer production process was performed in a controlled manner in a pilot-scale brewery and characterization of the main product of brewing (beer) is also an intrinsic part of this investigation. The residual BSG for further tests was produced in a pilot-scale brewing installation at the Wrocław University of Science and Technology.…”